Java Concurrency - AtomicIntegerArray Class


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A java.util.concurrent.atomic.AtomicIntegerArray class provides operations on underlying int array that can be read and written atomically, and also contains advanced atomic operations. AtomicIntegerArray supports atomic operations on underlying int array variable. It have get and set methods that work like reads and writes on volatile variables. That is, a set has a happens-before relationship with any subsequent get on the same variable. The atomic compareAndSet method also has these memory consistency features.

AtomicIntegerArray Methods

Following is the list of important methods available in the AtomicIntegerArray class.

Sr.No. Method & Description
1

public int addAndGet(int i, int delta)

Atomically adds the given value to the element at index i.

2

public boolean compareAndSet(int i, int expect, int update)

Atomically sets the element at position i to the given updated value if the current value == the expected value.

3

public int decrementAndGet(int i)

Atomically decrements by one the element at index i.

4

public int get(int i)

Gets the current value at position i.

5

public int getAndAdd(int i, int delta)

Atomically adds the given value to the element at index i.

6

public int getAndDecrement(int i)

Atomically decrements by one the element at index i.

7

public int getAndIncrement(int i)

Atomically increments by one the element at index i.

8

public int getAndSet(int i, int newValue)

Atomically sets the element at position i to the given value and returns the old value.

9

public int incrementAndGet(int i)

Atomically increments by one the element at index i.

10

public void lazySet(int i, int newValue)

Eventually sets the element at position i to the given value.

11

public int length()

Returns the length of the array.

12

public void set(int i, int newValue)

Sets the element at position i to the given value.

13

public String toString()

Returns the String representation of the current values of array.

14

public boolean weakCompareAndSet(int i, int expect, int update)

Atomically sets the element at position i to the given updated value if the current value == the expected value.

Example

The following TestThread program shows usage of AtomicIntegerArray variable in thread based environment.

Live Demo
import java.util.concurrent.atomic.AtomicIntegerArray;

public class TestThread {
   private static AtomicIntegerArray atomicIntegerArray = new AtomicIntegerArray(10);

   public static void main(final String[] arguments) throws InterruptedException {
      
      for (int i = 0; i<atomicIntegerArray.length(); i++) {
         atomicIntegerArray.set(i, 1);
      }

      Thread t1 = new Thread(new Increment());
      Thread t2 = new Thread(new Compare());
      t1.start();
      t2.start();

      t1.join();
      t2.join();

      System.out.println("Values: ");

      for (int i = 0; i<atomicIntegerArray.length(); i++) {
         System.out.print(atomicIntegerArray.get(i) + " ");
      }
   }

   static class Increment implements Runnable {

      public void run() {

         for(int i = 0; i<atomicIntegerArray.length(); i++) {
            int add = atomicIntegerArray.incrementAndGet(i);
            System.out.println("Thread " + Thread.currentThread().getId() 
               + ", index " +i + ", value: "+ add);
         }
      }
   }

   static class Compare implements Runnable {

      public void run() {

         for(int i = 0; i<atomicIntegerArray.length(); i++) {
            boolean swapped = atomicIntegerArray.compareAndSet(i, 2, 3);
            
            if(swapped) {
               System.out.println("Thread " + Thread.currentThread().getId()
                  + ", index " +i + ", value: 3");
            }
         }
      }
   }
}

This will produce the following result.

Output

Thread 10, index 0, value: 2
Thread 10, index 1, value: 2
Thread 10, index 2, value: 2
Thread 11, index 0, value: 3
Thread 10, index 3, value: 2
Thread 11, index 1, value: 3
Thread 11, index 2, value: 3
Thread 10, index 4, value: 2
Thread 11, index 3, value: 3
Thread 10, index 5, value: 2
Thread 10, index 6, value: 2
Thread 11, index 4, value: 3
Thread 10, index 7, value: 2
Thread 11, index 5, value: 3
Thread 10, index 8, value: 2
Thread 11, index 6, value: 3
Thread 10, index 9, value: 2
Thread 11, index 7, value: 3
Thread 11, index 8, value: 3
Thread 11, index 9, value: 3
Values:
3 3 3 3 3 3 3 3 3 3


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