Java 14: switch expression and pattern matching for instanceof

wesleyegberto · wesleyegberto · commit 24aa3fc68816 · 2020-03-11T22:06:11.000-03:00
diff --git a/java-11/README.md b/java-11/README.md
@@ -46,4 +46,3 @@
 * [Oracle's Z GC](https://wiki.openjdk.java.net/display/zgc/Main)
 * [Replacements for deprecated JPMS modules with Java EE APIs](https://stackoverflow.com/questions/48204141/replacements-for-deprecated-jpms-modules-with-java-ee-apis/48204154#48204154)
 * [Scripting Java 11, Shebang And All](https://blog.codefx.org/java/scripting-java-shebang/)
-* 
diff --git a/java-14/PatternMatchingForInstanceOf.java b/java-14/PatternMatchingForInstanceOf.java
@@ -0,0 +1,78 @@
+public class PatternMatchingForInstanceOf {
+	public static void main(String[] args) {
+		Animal dog1 = new Dog("Bob");
+		Animal c = new Cat();
+
+		// Old verbose way
+		if (dog1 instanceof Dog) {
+			// A cast just to manipulate the specific type
+			Dog d1 = (Dog) dog1;
+			play(d1);
+		}
+
+		// New way
+		if (dog1 instanceof Dog d1) {
+			play(d1);
+		}
+		if (c instanceof Cat c1) {
+			play(c1);
+		}
+
+		Animal dog2 = new Dog("Bob");
+		System.out.println("\nAre both equal? " + dog1.equals(dog2));
+	}
+
+	static void play(Dog d) {
+		System.out.println("Playing with Dog...");
+		d.makeSound();
+	}
+
+	static void play(Cat c) {
+		System.out.println("Playing with Cat...");
+		c.makeSound();
+	}
+}
+
+class Animal {
+	void makeSound() {
+		System.out.println("Generic sound");
+	}
+}
+
+class Cat extends Animal {
+	void makeSound() {
+		System.out.println("Miau");
+	}
+}
+
+class Dog extends Animal {
+	// here we assume that are equal when they have the same name
+	private String name;
+
+	Dog(String name) {
+		this.name = name;
+	}
+
+	void makeSound() {
+		System.out.println("Au au");
+	}
+
+	/*
+	 * Old way where we need to cast after the `instanceof`.
+	 */
+	public boolean equalsOldWay(Object o) {
+		// need to check if is the same type
+		if (!(o instanceof Dog))
+			return false;
+		// then we cast to work with this type
+		Dog d1 = (Dog) o;
+		// only now we can performe our [business] logic to compare
+		return d1.name.equals(d1.name);
+	}
+
+	public boolean equals(Object o) {
+		// more straightforward
+		return (o instanceof Dog d1)
+			&& d1.name.equals(d1.name);
+	}
+}
diff --git a/java-14/README.md b/java-14/README.md
@@ -1,5 +1,7 @@
 # Java 14
 
+To run each example use: `java --enable-preview --source 14 <FileName.java>`
+
 ## Features
 
 ### Language
diff --git a/java-14/SwitchExpressions.java b/java-14/SwitchExpressions.java
@@ -0,0 +1,23 @@
+/**
+ * We can run with:
+ * java <FileName.java>
+ */
+public class SwitchExpressions {
+	public static void main(String[] args) {
+		// Now switch expressions are final o/
+
+		FeaturePhase switchWithPatternMatching = FeaturePhase.FINAL;
+
+		var message = switch (switchWithPatternMatching) {
+			case FINAL -> "No longer need to use `--preview`";
+			case PREVIEW -> "Still needs to use `--preview`";
+		};
+
+		System.out.println("Switch expressions with pattern matching: " + message);
+	}
+}
+
+enum FeaturePhase {
+	PREVIEW,
+	FINAL
+}
