Java中的 AtomicReferenceArray compareAndExchange() 方法及示例

AtomicReferenceArray类的compareAndExchange()方法用于将 AtomicReferenceArray 的索引 i 的值自动设置为 newValue，如果被称为见证值的 AtomicReferenceArray 对象的索引 i 处的当前值等于预期值。此方法将返回见证值，该值与预期值相同。此方法处理具有读取的内存语义的操作，就好像变量被声明为易失性一样。

句法：

public final boolean
       compareAndExchange(
           int i, E expectedValue, E newValue)

参数：此方法接受：

• i是执行操作的 AtomicReferenceArray 的索引，
• expectedValue是期望值和
• newValue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 compareAndExchange() 方法：
方案一：

// Java program to demonstrate
// compareAndExchange() method
  
import java.util.concurrent.atomic.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // create an atomic reference object.
        AtomicReferenceArray ref
            = new AtomicReferenceArray(3);
  
        // set some value
        ref.set(0, 1234);
        ref.set(1, 4322);
  
        // apply compareAndExchange()
        int oldV1
            = ref.compareAndExchange(0, 1234, 8913);
        int oldV2
            = ref.compareAndExchange(1, 4322, 6543);
  
        // print
        System.out.println("Old value at index 0: "
                           + oldV1);
        System.out.println("Old value at index 1: "
                           + oldV2);
    }
}

输出：

方案二：

// Java program to demonstrate
// compareAndExchange() method
  
import java.util.concurrent.atomic.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // create an atomic reference object.
        AtomicReferenceArray ref
            = new AtomicReferenceArray(3);
  
        // set some value
        ref.set(0, "GFG");
        ref.set(1, "JS");
  
        // apply compareAndExchange()
        String oldV1
            = ref.compareAndExchange(
                0, "GFG",
                "GEEKS FOR GEEKS");
        String oldV2
            = ref.compareAndExchange(
                1, "JS",
                "JAVA SCRIPT");
  
        // print
        System.out.println("Old value at index 0: "
                           + oldV1);
        System.out.println("New value at index 0: "
                           + ref.get(0));
        System.out.println("Old value at index 1: "
                           + oldV2);
        System.out.println("New value at index 1: "
                           + ref.get(1));
    }
}

输出：

参考： https: Java/util/concurrent/atomic/AtomicReferenceArray.html#compareAndExchange(int, E, E)