Java中的 AtomicLongArray compareAndSet() 方法及示例

Java.util.concurrent.atomic.AtomicLongArray.compareAndSet()是Java中的一个内置方法，如果当前值等于预期值，它会自动将某个位置的元素设置为给定的更新值。该方法将索引值、期望值和更新值作为参数，并返回一个布尔值，说明该值是否已更新。

句法：

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

参数：该函数接受三个参数：

i ：要进行操作的索引。

expect ：检查它是否等于当前值的期望值。

update ：要更新的值。

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

下面的程序说明了上述方法：
方案一：

// 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]

方案二：

// 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：
https://docs.oracle.com/javase/8/docs/api/java Java