Deep Dive into Java 8 Predicate Interface

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Predicate is a Functional Interface (an Interface with only one abstract method) that was introduced in Java 8 in the java.util.function package.

Method	Description	Return Type	Exceptions	Input Type	Added in JDK
`test(T t)`	Evaluates this predicate on the given argument.	`boolean`		`T`	Java 8
`and(Predicate<? super T> other)`	Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another.	`Predicate<T>`	`NullPointerException` if `other` is `null`	`T`	Java 8
`negate()`	Returns a predicate that represents the logical negation of this predicate.	`Predicate<T>`		N/A	Java 8
`or(Predicate<? super T> other)`	Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another.	`Predicate<T>`	`NullPointerException` if `other` is `null`	`T`	Java 8
`isEqual(Object targetRef)`	Returns a predicate that tests if two arguments are equal according to `Objects.equals(Object, Object)`.	`Predicate<T>`		`T`	Java 8
`not(Predicate<? super T> target)`	Returns a predicate that is the negation of the supplied predicate.	`Predicate<T>`	`NullPointerException` if `target` is `null`	`T`	Java 11

Note: and(), negate(), or(), not() and isEqual() are all default methods.

The test() is the abstract method that returns a boolean by predicting whether the performed condition is true or not for the provided generic type argument T.

Example:

    public static void main(String[] args) {

        Predicate<Integer> evenOrOdd = num -> num % 2 == 0;

        int testNumberForEvenOdd = 12;
        boolean isEven = evenOrOdd.test(testNumberForEvenOdd);
        System.out.println(testNumberForEvenOdd + " is Even: " + isEven);

    }

Output:

12 is Even: true

Official Java 8 Predicate Documentation:

test(T t): Evaluates this predicate on the given argument.
and(Predicate<? super T> other): Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another.
negate(): Returns a predicate that represents the logical negation of this predicate.
or(Predicate<? super T> other): Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another.
isEqual(Object targetRef): Returns a predicate that tests if two arguments are equal according to Objects.equals(Object, Object).
not(Predicate<? super T> target): Returns a predicate that is the negation of the supplied predicate.