UnaryOperator Interface in Java

Last Updated : 11 Jul, 2025
The UnaryOperator Interface<T> is a part of the java.util.function package which has been introduced since Java 8, to implement functional programming in Java. It represents a function which takes in one argument and operates on it. However what distinguishes it from a normal Function is that both its argument and return type are the same. Hence this functional interface which takes in one generic namely:-
  • T: denotes the type of the input argument to the operation
Hence the UnaryOperator<T> overloads the Function<T, T> type. So it inherits the following methods from the Function Interface: The lambda expression assigned to an object of UnaryOperator type is used to define its accept() which eventually applies the given operation on its argument.

Functions in UnaryOperator Interface

The UnaryOperator interface consists of the following functions:

1. identity()

This method returns a UnaryOperator which takes in one value and returns it. The returned UnaryOperator does not perform any operation on its only value. Syntax: 
static  UnaryOperator identity()
Parameters: This method does not take in any parameter. Returns: A UnaryOperator which takes in one value and returns it. Below is the code to illustrate accept() method: Program 1: Java 
import java.util.function.UnaryOperator;

public class GFG {
    public static void main(String args[])
    {

        // Instantiate the UnaryOperator interface
        UnaryOperator<Boolean>
            op = UnaryOperator.identity();

        // Apply identify() method
        System.out.println(op.apply(true));
    }
}
Output: 
true
Below are few examples to demonstrate the methods inherited from Function<T, T>: 1.accept() Java 
import java.util.function.Function;
import java.util.function.UnaryOperator;

public class GFG {
    public static void main(String args[])
    {
        UnaryOperator<Integer> xor = a -> a ^ 1;
        System.out.println(xor.apply(2));
    }
}
Output: 
3
2.addThen() Java 
import java.util.function.Function;
import java.util.function.UnaryOperator;

public class GFG {
    public static void main(String args[])
    {
        UnaryOperator<Integer> xor = a -> a ^ 1;
        UnaryOperator<Integer> and = a -> a & 1;
        Function<Integer, Integer> compose = xor.andThen(and);
        System.out.println(compose.apply(2));
    }
}
Output: 
1
3.compose() Java 
import java.util.function.Function;
import java.util.function.UnaryOperator;

public class GFG {
    public static void main(String args[])
    {
        UnaryOperator<Integer> xor = a -> a ^ 1;
        UnaryOperator<Integer> and = a -> a & 1;
        Function<Integer, Integer> compose = xor.compose(and);
        System.out.println(compose.apply(231));
    }
}
Output: 
0
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