improved examples of switch expression in Java 14;

Author: wesleyegberto

README.md

@@ -14,6 +14,8 @@ A project to explore more about the new features of Java 8, 9, ...
   * Virtual Thread :rocket:
   * Pattern matching for `switch` (preview 3)
   * Vector API (fourth incubator)
+  * Record pattern
+  * Structured concurrency
 
 * [Java 18](java-18/) (Mar, 2022)
   * UTF-8 by Default
@@ -24,6 +26,7 @@ A project to explore more about the new features of Java 8, 9, ...
 
 * [Java 17](java-17/) (Sep, 2021)
   * Sealed classes (standard)
+  * Pattern matching for `switch` (preview)
   * Enhanced Pseudo-Random Number Generator
   * Deprecate the Applet API for Removal
   * New macOS rendering for Java 2D API

java-12/SwitchExpressionExample.java

@@ -86,7 +86,7 @@ public static void inferringType() {
 		var mood = Incomes.Good;
 
 		// compiler infers the most specific supertype
-		// of String and IllegalArgumentException = Serializable
+		// of String and IllegalArgumentException is Serializable
 		// Serializable whichType // we can only use its supertype
 		var whichType = switch (mood) {
 			case Good -> "All right";

java-13/SwitchExpressionTests.java

@@ -1,5 +1,5 @@
-/*
- * Same example from Java 12 but with syntax update.
+/**
+ * Same example from Java 12 but with syntax update (changed `break` to `yield`).
  */
 public class SwitchExpressionTests {
     public static void main(String ... args) {

java-14/SwitchExpressions.java

@@ -5,6 +5,10 @@
 public class SwitchExpressions {
 	public static void main(String[] args) {
 		// Now switch expressions are final o/
+		// kinds of switch case statements
+		System.out.println(oldWay(Mood.BAD));
+		System.out.println(lambdaWay(Mood.GOOD));
+		System.out.println(mixingSwitchKinds(Mood.REGULAR));
 
 		FeaturePhase switchWithPatternMatching = FeaturePhase.FINAL;
 
@@ -15,9 +19,77 @@ public static void main(String[] args) {
 
 		System.out.println("Switch expressions with pattern matching: " + message);
 	}
+
+	 static String oldWay(Mood mood) {
+		// old way (set a var or return method value)
+		switch (mood) {
+			// we use lambda here, swith isn't used in a statement
+			// error: not a statement
+			// case GOOD -> "All right";
+
+			// can mix kinds of switch
+			// error: different case kinds used in the switch
+			// case GOOD -> { return "All right"; }
+
+			case GOOD: return "All right";
+			case REGULAR: return "Can do better";
+			default: return "Let's improve!";
+		}
+	}
+
+	static String lambdaWay(Mood mood) {
+		return switch (mood) {
+			case GOOD -> {
+				// yield can only be used in a switch statement
+				yield "All right";
+			}
+			// lambda without block requires semi-colon
+			case REGULAR -> "Can do better";
+			default -> "Let's improve!";
+		};
+	}
+
+	static String mixingSwitchKinds(Mood mood) {
+		String message;
+		switch (mood) {
+			// here we can return because isn't a switch statement
+			case BAD -> {
+				return "Not today";
+			}
+			// we still can change vars
+			default -> {
+				message = "We still can go";
+			}
+		}
+
+		// switch used in a statement
+		var result = switch (mood) {
+			// we cannot mix return here (will cause `not a statement` in the following cases)
+
+			case GOOD -> {
+				// we cannot return when switch is used as statement
+				// error: attempt to return out of a switch expression
+				// return "All right";
+				yield "All right";
+			}
+
+			// can mix kinds of switch
+			// error: different case kinds used in the switch
+			// default: return "Still can improve";
+
+			default -> "Still can improve";
+		};
+		return result;
+	}
 }
 
 enum FeaturePhase {
 	PREVIEW,
 	FINAL
-}
+}
+
+enum Mood {
+	GOOD,
+	REGULAR,
+	BAD
+}