Java LongPredicate Interface with examples

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Welcome to Java 8 Series. In this tutorial, you will learn about the Java LongPredicate Interface with examples.

LongPredicate is a Functional interface introduced as part of Java 8. It is available in java.util.function package.

What is the use of LongPredicate?

This interface is mainly used for evaluating an input of type long and turns an output of type boolean. Consider a case where we need to write a lambda expression which accepts one input of long type and perform an operation on the input and return a boolean.

Example

public class StaticReference {
	public static void main(String[] args) {
		Operation ops = (long input) -> {
			if (input == 10) {
				return true;
			} else
				return false;
		};
		boolean result = ops.validate(10);
		System.out.println(result);
	}

	interface Operation {
		boolean validate(long input);
	}
}

When you look at the above example, we have a function interface with an abstract method which accepts an argument of type long return boolean value. So a lambda expression needs a target type which needs to be a functional interface and in this example, it is Operation interface.

Instead of creating our own function interface for this scenario, Java has provided us a LongPredicate interface. Let now see in-depth details on Java LongPredicate Interface with examples.

LongPredicate Interface

@FunctionalInterface
public interface LongPredicate

LongPredicate interface contains an operation that accepts an input argument of type long and returns a boolean value

It is a functional interface and the functional method istest(long)

Method description

boolean test(int value)
value - the input argument

Example of LongPredicate interface using lambda

public class StaticReference {
	public static void main(String[] args) {
		LongPredicate intPredicate = (long input) -> {
			if (input == 10) {
				return true;
			} else
				return false;
		};
		boolean result = intPredicate.test(10);
		System.out.println(result);
	}
}

Example of LongPredicate interface using a Method reference

public class StaticReference {
	public static void main(String[] args) {
		LongPredicate intPredicate = StaticReference::test;
		boolean result = intPredicate.test(10);
		System.out.println(result);
	}

	static boolean test(long input) {
		if (input == 10) {
			return true;
		} else
			return false;
	}
}

If you want to write a lambda expression with an input argument of type long and boolean result, please use Java LongPredicate interface.

References

Java 8 LongPredicate official documentation

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