Java 12 – Switch Expressions

By mkyong | Updated: September 19, 2019

Viewed: 5,332 (+70 pv/w)

Tags: java java 12 new features switch

Java 12, JEP 325: Switch Expressions enhanced the traditional switch statement to support the following new features:

• Multiple case labels
• Switch expression returning value via break (replaced with yield in Java 13 switch expressions)
• Switch expression returning value via label rules (arrow)

P.S Switch expressions are a preview feature and are disabled by default.

A traditional switch example.

package com.mkyong.java12;

public class JEP325 {

    public static void main(String[] args) {

        System.out.println(getTextBefore12(1));
        System.out.println(getTextBefore12(3));
        System.out.println(getTextBefore12(6));
        System.out.println(getTextBefore12(10));

    }

    // Traditional switch statement
    private static String getTextBefore12(int number) {
        String result = "";
        switch (number) {
            case 1:
            case 2:
                result = "one or two";
                break;
            case 3:
                result = "three";
                break;
            case 4:
            case 5:
            case 6:
                result = "four or five or six";
                break;
            default:
                result = "unknown";
        };
        return result;
    }

}

Output

one or two
three
four or five or six
unknown

1. Multiple case labels

Now, we can declares multiple cases with comma-separated labels.

    private static String getTextMultipleLabels(int number) {
        String result = "";
        switch (number) {
            case 1, 2:
                result = "one or two";
                break;
            case 3:
                result = "three";
                break;
            case 4, 5, 6:
                result = "four or five or six";
                break;
            default:
                result = "unknown";
        };
        return result;
    }

2. Return value via Break

Now, this switch is an expression (returning something), also called value breaks.

    private static String getTextViaBreak(int number) {
        String result = switch (number) {
            case 1:
            case 2:
                break "one or two"; 
            case 3:
                break "three";
            case 4:
            case 5:
            case 6:
                break "four or five or six";
            default:
                break "unknown";
        };
        return result;
    }

4. Return value via Arrow

We also can return value via arrow or label rules.

    private static String getTextViaArrow(int number) {
        String result = switch (number) {
            case 1, 2 -> "one or two";
            case 3 -> "three";
            case 4, 5, 6 -> "four or five or six";
            default -> "unknown";
        };
        return result;
    }

5. Enable preview features

5.1 A normal javac compile will prompts the following errors:

$ javac JEP325.java
JEP325.java:39: error: multiple case labels are a preview feature and are disabled by default.
            case 1, 2:
                    ^
  (use --enable-preview to enable multiple case labels)

JEP325.java:56: error: switch expressions are a preview feature and are disabled by default.
        String result = switch (number) {
                        ^
  (use --enable-preview to enable switch expressions)
JEP325.java:75: error: switch rules are a preview feature and are disabled by default.
            case 1, 2 -> "one or two";
                      ^
  (use --enable-preview to enable switch rules)
3 errors

5.2 We need to enable the preview feature manually:

javac --enable-preview --release 12 Example.java
java --enable-preview Example

References

• Java 13 – Switch Expressions
• OpenJDK 12 Project
• JEP 325: Switch Expressions
• JEP 305: Pattern Matching for instanceof
• JEP-354: Switch Expressions (Preview)
• Java version history