Java 13 - Switch Expressions (JEP 354)
Enhancements for switch expressions are introduced in JDK 12 as a preview feature (JEP 325). Java 13's JEP 354 extends this switch expressions by adding a new yield keyword to return a value from switch expression. That means, a switch expression that returning a value should use yield, and a switch statement that not returning a value should use break.
Here the example of switch expression with break to return value in JDK 12:
Java12SwitchCaseBreak.java
public class Java12SwitchCaseBreak {
public static void main(String[] args) {
getGrade('A');
getGrade('C');
getGrade('D');
getGrade('E');
getGrade('X');
}
public static void getGrade(char grade) {
System.out.print(switch (grade) {
case 'A':
break "Excellent";
case 'B':
break "Good";
case 'C':
break "Standard";
case 'D':
break "Low";
case 'E':
break "Very Low";
default:
break "Invalid";
});
System.out.println(getResult(grade));
}
public static String getResult(char grade) {
return switch (grade) {
case 'A', 'B', 'C':
break "::Success";
case 'D', 'E':
break "::Fail";
default:
break "::No result";
};
}
}
In JDK 13, you need to use yield, instead of break.
Java13SwitchCaseBreak.java
public class Java13SwitchCaseBreak {
public static void main(String[] args) {
getGrade('A');
getGrade('C');
getGrade('D');
getGrade('E');
getGrade('X');
}
public static void getGrade(char grade) {
System.out.print(switch (grade) {
case 'A': yield "Excellent";
case 'B': yield "Good";
case 'C': yield "Standard";
case 'D': yield "Low";
case 'E': yield "Very Low";
default: yield "Invalid";
});
System.out.println(getResult(grade));
}
public static String getResult(char grade) {
return switch (grade) {
case 'A', 'B', 'C' -> "::Success";
case 'D', 'E' -> "::Fail";
default -> "::No result";
};
}
}
As you can see return values using arrows from Java 12 switch expression is still supported:
return switch (grade) { case 'A', 'B', 'C' -> "::Success"; case 'D', 'E' -> "::Fail"; default -> "::No result"; };
Switch expressions are a preview feature and are disabled by default. You need to enable it by using --enable-preview option.
# compile javac --enable-preview <other flags> <source files> # run java --enable-preview <other flags> <main class>
See also: Java 12 - Switch Expressions, which contains section on how to enable preview flag in maven-compiler-plugin. Or if using gradle, in your build.gradle file:
tasks.withType(JavaCompile).each { it.options.compilerArgs.add('--enable-preview') } test { jvmArgs(['--enable-preview']) }
Desson AriawanProgrammer