diff --git a/.env b/.env
index f13f7deb..f62418b8 100644
--- a/.env
+++ b/.env
@@ -1,7 +1,7 @@
 DATABASE_URL="file:./dev.sqlite3?connection_limit=1"
 
 NEXT_PUBLIC_BASE_URL="http://localhost:3000"
-NEXT_PUBLIC_COURSE_ID_TO_LECTURE_IDS_JSON={"tuBeginner1":["8d692b48-8c19-4679-8d8f-3f27a051d44d","d4de75e2-758b-4500-b38e-96213c360527","99045fdf-6cb5-4947-b934-8b1bc5831bbd","37632776-e3ab-4cc5-ae08-934caf2ada53","8fbc94d3-d20c-4457-8997-61e85b3516d9","35957643-c106-4a97-8073-6705c39ab9a6","045094ae-1f5c-4caf-bc33-a86af985f13b","84805179-12cf-4871-969e-fb39e6ad767a"],"tuBeginner2":["5ba06885-2044-4c1e-bd65-2a9c5e9c9e39"],"test":["6481cd2e-5143-4a99-9c86-dd93b7254211"]}
+NEXT_PUBLIC_COURSE_ID_TO_LECTURE_IDS_JSON={"tuBeginner1":["8d692b48-8c19-4679-8d8f-3f27a051d44d","d4de75e2-758b-4500-b38e-96213c360527","99045fdf-6cb5-4947-b934-8b1bc5831bbd","37632776-e3ab-4cc5-ae08-934caf2ada53","8fbc94d3-d20c-4457-8997-61e85b3516d9","35957643-c106-4a97-8073-6705c39ab9a6","045094ae-1f5c-4caf-bc33-a86af985f13b","84805179-12cf-4871-969e-fb39e6ad767a"],"tuBeginner2":["8d692b48-8c19-4679-8d8f-3f27a051d44d","d4de75e2-758b-4500-b38e-96213c360527","99045fdf-6cb5-4947-b934-8b1bc5831bbd","37632776-e3ab-4cc5-ae08-934caf2ada53","8fbc94d3-d20c-4457-8997-61e85b3516d9","35957643-c106-4a97-8073-6705c39ab9a6","045094ae-1f5c-4caf-bc33-a86af985f13b","84805179-12cf-4871-969e-fb39e6ad767a"],"test":["8d692b48-8c19-4679-8d8f-3f27a051d44d"]}
 
 SUPERTOKENS_URI="https://st-dev-9ecbdd10-5f8e-11ef-a204-f3d2d26d900f.aws.supertokens.io"
 SUPERTOKENS_API_KEY="J-1qlZUxj8wo1xO3DZBu9rUwZc"
diff --git a/README.md b/README.md
index 49f2cb6d..4e008dad 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ An educational web app for training program tracing skills.
    ```
 
 2. Open lectures via the following URLs:
+
    - 初級プログラミングⅠ
      1. http://localhost:3000/courses/tuBeginner1/lectures/8d692b48-8c19-4679-8d8f-3f27a051d44d
      2. http://localhost:3000/courses/tuBeginner1/lectures/d4de75e2-758b-4500-b38e-96213c360527
@@ -51,7 +52,9 @@ An educational web app for training program tracing skills.
      7. http://localhost:3000/courses/tuBeginner1/lectures/045094ae-1f5c-4caf-bc33-a86af985f13b
      8. http://localhost:3000/courses/tuBeginner1/lectures/84805179-12cf-4871-969e-fb39e6ad767a
    - 初級プログラミングⅡ
-     1. http://localhost:3000/courses/tuBeginner2/lectures/5ba06885-2044-4c1e-bd65-2a9c5e9c9e39
+     1. http://localhost:3000/courses/tuBeginner2/lectures/8d692b48-8c19-4679-8d8f-3f27a051d44d
+   - 動作確認用
+     1. http://localhost:3000/courses/test/lectures/8d692b48-8c19-4679-8d8f-3f27a051d44d
 
    The URL format is as follows.
    You can find parameter values from `NEXT_PUBLIC_COURSE_ID_TO_LECTURE_IDS_JSON` in the `.env` file.
diff --git a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/BoardEditor.tsx b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/BoardEditor.tsx
index 67f377ba..1fb741c8 100644
--- a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/BoardEditor.tsx
+++ b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/BoardEditor.tsx
@@ -75,7 +75,7 @@ export const BoardEditor = forwardRef<TurtleGraphicsHandle, TurtleGraphicsProps>
       updateVariables(props.initialVariables);
       if (!keepSelectedCell) setSelectedCell(undefined);
     },
-    [previousTraceItem, props.initialVariables, updateBoard, updateTurtles]
+    [previousTraceItem, props.initialVariables, updateBoard, updateTurtles, updateVariables]
   );
 
   useImperativeHandle(ref, () => ({
@@ -84,8 +84,7 @@ export const BoardEditor = forwardRef<TurtleGraphicsHandle, TurtleGraphicsProps>
 
   useEffect(() => {
     initialize(props.previousTraceItemIndex >= 1);
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [props.previousTraceItemIndex, props.problem]);
+  }, [props.previousTraceItemIndex, initialize]); // We should include initialize because it depends on props.initialVariables
 
   const updateTurtle = (currentTurtle: TurtleTrace, newTurtle: Partial<TurtleTrace>): void => {
     updateTurtles((draft) => {
@@ -116,7 +115,8 @@ export const BoardEditor = forwardRef<TurtleGraphicsHandle, TurtleGraphicsProps>
         zenkakuAlphanumericalsToHankaku(value) !==
         zenkakuAlphanumericalsToHankaku(props.currentVariables[name].toString())
       ) {
-        locations.push(`変数${name}`);
+        const isExpression = /[+\-*/%()[\]\\.]/.test(name);
+        locations.push(isExpression ? `式「${name}」` : `変数${name}`);
         if (props.initialVariables[name].toString() === props.currentVariables[name].toString()) {
           hintText += hintText ? '\n\n' : '\n\nヒント: ';
           hintText +=
@@ -234,7 +234,7 @@ export const BoardEditor = forwardRef<TurtleGraphicsHandle, TurtleGraphicsProps>
             <Table size="sm">
               <Thead>
                 <Tr>
-                  <Th>変数名</Th>
+                  <Th>変数/式</Th>
                   <Th>値（=や+=などの代入がないと変化しない）</Th>
                 </Tr>
               </Thead>
diff --git a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/ProblmBody.tsx b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/ProblmBody.tsx
index 31e97a32..b4e6170f 100644
--- a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/ProblmBody.tsx
+++ b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/ProblmBody.tsx
@@ -317,11 +317,10 @@ function getInitialVariables(
   let adjustedPreviousTraceItemIndex = previousTraceItemIndex;
 
