Predicate interface

Predicate accepts an argument and returns a boolean value. Predicate functional interface in Java is a type of function that accepts a single argument and returns a boolean (True/ False). It provides the functionality of filtering, it filter a stream components on the base of a provided predicate.

Predicate Interface Methods.

1. boolean test(T t)
- The Predicate test() method returns true if the input argument matches the predicate, otherwise false.

Example of Predicate test method

public static void main(String[] args) { 
    Predicate<Integer> pr = a -> (a > 10);

     // Calling Predicate method  
    System.out.println(pr.test(20));       
} 

Output:
    true
     

2. static Predicate isEqual(Object targetRef)
- The Predicate isEqual() method is a static method of the Predicate interface that is used to test the equality of two objects. The object can be a string, integer, or a class object.

Example of Predicate isEqual method

public static void main(String[] args) {  
 Predicate<String> pr = 
    Predicate.isEqual( "MyAllText" );

 // Calling Predicate method  
 System.out.println(
    pr.test("AllText")
 ); 
 // Calling Predicate method  
 System.out.println(
    pr.test("MyAllText")
 );
 // Calling Predicate method  
 System.out.println(
    pr.test("MyAll")
 );   

}

Output:
false
true
false

3. default Predicate and(Predicate other)
- The Predicate and() method is used to compose two expression(lambda) that represents a short-circuiting logical AND of this predicate. It can be uses to perform logical operations by combining two lambda expressions. See the example below. Here, we used and() method to check whether a number lies between two numeric range or not.

Example of Predicate and method

public static void main(String[] args) {   
  Predicate<Integer> pr1 = 
    x -> (x > 20);

  Predicate<Integer> pr2 = 
    x -> (x < 80);

  // Calling Predicate method  
  System.out.println(
    pr1.and(pr2).test(100)
  ); 
  // Calling Predicate method  
  System.out.println(
    pr1.and(pr2).test(50)
  ); 
  // Calling Predicate method  
  System.out.println(
    pr1.and(pr2).test(10)
  );
}

Output:
    false
    true
    false

4. default Predicate negate()
- The Predicate negate() method allows invert the result of a Predicate. It returns a predicate that represents the logical negation of this predicate.

Example of Predicate negate method

public static void main (String[] args) {
  Predicate<String> startsWithCharJ = 
    s -> s.startsWith("H");
  Predicate<String> hasLengthOfInt5 = 
    s -> s.length() == 5;

  // Calling without negate method 
  System.out.println(
    startsWithCharJ.test("Horse")
  ); 
  // Calling without negate method 
  System.out.println(
    hasLengthOfInt5
    .test("India")
  ); 

  Predicate<String> negateStartsWithCharJ = 
    startsWithCharJ.negate();
  Predicate<String> negatehasLengthOfInt5 = 
    hasLengthOfInt5.negate();

  // Calling after negate predicate 
  System.out.println(
    negateStartsWithCharJ
    .test("Horse")
  ); 
  // Calling after negate predicate 
  System.out.println(
  negatehasLengthOfInt5
    .test("India")
  ); 

}

Output:
    true
    true
    false
    false

5. or(Predicate other)
- The Predicate or() method works similarly to and(), but it returns true if either of the any Predicates return true.

Example of Predicate or method

public static void main (String[] args) { 
  Predicate<String> startsWithCharH = 
    s -> s.startsWith( "H" );
 
  Predicate<String> hasLengthOfInt5 = 
    s -> s.length() == 5;

  Predicate<String> startsWithCharHOrHasLengthOf5 = 
    startsWithCharH.or(hasLengthOfInt5);

  System.out.println( 
    startsWithCharHOrHasLengthOf5
    .test( "Hero" )
  ); 
  System.out.println(
    startsWithCharHOrHasLengthOf5
    .test( "India" )
  ); 
  System.out.println(
    startsWithCharHOrHasLengthOf5
    .test( "Method" )
  );

}  

Output:
    true
    true
    false

Bi-Predicate

Bi-Predicate is also an extension of the Predicate functional interface, which, instead of one, takes two arguments, does some processing, and returns the boolean value.