SwitchExpressionExample.java

public class SwitchExpressionExample {
    public static void main(String ... args) {
        compatibleWithOldVersion();

		longVersion();
		shortVersion();

		switchWithReturn();

		inferringType();
    }

	public static void compatibleWithOldVersion() {
		int luckNumber = 7;

		// we can use the old syntax (case:)
        var wasLucky = switch (luckNumber) {
			// here the fall-through happens (if there is no break or return the next case will be executed)
            case 7:
				break false; // break was changed to yield in Java 13
            case 13:
				break true;
			// here we must provide a default case (compiler checks exhaustiveness)
			default:
				throw new IllegalArgumentException("Wrong number");
        }; // switch expression needs ;

        System.out.println("\nWas I lucky? " + wasLucky);
	}

	public static void longVersion() {
		var mood = Incomes.Good;

		// arrow syntax with no fall-through (only the arrow block will be executed)
		var shouldIGo = switch (mood) {
			// accepts multiple case labels
			case Good, Regular -> {
				break true;
			}
			case Bad -> {
				break false;
			}
			// there is no need to use default (we covered all possible cases)
		};

		System.out.println("\nShould I go? " + shouldIGo);
	}

	public static void shortVersion() {
		var mood = Incomes.Good;

		// cool syntax with no fall-through (only the arrow block will be executed)
		var shouldIGo = switch (mood) {
			// accepts multiple case labels
			case Good, Regular -> true;
			case Bad -> false;
			// there is no need to use default (we covered all possible cases)
		};

		System.out.println("\nShould I go? " + shouldIGo);
	}

	public static void switchWithReturn() {
		var mood = Incomes.Bad;

		// used as statement (there is no assign)
		switch (mood) {
			case Good -> {
				var easy = true;
				System.out.println("\nKeep working");
			}
			case Regular, Bad -> {
				// we can now declare vars with same name (each arrow has its own scope)
				var easy = true;
				System.out.println("\nGo home");
				/*
				 * we can only return inside a block and when switch
				 * is used as statement
				 */
				return;
			}
		}
	}

	public static void inferringType() {
		var mood = Incomes.Good;

		// compiler infers the most specific supertype
		// of String and IllegalArgumentException is Serializable
		// Serializable whichType // we can only use its supertype
		var whichType = switch (mood) {
			case Good -> "All right";
			default -> new IllegalArgumentException("Not right");
		};

		// won't work
		// System.out.println("What is the length? " + whichType.length());
	}
}

enum Incomes {
	Good,
	Regular,
	Bad
}