   if (problemType === 'step') {
-    while (
-      adjustedPreviousTraceItemIndex > 0 &&
-      traceItems[currentTraceItemIndex].depth !== traceItems[adjustedPreviousTraceItemIndex].depth
-    ) {
-      if (traceItems[currentTraceItemIndex].depth > traceItems[adjustedPreviousTraceItemIndex].depth) {
+    const currentDepth = traceItems[currentTraceItemIndex].depth;
+    while (adjustedPreviousTraceItemIndex > 0 && currentDepth !== traceItems[adjustedPreviousTraceItemIndex].depth) {
+      if (currentDepth > traceItems[adjustedPreviousTraceItemIndex].depth) {
+        // 過去のトレースの方が現在のトレースよりも深いため。
         return getEmptyVariables(currentVariables);
       }
       adjustedPreviousTraceItemIndex--;
@@ -330,6 +329,7 @@ function getInitialVariables(
     if (
       traceItems[currentTraceItemIndex].callStack.at(-1) !== traceItems[adjustedPreviousTraceItemIndex].callStack.at(-1)
     ) {
+      // 過去のトレースと現在のトレースのスタックトレースが別であるため。
       return getEmptyVariables(currentVariables);
     }
   }
diff --git a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/Variables.tsx b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/Variables.tsx
index 8b2a4c0d..b99c7caf 100644
--- a/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/Variables.tsx
+++ b/src/app/(withAuth)/courses/[courseId]/lectures/[lectureId]/problems/[problemId]/Variables.tsx
@@ -25,7 +25,7 @@ export const Variables: React.FC<VariablesProps> = ({ traceItemVars }) => {
         <Table>
           <Thead>
             <Tr>
-              <Th>変数名</Th>
+              <Th>変数/式</Th>
               <Th isNumeric w="0">
                 値
               </Th>
diff --git a/src/app/(withAuth)/usage/page.tsx b/src/app/(withAuth)/usage/page.tsx
index 187ab774..0b77201d 100644
--- a/src/app/(withAuth)/usage/page.tsx
+++ b/src/app/(withAuth)/usage/page.tsx
@@ -40,7 +40,7 @@ const CoursesPage: NextPage = async () => {
         <Image alt="Turtle Movement" my={4} src="/images/usage_03.png" />
 
         <Text mt={16}>
-          ④盤面の下に「変数名」「値」と書かれたフォームがある場合は、プログラムを実行した時の最終的な変数の値を入力してください。
+          ④盤面の下に「変数/式」「値」と書かれたフォームがある場合は、プログラムを実行した時の最終的な変数の値を入力してください。
         </Text>
         <Image alt="Variable Input" my={4} src="/images/usage_04.png" />
 
diff --git a/src/problems/instantiateProblem.ts b/src/problems/instantiateProblem.ts
index 7ca51e3b..a96b3804 100644
--- a/src/problems/instantiateProblem.ts
+++ b/src/problems/instantiateProblem.ts
@@ -15,6 +15,11 @@ export type InstantiatedProblem = {
    */
   displayProgram: string;
 
+  /**
+   * The program to be executable via `eval()`. For debugging.
+   */
+  executableCode: string;
+
   /**
    * The trace items of the program.
    */
diff --git a/src/problems/problemData.ts b/src/problems/problemData.ts
index 3433ec4b..096ca5ca 100644
--- a/src/problems/problemData.ts
+++ b/src/problems/problemData.ts
@@ -90,7 +90,8 @@ export const problemIds = [
   'string5',
   'oop1',
   'oop2',
-  'oop3',
+  'static2',
+  'polymorphism1',
   'test1',
   'test2',
   'test3',
@@ -197,7 +198,8 @@ export const problemIdToName: Record<ProblemId, string> = {
   string5: '文字列を使おう(5)',
   oop1: 'オブジェクト指向プログラミング(1)',
   oop2: 'オブジェクト指向プログラミング(2)',
-  oop3: 'オブジェクト指向プログラミング(3)',
+  static2: '静的フィールド(2)',
+  polymorphism1: 'ポリモルフィズム(1)',
   test1: 'ステップ実行のテスト用問題(1)',
   test2: 'ステップ実行のテスト用問題(2)',
   test3: 'ステップ実行のテスト用問題(3)',
@@ -242,8 +244,8 @@ export const courseIdToLectureIndexToProblemIds: Record<CourseId, ProblemId[][]>
     ['method1', 'method2', 'method3', 'method4', 'method5', 'return1', 'return2', 'return3', 'return4', 'return5'],
     ['array1', 'array2', 'array3', 'array4', 'array5', 'string1', 'string2', 'string3', 'string4', 'string5'],
   ],
-  tuBeginner2: [['oop1', 'oop2', 'oop3']],
-  test: [['test1', 'test2', 'test3', 'test4', 'test5']],
+  tuBeginner2: [],
+  test: [['test1', 'test2', 'test3', 'test4', 'test5', 'oop1', 'oop2', 'static2', 'polymorphism1']],
 };
 
