[break] Stop using Matcher.group() which allocates a string (#466)

Parsing all types of sls version no longer involves allocating strings just to parse them as integers again.

build.gradle

@@ -44,7 +44,7 @@ subprojects {
     apply plugin: 'org.inferred.processors'
 
     tasks.check.dependsOn(javadoc)
-    sourceCompatibility = 1.8
+    sourceCompatibility = 11
 
     tasks.withType(JavaCompile) {
         options.compilerArgs += ['-Werror']

changelog/@unreleased/pr-466.v2.yml

@@ -0,0 +1,6 @@
+type: break
+break:
+  description: This library now requires Java 11+ (previously it could run on Java
+    8+). This allows us to eliminate some String allocations from parsing SLS versions.
+  links:
+  - https://github.com/palantir/sls-version-java/pull/466

sls-versions/src/main/java/com/palantir/sls/versions/MatchResult.java

@@ -26,15 +26,24 @@ interface MatchResult {
     int groupCount();
 
     final class RegexMatchResult implements MatchResult {
+        private static final int RADIX = 10;
+        private final String string;
         private final Matcher matcher;
 
-        RegexMatchResult(Matcher matcher) {
+        RegexMatchResult(String string, Matcher matcher) {
+            this.string = string;
             this.matcher = matcher;
         }
 
         @Override
         public int groupAsInt(int group) {
-            return Integer.parseInt(matcher.group(group));
+            int groupStart = matcher.start(group);
+            int groupEnd = matcher.end(group);
+            if (groupStart == -1) {
+                throw new NumberFormatException();
+            }
+
+            return Integer.parseUnsignedInt(string, groupStart, groupEnd, RADIX);
         }
 
         @Override

sls-versions/src/main/java/com/palantir/sls/versions/RegexParser.java

@@ -43,7 +43,7 @@ static RegexParser of(String regex) {
     @Nullable
     public MatchResult tryParse(String string) {
         Matcher matcher = pattern.matcher(string);
-        return matcher.matches() ? new MatchResult.RegexMatchResult(matcher) : null;
+        return matcher.matches() ? new MatchResult.RegexMatchResult(string, matcher) : null;
     }
 
     @Override