Java中的 AtomicReference compareAndExchangeAcquire() 方法及示例

AtomicReference类的compareAndExchangeAcquire()方法用于原子地将值设置为 newValue 到 AtomicReference 对象，如果称为见证值的 AtomicReference 对象的当前值等于预期值并返回见证值。此方法使用与 memory_order_acquire 排序兼容的内存排序效果交换值。

句法：

public final V compareAndExchangeAcquire(V expectedValue,
                                         V newValue)

参数：此方法接受期望值和newValue ，这是要设置的新值。

返回值：该方法返回见证值，如果成功则与预期值相同。

下面的程序说明了 compareAndExchangeAcquire() 方法：
方案一：

// Java program to demonstrate
// AtomicReference.compareAndExchangeAcquire() method
  
import java.util.concurrent.atomic.AtomicReference;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an atomic reference object
        // which stores Integer.
        AtomicReference ref
            = new AtomicReference();
  
        // set some value
        ref.set(0.199);
  
        // apply compareAndExchangeAcquire()
        double oldValue
            = ref.compareAndExchangeAcquire(
                0.199,
                999.999);
  
        // print value
        System.out.println("Witness Value = "
                           + oldValue);
    }
}

输出：

方案二：

// Java program to demonstrate
// AtomicReference.compareAndExchangeAcquire() method
  
import java.util.concurrent.atomic.AtomicReference;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an atomic reference object.
        AtomicReference ref
            = new AtomicReference();
  
        // set some value
        ref.set("Weeks");
  
        // apply compareAndExchangeAcquire()
        String oldValue
            = ref.compareAndExchangeAcquire(
                "Weeks",
                "Days");
  
        // print value
        System.out.println("Witness Value = "
                           + oldValue);
    }
}

输出：

参考： https: Java/util/concurrent/atomic/AtomicReference.html#compareAndExchangeAcquire(V, V)