 export const courseIdToLectureIds: Record<CourseId, string[]> = JSON.parse(
@@ -253,7 +255,7 @@ export const courseIdToLectureIds: Record<CourseId, string[]> = JSON.parse(
 export const problemIdToLanguageIdToProgram: Record<ProblemId, Record<LanguageId, string>> = {
   straight: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
     `.trim(),
@@ -269,7 +271,7 @@ public class Main {
   },
   straight2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.forward();
@@ -287,7 +289,7 @@ public class Main {
   },
   stepBack: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.backward();
     `.trim(),
@@ -303,7 +305,7 @@ public class Main {
   },
   stepBack2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.backward();
@@ -325,7 +327,7 @@ public class Main {
   },
   turnRight: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.turnRight();
 t.forward();
@@ -343,7 +345,7 @@ public class Main {
   },
   turnRight2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.turnRight();
@@ -365,7 +367,7 @@ public class Main {
   },
   turnLeftAndRight: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.turnRight();
 t.forward();
 t.turnLeft();
@@ -385,7 +387,7 @@ public class Main {
   },
   turnLeftAndRight2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.turnRight();
 t.forward();
@@ -407,7 +409,7 @@ public class Main {
   },
   turnLeftAndRight3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.turnRight();
 t.forward();
 t.turnLeft();
@@ -431,7 +433,7 @@ public class Main {
   },
   turnLeftAndRight4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.turnRight();
@@ -459,7 +461,7 @@ public class Main {
   },
   square1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.turnRight();
 t.forward();
@@ -481,7 +483,7 @@ public class Main {
   },
   square2: {
     instrumented: `
-const t = new Turtle(<1-5>, <1-4>);
+const t = new Turtle(<1-5>, <1-4>); // trace
 t.forward();
 t.turnRight();
 t.forward();
@@ -503,7 +505,7 @@ public class Main {
   },
   square3: {
     instrumented: `
-const t = new Turtle(<2-5>, <2-5>);
+const t = new Turtle(<2-5>, <2-5>); // trace
 t.forward();
 t.turnLeft();
 t.forward();
@@ -529,7 +531,7 @@ public class Main {
   },
   square4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.turnRight();
@@ -565,7 +567,7 @@ public class Main {
   variable: {
     instrumented: `
 s.set('x', <1-5>);
-const t = new Turtle(s.get('x'), <1-5>);
+const t = new Turtle(s.get('x'), <1-5>); // trace
 t.forward();
  `.trim(),
     java: `
@@ -582,7 +584,7 @@ public class Main {
     instrumented: `
 s.set('a', <2-6>);
 s.set('a', s.get('a') - 1);
-const t = new Turtle(<1-5>, s.get('a'));
+const t = new Turtle(<1-5>, s.get('a')); // trace
 t.forward();
  `.trim(),
     java: `
@@ -601,7 +603,7 @@ public class Main {
 s.set('x', <1-4>);
 s.set('x', s.get('x') + 1);
 s.set('y', s.get('x') + 1);
-const t = new Turtle(s.get('x'), s.get('y'));
+const t = new Turtle(s.get('x'), s.get('y')); // trace
 t.forward();
 `.trim(),
     java: `
@@ -621,7 +623,7 @@ public class Main {
 s.set('b', <1-4>);
 s.set('b', s.get('b') + 1);
 s.set('a', s.get('b') - 2);
-const t = new Turtle(s.get('a') + 1, s.get('b'));
+const t = new Turtle(s.get('a') + 1, s.get('b')); // trace
 t.forward();
 `.trim(),
     java: `
@@ -642,7 +644,7 @@ s.set('x', <1-5>);
 s.set('x', s.get('x') - 1);
 s.set('y', s.get('x') * 2);
 s.set('y', s.get('y') / 3);
-const t = new Turtle(s.get('x') + 1, s.get('y') + 1);
+const t = new Turtle(s.get('x') + 1, s.get('y') + 1); // trace
 t.forward();
 `.trim(),
     java: `
@@ -663,7 +665,7 @@ public class Main {
 s.set('a', <1-3>);
 s.set('b', s.get('a') * 2);
 s.set('c', s.get('b') - 2);
-const t = new Turtle(s.get('c'), s.get('b'));
+const t = new Turtle(s.get('c'), s.get('b')); // trace
 t.forward();
 `.trim(),
     java: `
@@ -684,7 +686,7 @@ s.set('x', <0-2>);
 s.set('y', (s.get('x') * 2) + 1);
 s.set('z', (s.get('y') * 2) + (s.get('x') / 2));
 s.set('x', s.get('z') / 3);
-const t = new Turtle(s.get('x'), s.get('y'));
+const t = new Turtle(s.get('x'), s.get('y')); // trace
 t.forward();
     `.trim(),
     java: `
@@ -707,7 +709,7 @@ s.set('y', (s.get('x') * 3) + 2);
 s.set('z', (s.get('y') * 2) - (s.get('x') * 3));
 s.set('x', (s.get('z') / 4) % 7);
 s.set('y', (s.get('x') + s.get('y')) % 7);
-const t = new Turtle(s.get('x'), s.get('y'));
+const t = new Turtle(s.get('x'), s.get('y')); // trace
 t.backward();
     `.trim(),
     java: `
@@ -731,7 +733,7 @@ s.set('y', (s.get('x') * 4) + 3);
 s.set('z', (s.get('y') * 3) - (s.get('x') * 2));
 s.set('x', ((s.get('z') / 5) + s.get('x')) % 7);
 s.set('y', ((s.get('x') * 2) + s.get('y')) % 7);
-const t = new Turtle(s.get('x'), s.get('y'));
+const t = new Turtle(s.get('x'), s.get('y')); // trace
 t.forward();
     `.trim(),
     java: `
@@ -756,7 +758,7 @@ s.set('z', (s.get('y') * 2) - (s.get('x') * 3));
 s.set('w', (s.get('z') + s.get('x')) % 5);
 s.set('x', ((s.get('z') / 6) + s.get('w')) % 7);
 s.set('y', ((s.get('x') * 3) + s.get('y')) % 7);
-const t = new Turtle(s.get('x'), s.get('y'));
+const t = new Turtle(s.get('x'), s.get('y')); // trace
 t.forward();
     `.trim(),
     java: `
@@ -776,7 +778,7 @@ public class Main {
   },
   while1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('i', 0);
 while (s.get('i') < <3-5>) {
   t.forward();
@@ -798,7 +800,7 @@ public class Main {
   },
   while2: {
     instrumented: `
-const t = new Turtle(<0-1>, <0-1>);
+const t = new Turtle(<0-1>, <0-1>); // trace
 s.set('i', <1-2>);
 while (s.get('i') < <4-6>) {
   t.forward();
@@ -820,7 +822,7 @@ public class Main {
   },
   while3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('i', 0);
 while (s.get('i') < <2-3>) {
   s.set('i', s.get('i') + 1);
@@ -844,7 +846,7 @@ public class Main {
   },
   while4: {
     instrumented: `
-const t = new Turtle(<0-1>, <0-1>);
+const t = new Turtle(<0-1>, <0-1>); // trace
 t.turnRight();
 s.set('i', <1-2>);
 while (s.get('i') < <4-5>) {
@@ -872,7 +874,7 @@ public class Main {
   },
   while5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('i', <1-2>);
 while (s.get('i') < <3-4>) {
   t.forward();
@@ -900,7 +902,7 @@ public class Main {
   },
   for1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <3-5>; s.set('i', s.get('i') + 1)) {
   t.forward();
 }
@@ -919,7 +921,7 @@ public class Main {
   },
   for2: {
     instrumented: `
-const t = new Turtle(<1-2>, <1-2>);
+const t = new Turtle(<1-2>, <1-2>); // trace
 for (s.set('i', <1-2>); s.get('i') < <4-6>; s.set('i', s.get('i') + 1)) {
   t.forward();
 }
@@ -938,7 +940,7 @@ public class Main {
   },
   for3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('i', 0);
 for (; s.get('i') < <2-3>;) {
   t.forward();
@@ -962,7 +964,7 @@ public class Main {
   },
   for4: {
     instrumented: `
-const t = new Turtle(<1-2>, <1-2>);
+const t = new Turtle(<1-2>, <1-2>); // trace
 s.set('i', 1);
 for (; s.get('i') < <3-4>;) {
   t.forward();
@@ -994,7 +996,7 @@ for (s.set('i', 2); s.get('i') <= <4-5>; s.set('i', s.get('i') + 1)) {
 }
 delete s.vars['i'];
 s.set('x', s.get('x') / 3);
-const t = new Turtle(s.get('x') + 1, 0);
+const t = new Turtle(s.get('x') + 1, 0); // trace
 t.forward();
     `.trim(),
     java: `
@@ -1022,7 +1024,7 @@ for (s.set('i', <4-5>); s.get('i') > 0; s.set('i', s.get('i') - 1)) {
 delete s.vars['i'];
 s.set('a', s.get('a') / 4);
 s.set('b', s.get('b') / 5);
-const t = new Turtle(s.get('a') % 6, s.get('b') % 6);
+const t = new Turtle(s.get('a') % 6, s.get('b') % 6); // trace
 t.forward();
     `.trim(),
     java: `
@@ -1044,7 +1046,7 @@ public class Main {
   },
   for7: {
     instrumented: `
-const t = new Turtle(3, 3);
+const t = new Turtle(3, 3); // trace
 s.set('sum', 0);
 for (s.set('i', 1); s.get('i') <= <4-6>; s.set('i', s.get('i') + 1)) {
   s.set('sum', s.get('sum') + s.get('i'));
@@ -1080,7 +1082,7 @@ public class Main {
   },
   doubleLoop1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <2-3>; s.set('i', s.get('i') + 1)) {
   for (s.set('j', 0); s.get('j') < <2-3>; s.set('j', s.get('j') + 1)) {
