Java 8 Predicate Interface

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In this tutorial, we will learn about Java 8 Predicate interface.

Java 8 Predicate Interface

Predicate Interface :-

Predicate ( java.util.function.Predicate ) is a functional interface that has one abstract method and three default method declared in it.

Abstract method :- 

boolean  test ( T  t ) :- The abstract method test ( T t ) is a functional method. It accepts one parameter as an argument and return boolean value. It represents a conditional operation, where a passed argument is tested against a specific value to give a boolean ( True or False ) result.

Default method :-  

  1. default  Predicate<T>  and ( Predicate <? super T > other ) :- It returns a predicate that represents short circuiting logical AND of this predicate ( predicate on which method is called ) and another ( passed as an argument ).
  2. default  Predicate<T>  or ( Predicate <? super T > other ) :- It returns a predicate that represents short circuiting logical OR of this predicate ( predicate on which method is called ) and another ( passed as an argument ).
  3. default  Predicate<T>  negate (  ) :- It returns a predicate that represents logical negation of this predicate ( predicate on which method is called ).

Reference :-  Predicate Interface JavaDocs 

Java 8 Stream API have four methods where Predicate interface are used as an argument, they are as follows :-

  1. Stream<T>  filter ( Predicate<? super T> predicate )
  2. boolean  anyMatch ( Predicate<? super T> predicate )
  3. boolean  allMatch ( Predicate<? super T> predicate )
  4. boolean  noneMatch ( Predicate<? super T> predicate )

There are three specialised ( primitive specific ) form of Java 8 Predicate interface, which can be used in case of int, long and double. They are as follows :-

  1. IntPredicate interface ( JavaDocs ) :- It represents a predicate that accepts one integer as an argument and returns boolean value.
  2. DoublePredicate interface ( JavaDocs ) :- It represents a predicate that accepts one double as an argument and returns boolean value.
  3. LongPredicate interface ( JavaDocs ) :- It represents a predicate that accepts one long as an argument and returns boolean value.

Example – 1 :- 

This example will show you, how to create and call different methods of a predicate interface.

  public static void main(String[] args){
 
    Predicate<Integer> predicate1 = ( x ) -> { if( x == 5 ){ return true; }
                                               else{ return false; }};
    // Example of test method
    boolean result = predicate1.test(5);
    System.out.println(result);
 
    // Example of negate method
    boolean result3 = (predicate1.negate()).test(5);
    System.out.println(result3);
 
    Predicate<Integer> predicate2 = ( x ) -> { if( x == 7 ){ return true; }
                                               else{ return false; }};
 
    // Example of and method
    boolean result1 = predicate1.and(predicate2).test(5);
    System.out.println(result1);
 
    // Example of or method
    boolean result2 = predicate1.or(predicate2).test(5);
    System.out.println(result2); 
  }  

Result :- 

true
false
false
true

Example – 2 :- 

In this example, we will filter the elements of a list by using stream’s filter() method. This method takes one predicate as an argument.

  public static void main(String[] args){
    List<String> names = new ArrayList<String>();
    names.add("Akash");
    names.add("Susane");
    names.add("Hugh");
    names.add("Kim");
 
    names.stream().filter( n -> "Hugh".equals(n)).forEach( n -> System.out.println("Name : " + n)); 
  }  

Result :- 

Name : Hugh

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