Java yield Keyword

The yield keyword in Java is used in the context of switch expressions, introduced in Java 12 as a preview feature and made a standard feature in Java 14. The yield keyword allows returning a value from a case block within a switch expression.

Table of Contents

1. Introduction
2. yield in Switch Expressions
   • Syntax
   • Examples
3. Real-World Use Case
4. Conclusion

Introduction

The yield keyword is used within a switch expression to return a value from a particular case. This enhances the switch statement by allowing it to be used as an expression that can return a value, making the code more concise and expressive.

yield in Switch Expressions

Syntax

The syntax for using the yield keyword in a switch expression is as follows:

var result = switch (expression) {
    case value1 -> value1Result;
    case value2 -> {
        // code block
        yield value2Result;
    }
    default -> defaultValue;
};

Example

To demonstrate the usage of the yield keyword in a switch expression, we will calculate a value based on the input using a switch expression.

public class YieldSwitchExample {
    public static void main(String[] args) {
        int day = 3;
        String dayType = switch (day) {
            case 1, 2, 3, 4, 5 -> "Weekday";
            case 6, 7 -> "Weekend";
            default -> {
                System.out.println("Invalid day");
                yield "Unknown";
            }
        };
        System.out.println("Day type: " + dayType);
    }
}

Output:

Day type: Weekday

Real-World Use Case

Mapping Enums to Descriptions

In real-world applications, the yield keyword can be used to map enum values to their corresponding descriptions using a switch expression.

Example

public class YieldRealWorldExample {
    enum TrafficLight {
        RED, YELLOW, GREEN
    }

    public static void main(String[] args) {
        TrafficLight signal = TrafficLight.RED;

        String action = switch (signal) {
            case RED -> "Stop";
            case YELLOW -> {
                System.out.println("Caution");
                yield "Slow Down";
            }
            case GREEN -> "Go";
        };

        System.out.println("Action: " + action);
    }
}

Output:

Action: Stop

Conclusion

The yield keyword in Java enhances switch expressions by allowing them to return values from individual case blocks. This makes the code more concise and expressive, providing a more flexible and powerful alternative to traditional switch statements. By understanding and using the yield keyword, you can write more modern and efficient Java code.