Java AtomicInteger weakCompareAndSet()用法及代碼示例

java.util.concurrent.atomic.AtomicInteger.weakCompareAndSet()是Java中的一種內置方法，如果當前值等於參數給定的期望值，則將值設置為參數中的傳遞值。該函數返回一個布爾值，該布爾值使我們了解更新是否完成。

用法:

public final boolean weakCompareAndSet(int expect,
                                       int val)

參數：該函數接受兩個強製性參數，如下所述：

expect:指定原子對象應為的值。
val:如果原子整數等於期望值，則指定要更新的值。

返回值：該函數返回一個布爾值，成功則返回true，否則返回false。

以下程序演示了該函數：

示例1:

// Java program that demonstrates 
// the weakCompareAndSet() function 
  
import java.util.concurrent.atomic.AtomicInteger; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
  
        // Initially value as 0 
        AtomicInteger val 
            = new AtomicInteger(0); 
  
        // Prints the updated value 
        System.out.println("Previous value: "
                           + val); 
  
        // Checks if previous value was 0 
        // and then updates it 
        boolean res 
            = val.weakCompareAndSet(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"); 
    } 
}

輸出：

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

示例2:

// Java program that demonstrates 
// the weakCompareAndSet() function 
  
import java.util.concurrent.atomic.AtomicInteger; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
  
        // Initially value as 0 
        AtomicInteger val 
            = new AtomicInteger(0); 
  
        // Prints the updated value 
        System.out.println("Previous value: "
                           + val); 
  
        // Checks if previous value was 0 
        // and then updates it 
        boolean res 
            = val.weakCompareAndSet(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"); 
    } 
}

輸出：

Previous value: 0
The value was not updated

參考： https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicInteger.html#weakCompareAndSet–

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