       t.forward();
@@ -1106,7 +1108,7 @@ public class Main {
   },
   doubleLoop2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.turnRight();
 for (s.set('i', 0); s.get('i') < <2-3>; s.set('i', s.get('i') + 1)) {
   for (s.set('j', 0); s.get('j') < <2-3>; s.set('j', s.get('j') + 1)) {
@@ -1134,7 +1136,7 @@ public class Main {
   },
   doubleLoop3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', <3-4>); s.get('i') > 0; s.set('i', s.get('i') - 1)) {
   for (s.set('j', 0); s.get('j') < s.get('i'); s.set('j', s.get('j') + 1)) {
     t.forward();
@@ -1160,7 +1162,7 @@ public class Main {
   },
   doubleLoop4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', <3-4>); s.get('i') > 0; s.set('i', s.get('i') - 1)) {
   s.set('j', s.get('i'));
   while (s.get('j') >= 0) {
@@ -1190,7 +1192,7 @@ public class Main {
   },
   doubleLoop5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <3-4>; s.set('i', s.get('i') + 1)) {
   for (s.set('j', <0-1>); s.get('j') <= s.get('i'); s.set('j', s.get('j') + 1)) {
     t.forward();
@@ -1225,7 +1227,7 @@ public class Main {
   },
   if1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <7-9>; s.set('i', s.get('i') + 1)) {
   t.forward();
   if (s.get('i') % 3 === 2) {
@@ -1250,7 +1252,7 @@ public class Main {
   },
   if2: {
     instrumented: `
-const t = new Turtle(<1-2>, <1-2>);
+const t = new Turtle(<1-2>, <1-2>); // trace
 t.turnRight();
 for (s.set('i', 0); s.get('i') < <6-8>; s.set('i', s.get('i') + 1)) {
   t.forward();
@@ -1277,7 +1279,7 @@ public class Main {
   },
   if3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <4-5>; s.set('i', s.get('i') + 1)) {
   t.forward();
   if (s.get('i') % 2 === 0) {
@@ -1306,7 +1308,7 @@ public class Main {
   },
   if4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <4-5>; s.set('i', s.get('i') + 1)) {
   t.forward();
   if (s.get('i') % 3 === 0) {
@@ -1335,7 +1337,7 @@ public class Main {
   },
   if5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <3-4>; s.set('i', s.get('i') + 1)) {
   for (s.set('j', 0); s.get('j') < <2-3>; s.set('j', s.get('j') + 1)) {
     if (s.get('j') % 2 === 0) {
@@ -1371,7 +1373,7 @@ public class Main {
   },
   elseIf1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <4-6>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') < 2) {
     t.forward();
@@ -1401,7 +1403,7 @@ public class Main {
   },
   elseIf2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <5-7>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') % 4 === 0) {
     t.forward();
@@ -1435,7 +1437,7 @@ public class Main {
   },
   elseIf3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 7; s.set('i', s.get('i') + 1)) {
   if (s.get('i') < 2) {
     t.forward();
@@ -1469,7 +1471,7 @@ public class Main {
   },
   elseIf4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <6-7>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') % 5 === 0) {
     t.forward();
@@ -1503,7 +1505,7 @@ public class Main {
   },
   elseIf5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <7-8>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') % 5 === 1) {
     t.turnRight();
@@ -1533,7 +1535,7 @@ public class Main {
   },
   switch1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <5-7>; s.set('i', s.get('i') + 1)) {
   switch (s.get('i')) {
     case 0: case 1:
@@ -1566,7 +1568,7 @@ public class Main {
   },
   switch2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <5-7>; s.set('i', s.get('i') + 1)) {
   switch (s.get('i') % 4) {
     case 1:
@@ -1599,7 +1601,7 @@ public class Main {
   },
   switch3: {
     instrumented: `
-const t = new Turtle(2, 2);
+const t = new Turtle(2, 2); // trace
 for (s.set('i', 0); s.get('i') < <6-7>; s.set('i', s.get('i') + 1)) {
   switch (s.get('i')) {
     case 0:
@@ -1646,7 +1648,7 @@ public class Main {
   },
   switch4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <7-8>; s.set('i', s.get('i') + 1)) {
   switch (s.get('i') % 5) {
     case 0:
@@ -1689,7 +1691,7 @@ public class Main {
   },
   switch5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <9-10>; s.set('i', s.get('i') + 1)) {
   switch (s.get('i') % 6) {
     case 0:
@@ -1734,7 +1736,7 @@ public class Main {
   },
   break1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 while (true) {
   if (!t.canMoveForward()) break;
   t.forward();
@@ -1754,7 +1756,7 @@ public class Main {
   },
   break2: {
     instrumented: `
-const t = new Turtle(<3-4>,<3-4>);
+const t = new Turtle(<3-4>,<3-4>); // trace
 while (true) {
   if (!t.canMoveForward()) break;
   t.forward();
@@ -1784,7 +1786,7 @@ public class Main {
   },
   break3: {
     instrumented: `
-const t = new Turtle(<4-6>, <4-6>);
+const t = new Turtle(<4-6>, <4-6>); // trace
 for (s.set('i', 0); s.get('i') < 4; s.set('i', s.get('i') + 1)) {
   while (true) {
     t.forward();
@@ -1811,7 +1813,7 @@ public class Main {
   },
   break4: {
     instrumented: `
-const t = new Turtle(<3-5>, <3-5>);
+const t = new Turtle(<3-5>, <3-5>); // trace
 for (s.set('i', 0); s.get('i') < 3; s.set('i', s.get('i') + 1)) {
   while (true) {
     if (!t.canMoveForward()) break;
@@ -1838,7 +1840,7 @@ public class Main {
   },
   break5: {
     instrumented: `
-const t = new Turtle(<4-6>, <4-6>);
+const t = new Turtle(<4-6>, <4-6>); // trace
 for (s.set('i', 0); s.get('i') < 3; s.set('i', s.get('i') + 1)) {
   for (s.set('j', 0); s.get('j') < 6; s.set('j', s.get('j') + 1)) {
     if (!t.canMoveForward()) break;
@@ -1876,7 +1878,7 @@ public class Main {
   },
   continue1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <3-5>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') == 0) {
     continue;
@@ -1901,7 +1903,7 @@ public class Main {
   },
   continue2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <5-7>; s.set('i', s.get('i') + 1)) {
   if (s.get('i') % <2-3> == 1) {
     t.turnRight();
@@ -1928,7 +1930,7 @@ public class Main {
   },
   continue3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 2; s.set('i', s.get('i') + 1)) {
   for (s.set('j', s.get('i') * 4); s.get('j') < 8; s.set('j', s.get('j') + 1)) {
     if (s.get('j') % 4 == 1) {
@@ -1964,7 +1966,7 @@ public class Main {
   },
   continue4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 3; s.set('i', s.get('i') + 1)) {
   for (s.set('j', s.get('i')); s.get('j') < 6; s.set('j', s.get('j') + 1)) {
     if (s.get('j') % 2 == 0) {
@@ -2000,7 +2002,7 @@ public class Main {
   },
   continue5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 3; s.set('i', s.get('i') + 1)) {
   for (s.set('j', s.get('i') + 1); s.get('j') < 6; s.set('j', s.get('j') + 1)) {
     if (s.get('j') % 4 == 0) {
@@ -2038,7 +2040,7 @@ public class Main {
   },
   method1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(forwardTwoSteps, 't')(t);
 t.turnRight();
 call(threeStepsForward, 't')(t);
@@ -2076,7 +2078,7 @@ public class Main {
   },
   method2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(forwardTwoSteps, 't')(t);
 call(turnAround, 't')(t);
 t.forward();
@@ -2095,7 +2097,7 @@ function turnAround(t) {
     java: `
 public class Main {
     public static void main(String[] args) {
-        Turtle t = new Turtle(); // sid:
+        Turtle t = new Turtle(); // sid
         二歩前に進める(t); // caller
         後ろを向く(t); // caller
         t.前に進む(); // sid
@@ -2113,7 +2115,7 @@ public class Main {
   },
   method3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(forwardGivenSteps, 't', 'n')(t, <3-4>);
 t.turnRight();
 call(forwardGivenSteps, 't', 'n')(t, 2);
@@ -2144,7 +2146,7 @@ public class Main {
   },
   method4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(forwardTwoSteps, 't')(t);
 t.turnRight();
 call(forwardFourSteps, 't')(t);
@@ -2180,7 +2182,7 @@ public class Main {
   },
   method5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(drawSquare, 't')(t);
 t.backward();
 t.backward();
@@ -2214,7 +2216,7 @@ public class Main {
   },
   return1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('x', call(double, 'a')(<2-3>));
 call(forwardGivenSteps, 't', 'n')(t, s.get('x'));
 
