Java中的 AtomicLong compareAndSet() 方法及示例

Java.util.concurrent.atomic.AtomicLong.compareAndSet()是Java中的一个内置方法，如果当前值等于参数中传递的预期值，则该方法将值设置为参数中传递的值。该函数返回一个布尔值，它让我们知道更新是否完成。

句法：

public final boolean compareAndSet(long expect,
                                       long val)

参数：该函数接受两个强制性参数，如下所述：

• 期望：指定原子对象应该是的值。
• val：如果原子整数等于expect，则指定要更新的值。

返回值：函数返回一个布尔值，成功则返回true，否则返回false。

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.AtomicLong;
  
public class GFG {
    public static void main(String args[])
    {
  
        // Initially value as 0
        AtomicLong val = new AtomicLong(0);
  
        // Prints the updated value
        System.out.println("Previous value: "
                           + val);
  
        // Checks if previous value was 0
        // and then updates it
        boolean res = val.compareAndSet(0, 6);
  
        // Checks if the value was updated.
        if (res)
            System.out.println("The value was "
                               + "updated and it is "
                               + val);
        else
            System.out.println("The value was "
                               + "not updated");
    }
}

输出：

Previous value: 0
The value was updated and it is 6

方案二：

// Java program that demonstrates
// the compareAndSet() function
  
import java.util.concurrent.atomic.AtomicLong;
  
public class GFG {
    public static void main(String args[])
    {
  
        // Initially value as 0
        AtomicLong val = new AtomicLong(0);
  
        // Prints the updated value
        System.out.println("Previous value: "
                           + val);
  
        // Checks if previous value was 0
        // and then updates it
        boolean res = val.compareAndSet(10, 6);
  
        // Checks if the value was updated.
        if (res)
            System.out.println("The value was "
                               + "updated and it is "
                               + val);
        else
            System.out.println("The value was "
                               + "not updated");
    }
}

输出：

Previous value: 0
The value was not updated

参考： https: Java/util/concurrent/atomic/AtomicLong.html#compareAndSet–