Java 8 UnaryOperator Examples

By mkyong | Updated: March 2, 2020

Viewed: 11,439 (+102 pv/w)

Tags: function functional interface higher order function java 8 unaryoperator

In Java 8, UnaryOperator is a functional interface and it extends Function.

The UnaryOperator takes one argument, and returns a result of the same type of its arguments.

@FunctionalInterface
public interface UnaryOperator<T> extends Function<T, T> {
}

The Function takes one argument of any type and returns a result of any type.

@FunctionalInterface
public interface Function<T, R> {
    R apply(T t);
}

Further Read Java 8 Function Examples

1. UnaryOperator

1.1 In this example, the Function<Integer, Integer> which accepts and returns the same type, can be replaced with UnaryOperator<Integer>.

package com.mkyong;

import java.util.function.Function;
import java.util.function.UnaryOperator;

public class Java8UnaryOperator1 {

    public static void main(String[] args) {

        Function<Integer, Integer> func = x -> x * 2;

        Integer result = func.apply(2);

        System.out.println(result);         // 4

        UnaryOperator<Integer> func2 = x -> x * 2;

        Integer result2 = func2.apply(2);

        System.out.println(result2);        // 4

    }

}

Output

4
4

2. UnaryOperator as argument

package com.mkyong;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.UnaryOperator;

public class Java8UnaryOperator2 {

    public static void main(String[] args) {

        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        List<Integer> result = math(list, x -> x * 2);

        System.out.println(result); // [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

    }

    public static <T> List<T> math(List<T> list, UnaryOperator<T> uo) {
        List<T> result = new ArrayList<>();
        for (T t : list) {
            result.add(uo.apply(t));
        }
        return result;
    }

}

Output

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

3. Chain UnaryOperator

package com.mkyong;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.UnaryOperator;

public class Java8UnaryOperator3 {

    public static void main(String[] args) {

        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        List<Integer> result = math(list,
                x -> x * 2,
                x -> x + 1);

        System.out.println(result); // [3, 5, 7, 9, 11, 13, 15, 17, 19, 21]

    }

    public static <T> List<T> math(List<T> list,
                                   UnaryOperator<T> uo, UnaryOperator<T> uo2) {
        List<T> result = new ArrayList<>();
        for (T t : list) {
            result.add(uo.andThen(uo2).apply(t));
        }
        return result;
    }

}

Output

[3, 5, 7, 9, 11, 13, 15, 17, 19, 21]

References

• UnaryOperator JavaDoc
• Function JavaDoc
• Java 8 Function Examples
• Java 8 Tutorials