@@ -2249,7 +2251,7 @@ public class Main {
   },
   return2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('x', call(double, 'a')(2));
 call(forwardGivenSteps, 't', 'n')(t, s.get('x'));
 t.turnRight();
@@ -2290,7 +2292,7 @@ public class Main {
   },
   return3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 call(forwardGivenSteps, 't', 'n')(t, call(add, 'a', 'b')(1, 1));
 call(forwardGivenSteps, 't', 'n')(t, call(add, 'a', 'b')(1, 2));
 
@@ -2325,7 +2327,7 @@ public class Main {
   },
   return4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < <3-4>; s.set('i', s.get('i') + 1)) {
   if (call(isEven, 'a')(s.get('i'))) {
     t.turnRight();
@@ -2376,7 +2378,7 @@ public class Main {
   },
   return5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 3; s.set('i', s.get('i') + 1)) {
   for (s.set('j', 0); s.get('j') < 3; s.set('j', s.get('j') + 1)) {
     if (call(isEqual, 'a', 'b')(s.get('i'), s.get('j')))
@@ -2425,7 +2427,7 @@ public class Main {
 
   array1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('arr', [2, <1-2>, <1-2>]);
 for (s.set('i', 0); s.get('i') < s.get('arr').length; s.set('i', s.get('i') + 1)) {
   call(forwardGivenSteps, 't', 'n')(t, s.get('arr')[s.get('i')]);
@@ -2460,7 +2462,7 @@ public class Main {
   },
   array2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('arr', [<4-5>, <3-4>, <3-4>]);
 for (s.set('i', 0); s.get('i') < s.get('arr').length; s.set('i', s.get('i') + 1)) {
   call(forwardGivenSteps, 't', 'n')(t, s.get('arr')[s.get('i')]);
@@ -2495,7 +2497,7 @@ public class Main {
   },
   array3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('arr', [0, 1, 0, 2, 0]);
 for (s.set('i', 0); s.get('i') < s.get('arr').length; s.set('i', s.get('i') + 1)) {
   switch (s.get('arr')[s.get('i')]) {
@@ -2530,7 +2532,7 @@ public class Main {
   },
   array4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('arr', [0, 1, 0, 2, 0]);
 for (const cmd of [0, 1, 0, 2, 0]) {
   s.set('cmd', cmd);
@@ -2566,7 +2568,7 @@ public class Main {
   },
   array5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('arr', [0, 1, 0, 2, 0, 3, 0]);
 s.set('steps', 1);
 for (const cmd of [0, 1, 0, 2, 0, 3, 0]) {
@@ -2615,7 +2617,7 @@ public class Main {
   },
   string1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('s', 'frflf');
 for (s.set('i', 0); s.get('i') < s.get('s').length; s.set('i', s.get('i') + 1)) {
   switch (s.get('s').charAt(s.get('i'))) {
@@ -2650,7 +2652,7 @@ public class Main {
   },
   string2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('s', 'ffbrfl');
 for (s.set('i', 0); s.get('i') < s.get('s').length; s.set('i', s.get('i') + 1)) {
   switch (s.get('s').charAt(s.get('i'))) {
@@ -2689,7 +2691,7 @@ public class Main {
   },
   string3: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('s', 'frflf');
 for (const ch of 'frflf') {
   s.set('ch', ch);
@@ -2725,7 +2727,7 @@ public class Main {
   },
   string4: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('cmds', ['ri', 'aa', 'fo']);
 for (const cmd of ['ri', 'aa', 'fo']) {
   s.set('cmd', cmd);
@@ -2760,7 +2762,7 @@ public class Main {
   },
   string5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 s.set('cmds', ['ri', 'add', 'fo', 'add', 'le', 'fo', 'fo']);
 s.set('x', 0);
 for (const cmd of ['ri', 'add', 'fo', 'add', 'le', 'fo', 'fo']) {
@@ -2816,8 +2818,8 @@ public class Main {
   },
   oop1: {
     instrumented: `
-const t1 = new Turtle(1, 1);
-const t2 = new Turtle(3, 3);
+const t1 = new Turtle(1, 1); // trace
+const t2 = new Turtle(3, 3); // trace
 t1.forward();
 t2.forward();
 t1.forward();
@@ -2837,21 +2839,23 @@ public class Main {
 `.trim(),
   },
   oop2: {
+    // 上のコードから下にあるクラスを参照するためには、main()関数を定義しないといけない。
     instrumented: `
 function main() {
-  const m = new MyTurtle(0, 0, 2);
-  m.forward();
+  const m = call(MyTurtle, 'x', 'y', 'speed')(0, 0, 2);
+  call(m.forward.bind(m))();
 }
 
 class MyTurtle {
   constructor(x, y, speed) {
-    this.speed = speed;
-    this.c = new Turtle(x, y);
+    this.speed = speed; // trace
+    this.c = new Turtle(x, y); // trace
   }
   forward() {
-    for (let i = 0; i < this.speed; i++) {
+    for (s.set('i', 0); s.get('i') < this.speed; s.set('i', s.get('i') + 1)) {
       this.c.forward();
     }
+    delete s.vars['i'];
   }
 }
 
@@ -2860,8 +2864,8 @@ main();
     java: `
 public class Main {
   public static void main(String[] args) {
-    MyTurtle m = new MyTurtle(0, 0, 2); // sid
-    m.forward(); // sid
+    MyTurtle m = new MyTurtle(0, 0, 2); // caller
+    m.forward(); // caller
   }
 }
 
