Java 8 Predicate example

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Java 8 predicate is functional interface introduced in java 8.

Predicate definition

Predicate is single argument functional interface which returns true or false. It takes one argument and returns result in form of true or false.

Here is the definition of Predicate interface.

Predicate methods example

test()

This is abstract method of Predicate interface. It evaluates true if predicate matches the input argument.

Here is simple example of test() method which checks if input argument is greater than 100 or not.

Output:

is 200 greater than 100: true

You can pass Predicate as a function argument too.

and()

and() is default method which returns composite predicate that denotes logical AND of this predicate and passed predicate.

Output:

200 lies between 100 and 300: true

We have created two predicates and checked logical AND between predicate1 and predicate2

or()

or() is default method which returns composite predicate that denotes logical OR of this predicate and passed predicate.

Output:

(30 > 100) or (30 < 50) returns: true

We have created two predicates and checked logical or between predicate1 and predicate2

negate()

negate() is default method which returns predicate that denotes logical negation of this predicate.

Output:

30 is less than 100: true

We have created two predicates and checked logical or between predicate1 and predicate2

isEqual()

isEqual() is static method returns predicate that compares if two arguments are equal based on object’s equals() method.

Output:

true
false
  • predicate.test("test1") returns true because it matches with "test1" passed to isEqual method
  • predicate.test("test2") returns false because it does not match with "test1" passed to isEqual method

Please note that above comparison is done on the basis of String’s equals() method.

Filter list using Predicate

Java 8 stream’s filter method takes Predicate as a argument and can be used to filter the list with the help of predicates.
Lets say you have student class as below:

Lets create a function which will be used to filter students based on predicates.

Lets create a main class as below:

When you run above program, you will get below output:

18 are :[Student [id=1, name=Arpit, gender=M, age=19], Student [id=4, name=Martin, gender=M, age=21]]

Female students having age < 18 are :[Student [id=3, name=Mary, gender=F, age=14], Student [id=5, name=Monica, gender=F, age=16]]

That’s all about Java 8 Predicate example

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