Java LongUnaryOperator Interface

Last modified: April 16, 2025

The java.util.function.LongUnaryOperator interface represents a function that accepts a single long-valued argument and produces a long-valued result. It is a functional interface with a single abstract method applyAsLong. This specialization avoids boxing/unboxing overhead.

LongUnaryOperator is part of Java’s functional programming utilities added in Java 8. It is particularly useful when working with primitive long values in streams and other functional operations. The interface provides default methods for composition.

LongUnaryOperator Interface Overview

LongUnaryOperator contains one abstract method and several default methods. The key method applyAsLong performs the operation on the input. Other methods enable function composition and chaining.

@FunctionalInterface public interface LongUnaryOperator { long applyAsLong(long operand);

default LongUnaryOperator compose(LongUnaryOperator before);
default LongUnaryOperator andThen(LongUnaryOperator after);
static LongUnaryOperator identity();

}

The code above shows the structure of LongUnaryOperator interface. Unlike generic Function, it works specifically with primitive long values. The interface is annotated with @FunctionalInterface to indicate its nature.

Basic LongUnaryOperator Usage

The simplest way to use LongUnaryOperator is with lambda expressions. We define how to transform the input long to output long. The example squares input values.

Main.java

package com.zetcode;

import java.util.function.LongUnaryOperator;

public class Main {

public static void main(String[] args) {

    // Define a function that squares a long value
    LongUnaryOperator square = x -> x * x;
    
    // Apply the function
    System.out.println("Square of 5: " + square.applyAsLong(5));
    System.out.println("Square of 12: " + square.applyAsLong(12));
    
    // Function using arithmetic expression
    LongUnaryOperator incrementAndDouble = x -> (x + 1) * 2;
    System.out.println("Increment and double 3: " + 
        incrementAndDouble.applyAsLong(3));
}

}

This example demonstrates basic LongUnaryOperator usage with lambda expressions. The square operator multiplies input by itself. We also show a more complex operation combining increment and multiplication. Results are primitive longs.

Function Composition with andThen

The andThen method allows chaining LongUnaryOperators where the output of one becomes input to the next. This enables building complex operations from simple ones.

Main.java

package com.zetcode;

import java.util.function.LongUnaryOperator;

public class Main {

public static void main(String[] args) {

    // First function increments by 1
    LongUnaryOperator increment = x -> x + 1;
    
    // Second function multiplies by 2
    LongUnaryOperator doubler = x -> x * 2;
    
    // Compose the functions
    LongUnaryOperator incrementThenDouble = increment.andThen(doubler);
    
    System.out.println("Increment then double 5: " + 
        incrementThenDouble.applyAsLong(5));
    System.out.println("Increment then double 10: " + 
        incrementThenDouble.applyAsLong(10));
}

}

This example shows function composition with andThen. The input value first gets incremented by 1, then multiplied by 2. The order of operations is left-to-right in the chain. No boxing occurs between operations.

Function Composition with compose

The compose method is similar to andThen but executes functions in reverse order. The parameter function runs first, then the original function.

Main.java

package com.zetcode;

import java.util.function.LongUnaryOperator;

public class Main {

public static void main(String[] args) {

    // Function to square a number
    LongUnaryOperator square = x -> x * x;
    
    // Function to subtract 5
    LongUnaryOperator subtractFive = x -> x - 5;
    
    // Compose in different orders
    LongUnaryOperator subtractThenSquare = square.compose(subtractFive);
    LongUnaryOperator squareThenSubtract = square.andThen(subtractFive);
    
    System.out.println("Subtract 5 then square 8: " + 
        subtractThenSquare.applyAsLong(8));
    System.out.println("Square then subtract 5 from 8: " + 
        squareThenSubtract.applyAsLong(8));
}

}

This example demonstrates the difference between compose and andThen. With compose, subtraction happens before squaring. With andThen, squaring happens before subtraction. The results show different values.

Using LongUnaryOperator with Streams

LongUnaryOperator is commonly used with LongStream for primitive long transformations. The map operation accepts a LongUnaryOperator to transform stream elements. This avoids boxing overhead in numeric operations.

Main.java

package com.zetcode;

import java.util.stream.LongStream;

public class Main {

public static void main(String[] args) {

    // Define transformation operations
    LongUnaryOperator square = x -> x * x;
    LongUnaryOperator increment = x -> x + 1;
    
    // Apply operations in stream pipeline
    LongStream.rangeClosed(1, 5)
        .map(square)
        .map(increment)
        .forEach(System.out::println);
        
    // Combined operation
    LongUnaryOperator combined = square.andThen(increment);
    System.out.println("Combined result for 3: " + 
        combined.applyAsLong(3));
}

}

This example shows LongUnaryOperator usage in LongStream. We define square and increment operations and apply them to a range of numbers. The combined operator shows how to chain operations. All operations work with primitive longs.

LongUnaryOperator Identity

The LongUnaryOperator.identity method returns a function that always returns its input argument unchanged. It’s useful as a default operation or placeholder in stream processing.

Main.java

package com.zetcode;

import java.util.function.LongUnaryOperator;

public class Main {

public static void main(String[] args) {

    // Identity function
    LongUnaryOperator identity = LongUnaryOperator.identity();
    
    System.out.println("Identity applied to 5: " + 
        identity.applyAsLong(5));
    System.out.println("Identity applied to 100: " + 
        identity.applyAsLong(100));
        
    // Using identity in stream filter
    LongStream.of(10, 20, 30)
        .map(LongUnaryOperator.identity())
        .forEach(System.out::println);
}

}

This example demonstrates LongUnaryOperator.identity. The identity function returns its input unchanged. In streams, it can serve as a no-op transformation when needed for API consistency. Results are identical to inputs.

Practical Application: Number Formatting

LongUnaryOperator can be used in practical scenarios like number formatting or data transformation pipelines. This example shows a currency conversion operation chain.

Main.java

package com.zetcode;

import java.util.function.LongUnaryOperator;

public class Main {

public static void main(String[] args) {

    // Conversion rates (simplified)
    long usdToEurRate = 85; // 100 USD = 85 EUR
    long eurToGbpRate = 90; // 100 EUR = 90 GBP
    
    // Create conversion operators
    LongUnaryOperator usdToEur = usd -> usd * usdToEurRate / 100;
    LongUnaryOperator eurToGbp = eur -> eur * eurToGbpRate / 100;
    
    // Combined conversion
    LongUnaryOperator usdToGbp = usdToEur.andThen(eurToGbp);
    
    long amountInUsd = 20000; // $200.00 in cents
    System.out.println("$200 in GBP: £" + 
        usdToGbp.applyAsLong(amountInUsd) / 100.0);
        
    // Formatting operator
    LongUnaryOperator roundToNearest100 = x -> (x + 50) / 100 * 100;
    System.out.println("Rounded 1234: " + 
        roundToNearest100.applyAsLong(1234));
}

}

This example shows practical LongUnaryOperator usage. We create currency conversion operators and chain them together. The rounding operator demonstrates another common numeric operation. All calculations use primitive longs.

Source

Java LongUnaryOperator Interface Documentation

In this article, we’ve covered the essential methods and features of the Java LongUnaryOperator interface. Understanding these concepts is crucial for efficient numeric processing in modern Java applications.

Author

My name is Jan Bodnar, and I am a dedicated programmer with many years of experience in the field. I began writing programming articles in 2007 and have since authored over 1,400 articles and eight e-books. With more than eight years of teaching experience, I am committed to sharing my knowledge and helping others master programming concepts.

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