@@ -2880,21 +2884,160 @@ class MyTurtle {
 }
 `.trim(),
   },
-  oop3: {
+  // ----------- 初級プログラミングⅡ 第1回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第1回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第2回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第2回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第3回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第3回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第4回 ここから -----------
+  static2: {
+    // グローバル変数を扱う際は、 `myGlobal` という名前のオブジェクトを使うこと。
+    // 上のコードから下にあるクラスを参照するためには、main()関数を定義しないといけない。
     instrumented: `
-const t = new Turtle();
-`,
+myGlobal.Settings = { speed: 3 };
+
+function main() {
+  const t1 = call(MyTurtle)(); // trace
+  call(t1.moveForward.bind(t1))();
+  myGlobal.Settings.speed = 2; // trace
+  const t2 = call(MyTurtle)(); // trace
+  call(t1.moveForward.bind(t1))();
+  call(t2.moveForward.bind(t2))();
+}
+
+class MyTurtle {
+  constructor() {
+    this.t = new Turtle();
+  }
+  moveForward() {
+    for (s.set('i', 0); s.get('i') < myGlobal.Settings.speed; s.set('i', s.get('i') + 1)) {
+      this.t.forward();
+    }
+    delete s.vars['i'];
+  }
+}
+
+main();
+`.trim(),
     java: `
 public class Main {
   public static void main(String[] args) {
-    Turtle c = new Turtle(); // sid
+    MyTurtle t1 = new MyTurtle(); // caller // sid
+    t1.moveForward(); // caller
+    Settings.speed = 2; // sid
+    MyTurtle t2 = new MyTurtle(); // caller // sid
+    t1.moveForward(); // caller
+    t2.moveForward(); // caller
   }
 }
-`,
+
+class Settings {
+  static public int speed = 3;
+}
+
+class MyTurtle {
+  private Turtle t = new Turtle();
+
+  void moveForward(Turtle t) {
+    for (int i = 0; i < Settings.speed; i++) { // sid
+      t.前に進む(); // sid
+    }
+  }
+}
+`.trim(),
+  },
+  // ----------- 初級プログラミングⅡ 第4回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第5回 ここから -----------
+  polymorphism1: {
+    instrumented: `
+function main() {
+  const ts = [call(MyTurtle, 'x', 'y')(0, 0), call(FastTurtle, 'p')(1)]; // trace
+  for (s.set('i', 0); s.get('i') < ts.length; s.set('i', s.get('i') + 1)) {
+    call(ts[s.get('i')].drawLine.bind(ts[s.get('i')]))();
+  }
+}
+
+class MyTurtle {
+  constructor(x, y) {
+    this.t = new Turtle(x, y);
+  }
+  drawLine() {
+    for (s.set('i', 0); s.get('i') < this.length(); s.set('i', s.get('i') + 1)) {
+      this.t.forward();
+    }
+    delete s.vars['i'];
+  }
+  length() {
+    return 2;
+  }
+}
+
+class FastTurtle extends MyTurtle {
+  constructor(p) {
+    super(p, p);
+  }
+  length() {
+    return 3;
+  }
+}
+
+main();
+`.trim(),
+    java: `
+public class Main {
+  public static void main(String[] args) {
+    MyTurtle[] ts = {
+        new MyTurtle(0, 0), new FastTurtle(1) };  // caller // sid
+    for (int i = 0; i < ts.length; i++) {
+      ts[i].drawLine(); // caller
+    }
+  }
+}
+
+class MyTurtle {
+  Turtle t;
+
+  MyTurtle(int x, int y) {
+    this.t = new Turtle(x, y);
+  }
+  void drawLine() {
+    for (int i = 0; i < this.length(); i++) { // sid
+      this.t.前に進む(); // sid
+    }
+  }
+  int length() {
+    return 2;
+  }
+}
+
+class FastTurtle extends MyTurtle {
+  FastTurtle(int p) {
+    super(p, p);
+  }
+  @Override int length() {
+    return 3;
+  }
+}
+`.trim(),
   },
+  // ----------- 初級プログラミングⅡ 第5回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第6回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第6回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第7回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第7回 ここまで -----------
+
+  // ----------- 初級プログラミングⅡ 第8回 ここから -----------
+  // ----------- 初級プログラミングⅡ 第8回 ここまで -----------
   test1: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.forward();
@@ -2913,7 +3056,7 @@ public class Main {
   },
   test2: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 for (s.set('i', 0); s.get('i') < 2; s.set('i', s.get('i') + 1)) {
   t.forward();
   t.forward();
@@ -2968,13 +3111,13 @@ public class Main {
   },
   test4: {
     instrumented: `
-const t1 = new Turtle();
+const t1 = new Turtle(); // trace
 t1.forward();
 t1.turnRight();
 s.set('i', 0);
 t1.forward();
 
-const t2 = new Turtle(2, 3, 'G');
+const t2 = new Turtle(2, 3, 'G'); // trace
 t2.forward();
 s.set('foo', 'あいうえお');
 s.set('bar', <1-100>);
@@ -3004,7 +3147,7 @@ public class Main {
   },
   test5: {
     instrumented: `
-const t = new Turtle();
+const t = new Turtle(); // trace
 t.forward();
 t.forward();
 t.turnRight();
diff --git a/src/problems/traceProgram.ts b/src/problems/traceProgram.ts
index 784699ac..d785da31 100644
--- a/src/problems/traceProgram.ts
+++ b/src/problems/traceProgram.ts
@@ -4,11 +4,12 @@ import {
   TURTLE_GRAPHICS_DEFAULT_COLOR as DEFAULT_COLOR,
   TURTLE_GRAPHICS_EMPTY_COLOR as EMPTY_COLOR,
 } from '../constants';
-import type { CellColor, ColorChar } from '../types';
 
 import type { InstantiatedProblem } from './instantiateProblem';
 import type { LanguageId } from './problemData';
 
+import type { CellColor, ColorChar } from '@/types';
+
 export interface TurtleTrace {
   x: number;
   y: number;
@@ -21,6 +22,7 @@ export interface TurtleTrace {
 export interface TraceItem {
   depth: number;
   sid: number;
+  /** caller id のスタック。 `// caller` のある行に caller id が付与される。 */
   callStack: number[];
   vars: TraceItemVariable;
   turtles: TurtleTrace[];
@@ -47,6 +49,7 @@ export const colorToChar = Object.fromEntries(
 ) as Record<CellColor, ColorChar>;
 
