In this blog post, I will be explaining how the Java 8 functional interface Predicate works. To know more about functional interfaces, you can refer this blog post.

The Predicate interface provides a method called test. This method accepts a parameter of any data type and returns a boolean.

Predicate method with Integer argument

Consider the following code snippet:

public class PredicateDemo {

public static void main(String[] args) { 
    Predicate<Integer> greaterThan8 = (input) -> input > 8; 
    System.out.println("4 is greater than 8 = "+greaterThan8.test(4)); 
    System.out.println("12 is greater than 8 = "+greaterThan8.test(12)); 
    }

}

Here, the Predicate.test method checks if the input number is greater than 8. So when the above code is executed, it will print the following output:

4 is greater than 8 = false
12 is greater than 8 = true

Predicate method with String argument

Consider the following code snippet:

import java.util.function.Predicate;

public class PredicateDemo {

public static void main(String[] args) { 
    Predicate<String> startsWithHello = (str) -> str.startsWith("Hello"); 
    System.out.println("Hello World starts with Hello = "+startsWithHello.test("Hello World")); 
    System.out.println("Test String starts with Hello = "+startsWithHello.test("Test String"));
}
}

Here, the Predicate.test method checks if the input String starts with the String “Hello”. So when the above code is executed, it will print the following output:

Hello World starts with Hello = true 
Test String starts with Hello = false

You can get the source code for this example along with the code for other Java 8 examples at the GitHub repository here.