The BinaryOperator<T> interface is a specialized functional interface introduced in Java 8 and available in the java.util.function package. It represents an operation that takes two operands of the same type and returns a result of the same type.

• Specialized form of BiFunction<T, T, T>.
• Accepts two arguments of the same type.
• Commonly used for comparison, aggregation, and reduction operations.

import java.util.function.BinaryOperator;

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

        BinaryOperator<Integer> add =
            (a, b) -> a + b;

        System.out.println(
            "Sum = " + add.apply(10, 20)
        );
    }
}

Sum = 30

Explanation: In this example, the BinaryOperator accepts two integers and returns their sum. Since the input and output types are the same (Integer), BinaryOperator is a suitable choice.

Syntax

@FunctionalInterface
public interface BinaryOperator<T>
extends BiFunction<T, T, T>

Here,

• T :Type of both input arguments and the return value.

Methods of BinaryOperator Interface

1. maxBy() Method

The maxBy() method returns a BinaryOperator that selects the greater of two elements according to the specified Comparator. Returns the maximum of two values.

• Uses a Comparator for comparison.
• Useful for finding the largest element.

Syntax:

static <T> BinaryOperator<T>
maxBy(Comparator<? super T> comparator)

• Parameters: comparator: Comparator used to compare two values.
• Return Value: Returns a BinaryOperator that returns the larger of the two operands.

import java.util.function.BinaryOperator;

public class GFG {
    public static void main(String args[])
    {
        BinaryOperator<Integer>
            op = BinaryOperator
                     .maxBy(
                         (a, b) -> (a > b) ? 1 : ((a == b) ? 0 : -1));

        System.out.println(op.apply(98, 11));
    }
}

98

Explanation: The maxBy() method compares 98 and 11 using Integer.compare(). Since 98 is greater, it is returned as the result.

2. minBy()

This method returns a BinaryOperator which returns the lesser of the two elements based on a given comparator

Syntax: 

static <T> BinaryOperator<T> 
    minBy(Comparator<? super T> comparator)

Parameters: It takes in only one parameter namely, comparator which is an object of the Comparator class.
Returns: This method returns a BinaryOperator which return the minimum of the two objects passed while calling it based on the given comparator.

import java.util.function.BinaryOperator;

public class GFG {
    public static void main(String args[])
    {
        BinaryOperator<Integer>
            op = BinaryOperator
                     .minBy(
                         (a, b) -> (a > b) ? 1 : ((a == b) ? 0 : -1));

        System.out.println(op.apply(98, 11));
    }
}

11

Explanation: The minBy() method compares 98 and 11 using Integer.compare(). Since 11 is smaller, it is returned as the result.

BinaryOperator vs BiFunction

Advantages of BinaryOperator

• Simplifies operations where all types are the same.
• Reduces boilerplate code compared to BiFunction.
• Supports lambda expressions and method references.
• Useful for finding minimum and maximum values.
• Commonly used in Stream API reduction operations.
• Improves code readability and maintainability.