 export function traceProgram(
+  this: unknown,
   instrumented: string,
   rawDisplayProgram: string,
   languageId: LanguageId
@@ -59,37 +62,17 @@ export function traceProgram(
       throw new Error('Instrumented program MUST NOT contain variable declarations.');
     }
   }
-
-  let statementId = 1;
-  let callerId = 1;
-  const modifiedCodeLines = [];
-  for (const line of instrumented.split('\n')) {
-    let statementReplaced = false;
-    let callReplaced = false;
-    const newLine = line
-      .replace(/for\s*\(([^;]*);\s*([^;]*);/, (_, init, cond) => `for (${init}; checkForCond(${cond}, ${statementId});`)
-      .replaceAll(
-        /(new\s+Turtle|\.set|\.forward|\.backward|\.turnRight|\.turnLeft)\(([^\n;]*)\)(;|\)\s*{)/g,
-        (_, newOrMethod, args, tail) => {
-          statementReplaced = true;
-          const delimiter = args === '' ? '' : ', ';
-          return `${newOrMethod}(${statementId}${delimiter}${args})${tail}`;
-        }
-      )
-      .replaceAll('call(', (_) => {
-        callReplaced = true;
-        return `call(${callerId}, `;
-      });
-    if (statementReplaced) statementId++;
-    if (callReplaced) callerId++;
-    modifiedCodeLines.push(newLine);
-  }
+  const modifiedCodeLines = modifyCode(instrumented);
   const modifiedCode = modifiedCodeLines.join('\n');
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const thisPropNames = Object.keys((this as any) || {});
   // 無理に難読化する必要はないが、コードの文量を減らす意識を持つ。
   const executableCode = `
+let myGlobal = {};
 const trace = [];
 const turtles = [];
 const callStack = [];
+const thisPropNames = ${JSON.stringify(thisPropNames)};
 let s;
 class Scope {
   constructor(parent) {
@@ -102,9 +85,9 @@ class Scope {
     }
     throw new Error(\`\${varName} is not defined: \${JSON.stringify(s)}\`);
   }
-  set(sid, varName, value) {
+  set(sid, self, varName, value) {
     this.vars[varName] = typeof value === 'number' ? Math.floor(value) : value;
-    addTrace(sid);
+    addTrace(sid, self);
   }
   enterNewScope(params) {
     s = new Scope(this);
@@ -131,16 +114,15 @@ const dx = [0, 1, 0, -1];
 const dy = [1, 0, -1, 0];
 const board = Array.from({length: ${GRID_ROWS}}, () => Array.from({length: ${GRID_COLUMNS}}, () => '${EMPTY_COLOR}'));
 class Turtle {
-  constructor(sid, x = 0, y = 0, color = '${DEFAULT_COLOR}') {
+  constructor(x = 0, y = 0, color = '${DEFAULT_COLOR}') {
     this.x = x;
     this.y = y;
     this.color = color;
     this.dir = 'N';
     board[this.y][this.x] = this.color;
     turtles.push(this);
-    addTrace(sid);
   }
-  forward(sid) {
+  forward(sid, self) {
     const index = dirs.indexOf(this.dir);
     this.x += dx[index];
     this.y += dy[index];
@@ -148,9 +130,9 @@ class Turtle {
       throw new Error(\`Out of bounds: (\${this.x}, \${this.y})\`);
     }
     board[this.y][this.x] = this.color;
-    addTrace(sid);
+    addTrace(sid, self);
   }
-  backward(sid) {
+  backward(sid, self) {
     const index = dirs.indexOf(this.dir);
     this.x -= dx[index];
     this.y -= dy[index];
@@ -158,7 +140,7 @@ class Turtle {
       throw new Error(\`Out of bounds: (\${this.x}, \${this.y})\`);
     }
     board[this.y][this.x] = this.color;
-    addTrace(sid);
+    addTrace(sid, self);
   }
   canMoveForward() {
     const index = dirs.indexOf(this.dir);
@@ -166,17 +148,34 @@ class Turtle {
     const ny = this.y + dy[index];
     return nx >= 0 && nx < ${GRID_COLUMNS} && ny >= 0 && ny < ${GRID_ROWS};
   }
-  turnRight(sid) {
+  turnRight(sid, self) {
     this.dir = dirs[(dirs.indexOf(this.dir) + 1) % 4];
-    addTrace(sid);
+    addTrace(sid, self);
   }
-  turnLeft(sid) {
+  turnLeft(sid, self) {
     this.dir = dirs[(dirs.indexOf(this.dir) + 3) % 4];
-    addTrace(sid);
+    addTrace(sid, self);
   }
 }
-function addTrace(sid) {
-  trace.push({depth: s.getDepth(), sid, callStack: [...callStack], turtles: turtles.map(t => ({...t})), vars: {...s.vars}, board: board.map(r => r.join('')).join('\\n')});
+function addTrace(sid, self) {
+  const vars = {...s.vars, ...myGlobal};
+  if (self && self !== globalThis) {
+    vars['this'] = {...self};
+    for (const name of thisPropNames) delete vars['this'][name];
+  }
+  flattenObjects(vars);
+  trace.push({depth: s.getDepth(), sid, callStack: [...callStack], turtles: turtles.map(t => ({...t})), vars, board: board.map(r => r.join('')).join('\\n')});
+}
+function flattenObjects(obj) {
+  for (const [key, value] of Object.entries(obj)) {
+    if (value instanceof Turtle) delete obj[key];
+    else if (value && typeof value === 'object' && !Array.isArray(value)) {
+      delete obj[key];
+      for (const [nestKey, nestValue] of Object.entries(value)) {
+        if (!(nestValue instanceof Turtle)) obj[\`\${key}.\${nestKey}\`] = nestValue;
+      }
+    }
+  }
 }
 function checkForCond(cond, sid) {
   if (!cond && trace.at(-1).sid === sid) {
@@ -187,18 +186,21 @@ function checkForCond(cond, sid) {
 function call(cid, f, ...argNames) {
   return (...argValues) => {
     if (argNames.length !== argValues.length) {
-      throw new Error(\`Expected \${argNames.length} arguments, got \${argValues.length}.\`);
+      throw new Error(\`Expected \${argNames.length} arguments (\${argNames}), got \${argValues.length} (\${argValues}). Fix call() in instrumented code.\`);
     }
     try {
       callStack.push(cid);
       s.enterNewScope(argNames.map((n, i) => [n, argValues[i]]).filter(([n, v]) => !(v instanceof Turtle)));
-      return f(...argValues);
+      return isClass(f) ? new f(...argValues) : f(...argValues);
     } finally {
       callStack.pop();
       s.leaveScope();
     }
   };
 }
+function isClass(obj) {
+  return typeof obj === 'function' && /^class\\s/.test(obj.toString());
+}
 trace.push({depth: 0, sid: 0, callStack: [], turtles: [], vars: {}, board: board.map(r => r.join('')).join('\\n')});
 s = new Scope();
 ${modifiedCode.trim()}
@@ -236,9 +238,43 @@ ${modifiedCode.trim()}
   return {
     languageId,
     displayProgram: refinedLines.join('\n'),
+    executableCode,
     traceItems: trace,
     sidToLineIndex,
     callerIdToLineIndex,
     finalVars,
   };
 }
+
+function modifyCode(instrumented: string): string[] {
+  const modifiedCodeLines = [];
+  let statementId = 1;
+  let callerId = 1;
+  for (const line of instrumented.split('\n')) {
+    let statementReplaced = false;
+    let callReplaced = false;
+    const newLine = line
+      // Python向けに最後のループの処理かどうかを判定するために checkForCond を挿入する。
+      .replace(/for\s*\(([^;]*);\s*([^;]*);/, (_, init, cond) => `for (${init}; checkForCond(${cond}, ${statementId});`)
+      .replaceAll(
+        /(\.set|\.forward|\.backward|\.turnRight|\.turnLeft)\(([^\n;]*)\)(;|\)\s*{)/g,
+        (_, newOrMethod, args, tail) => {
+          statementReplaced = true;
