Java AtomicLongArray compareAndSet()方法及示例

Java.util.concurrent.atomic.AtomicLongArray.compareAndSet() 是java中的一个内置方法，如果当前值与预期值相等，则将某个位置上的元素原子化地设置为给定的更新值。该方法将索引值、预期值和更新值作为参数，并返回一个布尔值，说明该值是否已经被更新。

语法

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

参数： 该函数接受三个参数。

• i : 将要进行操作的索引。
• expect : 要检查是否等于当前值的预期值。
• update : 要更新的值。要更新的值。

返回值 ：该函数返回一个布尔值，说明该值是否已经被更新。如果成功则返回true，否则返回false，表明当前值不等于预期值。

以下程序说明了上述方法：

程序1 :

// Java program that demonstrates
// the compareAndSet() function
  
import java.util.concurrent.atomic.AtomicLongArray;
  
public class GFG {
    public static void main(String args[])
    {
        // Initializing an array
        long a[] = { 1, 2, 3, 4, 5 };
  
        // Initializing an AtomicLongArray with array a
        AtomicLongArray arr = new AtomicLongArray(a);
  
        // Displaying the AtomicLongArray
        System.out.println("The array : " + arr);
  
        // Index where operation is performed
        int idx = 3;
  
        // Value to expect at idx
        long expect = 4;
  
        // Value to update if current value
        // is equal to expected value
        long update = 40;
  
        // Updating the value at idx
        // applying compareAndSet
        arr.compareAndSet(idx, expect, update);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after update : "
                           + arr);
    }
}

输出。

The array : [1, 2, 3, 4, 5]
The array after update : [1, 2, 3, 40, 5]

程序2

// Java program that demonstrates
// the compareAndSet() function
  
import java.util.concurrent.atomic.AtomicLongArray;
  
public class GFG {
    public static void main(String args[])
    {
        // Initializing an array
        long a[] = { 1, 2, 3, 4, 5 };
  
        // Initializing an AtomicLongArray with array a
        AtomicLongArray arr = new AtomicLongArray(a);
  
        // Displaying the AtomicLongArray
        System.out.println("The array : " + arr);
  
        // Index where operation is performed
        int idx = 3;
  
        // Value to expect at idx
        long expect = 40;
  
        // Value to update if current value
        // is equal to expected value
        long update = 4;
  
        // Updating the value at
        // idx applying compareAndSet
        arr.compareAndSet(idx, expect, update);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after update : "
                           + arr);
    }
}

输出。

The array : [1, 2, 3, 4, 5]
The array after update : [1, 2, 3, 4, 5]

参考资料:
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicLongArray.html#compareAndSet-int-long-long-