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The accumulateAndGet() method of a AtomicReferenceArray class is used to atomically updates the element at index i of AtomicReferenceArray with the results of applying the given accumulatorFunction to the current and given values and returns the updated value. The accumulatorFunction should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value at index i as its first argument, and the given update as the second argument. Syntax:

public final E accumulateAndGet(int i, E x,
     BinaryOperator<E> accumulatorFunction)

Parameters: This method accepts:

i which is an index of AtomicReferenceArray to perform the operation accepts,
x which is the updated value and
accumulatorFunction which is a side-effect-free function of two arguments.

Return value: This method returns the updated value. Below programs illustrate the accumulateAndGet() method: Program 1:

Java

// Java program to demonstrate
// accumulateAndGet() method

import java.util.concurrent.atomic.*;
import java.util.function.BinaryOperator;

public class GFG {
    public static void main(String args[])
    {
        // an array
        Integer a[] = { 123, 1232, 1433, 134, 13415, 1343 };

        // AtomicReferenceArray with array
        AtomicReferenceArray<Integer> array
            = new AtomicReferenceArray<>(a);

        // Print AtomicReferenceArray
        System.out.println(
            "The AtomicReferenceArray before update\n: "
            + array);

        // Index and Value to apply accumulateAndGet
        int index = 2;
        int E = 343;

        // Declaring the accumulatorFunction
        // applying function to add value as string
        BinaryOperator add
            = (u, v)
            -> u.toString()
                   + v.toString();

        // apply accumulateAndGet()
        array.accumulateAndGet(index, E, add);

        // print AtomicReferenceArray
        System.out.println(
            "The AtomicReferenceArray "
            + "after update \n: "
            + array);
    }
}

Output:

Program 2:

Java

// Java program to demonstrate
// accumulateAndGet() method

import java.util.concurrent.atomic.*;
import java.util.function.BinaryOperator;

public class GFG {
    public static void main(String args[])
    {
        // an array
        String a[] = { "GFG", "JS" };

        // AtomicReferenceArray with array
        AtomicReferenceArray<String> arra
            = new AtomicReferenceArray<>(a);

        // Print AtomicReferenceArray
        System.out.println(
            "The AtomicReferenceArray"
            + " before update \n: "
            + array);

        // Index and Value to apply accumulateAndGet
        int index = 1;
        String E = " PYTHON";

        // Declaring the accumulatorFunction
        // applying function to add value as string
        BinaryOperator add
            = (u, v)
            -> u.toString()
                   + " and "
                   + v.toString();

        // apply accumulateAndGet()
        array.accumulateAndGet(index, E, add);

        // print AtomicReferenceArray
        System.out.println(
            "The AtomicReferenceArray"
            + " after update \n: "
            + array);
    }
}

Output:

References: https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/atomic/AtomicReferenceArray.html#accumulateAndGet(int, E, java.util.function.BinaryOperator)

AtomicReferenceArray accumulateAndGet() method in Java with Examples

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