+          const delimiter = args === '' ? '' : ', ';
+          return `${newOrMethod}(${statementId}, this${delimiter}${args})${tail}`;
+        }
+      )
+      .replace(/\s*\/\/\s*trace\s*/, (_) => {
+        statementReplaced = true;
+        return `addTrace(${statementId}, this);`;
+      })
+      .replaceAll('call(', (_) => {
+        callReplaced = true;
+        return `call(${callerId}, `;
+      });
+    if (statementReplaced) statementId++;
+    if (callReplaced) callerId++;
+    modifiedCodeLines.push(newLine);
+  }
+  return modifiedCodeLines;
+}
diff --git a/test.js b/test.js
new file mode 100644
index 00000000..632d0197
--- /dev/null
+++ b/test.js
@@ -0,0 +1,175 @@
+const trace = [];
+const turtles = [];
+const callStack = [];
+const thisPropNames = ['charToColor', 'colorToChar', 'traceProgram'];
+let s;
+class Scope {
+  constructor(parent) {
+    this.parent = parent;
+    this.vars = {};
+  }
+  get(varName) {
+    if (this.vars[varName] !== undefined) {
+      return this.vars[varName];
+    }
+    throw new Error(`${varName} is not defined: ${JSON.stringify(s)}`);
+  }
+  set(sid, self, varName, value) {
+    this.vars[varName] = typeof value === 'number' ? Math.floor(value) : value;
+    addTrace(sid, self);
+  }
+  enterNewScope(params) {
+    s = new Scope(this);
+    for (const [k, v] of params) {
+      s.vars[k] = v;
+    }
+  }
+  leaveScope() {
+    if (!this.parent) throw new Error();
+    s = this.parent;
+  }
+  getDepth() {
+    let depth = 0;
+    let currentScope = this;
+    while (currentScope.parent) {
+      depth++;
+      currentScope = currentScope.parent;
+    }
+    return depth;
+  }
+}
+const dirs = ['N', 'E', 'S', 'W'];
+const dx = [0, 1, 0, -1];
+const dy = [1, 0, -1, 0];
+const board = Array.from({ length: 7 }, () => Array.from({ length: 7 }, () => '.'));
+class Turtle {
+  constructor(x = 0, y = 0, color = '#') {
+    this.x = x;
+    this.y = y;
+    this.color = color;
+    this.dir = 'N';
+    board[this.y][this.x] = this.color;
+    turtles.push(this);
+  }
+  forward(sid, self) {
+    const index = dirs.indexOf(this.dir);
+    this.x += dx[index];
+    this.y += dy[index];
+    if (this.x < 0 || 7 <= this.x || this.y < 0 || 7 <= this.y) {
+      throw new Error(`Out of bounds: (${this.x}, ${this.y})`);
+    }
+    board[this.y][this.x] = this.color;
+    addTrace(sid, self);
+  }
+  backward(sid, self) {
+    const index = dirs.indexOf(this.dir);
+    this.x -= dx[index];
+    this.y -= dy[index];
+    if (this.x < 0 || 7 <= this.x || this.y < 0 || 7 <= this.y) {
+      throw new Error(`Out of bounds: (${this.x}, ${this.y})`);
+    }
+    board[this.y][this.x] = this.color;
+    addTrace(sid, self);
+  }
+  canMoveForward() {
+    const index = dirs.indexOf(this.dir);
+    const nx = this.x + dx[index];
+    const ny = this.y + dy[index];
+    return nx >= 0 && nx < 7 && ny >= 0 && ny < 7;
+  }
+  turnRight(sid, self) {
+    this.dir = dirs[(dirs.indexOf(this.dir) + 1) % 4];
+    addTrace(sid, self);
+  }
+  turnLeft(sid, self) {
+    this.dir = dirs[(dirs.indexOf(this.dir) + 3) % 4];
+    addTrace(sid, self);
+  }
+}
+function addTrace(sid, self) {
+  const vars = { ...s.vars, ...(typeof myGlobal !== 'undefined' && myGlobal) };
+  if (self && self !== globalThis) {
+    vars['this'] = { ...self };
+    for (const name of thisPropNames) delete vars['this'][name];
+  }
+  flattenObjects(vars);
+  trace.push({
+    depth: s.getDepth(),
+    sid,
+    callStack: [...callStack],
+    turtles: turtles.map((t) => ({ ...t })),
+    vars,
+    board: board.map((r) => r.join('')).join('\n'),
+  });
+}
+function flattenObjects(obj) {
+  for (const [key, value] of Object.entries(obj)) {
+    if (value instanceof Turtle) delete obj[key];
+    else if (value && typeof value === 'object' && !Array.isArray(value)) {
+      delete obj[key];
+      for (const [nestKey, nestValue] of Object.entries(value)) {
+        if (!(nestValue instanceof Turtle)) obj[`${key}.${nestKey}`] = nestValue;
+      }
+    }
+  }
+}
+function checkForCond(cond, sid) {
+  if (!cond && trace.at(-1).sid === sid) {
+    trace.at(-1).last = true;
+  }
+  return cond;
+}
+function call(cid, f, ...argNames) {
+  return (...argValues) => {
+    if (argNames.length !== argValues.length) {
+      throw new Error(
+        `Expected ${argNames.length} arguments (${argNames}), got ${argValues.length} (${argValues}). Fix call() in instrumented code.`
+      );
+    }
+    try {
+      callStack.push(cid);
+      s.enterNewScope(argNames.map((n, i) => [n, argValues[i]]).filter(([n, v]) => !(v instanceof Turtle)));
+      return isClass(f) ? new f(...argValues) : f(...argValues);
+    } finally {
+      callStack.pop();
+      s.leaveScope();
+    }
+  };
+}
+function isClass(obj) {
+  return typeof obj === 'function' && /^class\s/.test(obj.toString());
+}
+trace.push({ depth: 0, sid: 0, callStack: [], turtles: [], vars: {}, board: board.map((r) => r.join('')).join('\n') });
+s = new Scope();
+myGlobal = { Settings: { speed: 3 } };
+
+function main() {
+  const t1 = call(1, MyTurtle)();
+  addTrace(1, this);
+  call(2, t1.moveForward.bind(t1))();
+  myGlobal.Settings.speed = 2;
+  addTrace(2, this);
+  const t2 = call(3, MyTurtle)();
+  addTrace(3, this);
+  call(4, t1.moveForward.bind(t1))();
+  call(5, t2.moveForward.bind(t2))();
+}
+
+class MyTurtle {
+  constructor() {
+    this.t = new Turtle();
+  }
+  moveForward() {
+    for (
+      s.set(4, this, 'i', 0);
+      checkForCond(s.get('i') < myGlobal.Settings.speed, 4);
+      s.set(4, this, 'i', s.get('i') + 1)
+    ) {
+      this.t.forward(5, this);
+    }
+    delete s.vars['i'];
+  }
+}
+
+main();
+console.log({ trace, finalVars: { ...s.vars } });
diff --git a/tests/unit/traceProgram.test.ts b/tests/unit/traceProgram.test.ts
index 316412d2..48513805 100644
--- a/tests/unit/traceProgram.test.ts
+++ b/tests/unit/traceProgram.test.ts
@@ -595,6 +595,19 @@ public class Straight {
   }
 );
 
+test('Trace a specific program', () => {
+  const problem = instantiateProblem('static2', 'java', '');
+  if (!problem) throw new Error('Failed to generate problem.');
+
+  const { displayProgram, executableCode, sidToLineIndex, traceItems } = problem;
+  console.info('---------------------- displayProgram ----------------------\n', displayProgram);
+  console.info('------------------------------------------------------------\n');
+  console.info('---------------------- executableCode ----------------------\n', executableCode);
+  console.info('------------------------------------------------------------\n');
+  console.info('sidToLineIndex:', JSON.stringify(Object.fromEntries(sidToLineIndex), undefined, 2));
+  console.info('traceItems:', JSON.stringify(traceItems, undefined, 2));
+});
+
 /**
  * テストに失敗した際に、WebStorm上で期待値との差異を確認しやすくするために、文字列化しておく。
  */