Java AtomicLong compareAndSet()方法及示例

Java.util.concurrent.atomic.AtomicLong.compareAndSet() 是java中的一个内置方法，如果当前值与参数中传递的预期值相等，则将该值设置为参数中传递的值。该函数返回一个布尔值，让我们知道是否已经完成了更新。

语法

public final boolean compareAndSet(long expect,
                                       long val)

参数： 该函数接受两个强制性参数，描述如下。

• expect： 指定原子对象应该是的值。
• val： 指定在原子整数等于期望值时要更新的值。

返回值： 该函数返回一个布尔值，成功时返回真，否则返回假。

下面的程序说明了上述方法。

程序1 :

// 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

程序2

// 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

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