Introduction

• Predicate interface is a functional interface in Java 8 that represents a boolean-valued function (a condition or test) of one argument.
• It is part of the java.util.function package.

• Uses of Predicate Interface:
  • Used to test conditions on objects.
  • Used to filter elements in collections.
  • Can combine multiple conditions using and(), or(), and negate().
  • Helps write clean, functional-style code using lambda expressions.

• Syntax :

  public interface Predicate
  {
      boolean test(T t);
      //some default methods are also present
  }

Programs:

• 1. Simple program without lambda expression:

  import java.util.function.Predicate;
  
  public class MainApp
  {
      public static void main(String[] args)
      {
          // Predicate to check if a number is even using anonymous class
          Predicate<Integer> isEven = new Predicate<Integer>() {
              @Override
              public boolean test(Integer x) {
                  return x % 2 == 0;
              }
          };
  
          // Test numbers
          System.out.println("Is 4 is even : " + isEven.test(4));
          System.out.println("Is 7 is even : " + isEven.test(7));
      }
  }

  Output:

  Is 4 is even : true
  Is 7 is even : false

• 2. Program with lambda expression:

  import java.util.function.Predicate;
  
  public class MainApp
  {
      public static void main(String[] args)
      {
          // Predicate to check if a number is even using lambda expression
          Predicate<Integer> isEven = x -> x % 2 == 0;
  
          // Test numbers
          System.out.println("Is 4 even? " + isEven.test(4));
          System.out.println("Is 7 even? " + isEven.test(7));
      }
  }

  Output:

  Is 4 is even : true
  Is 7 is even : false