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Java AtomicReferenceArray compareAndExchange()用法及代码示例


如果AtomicReferenceArray对象的索引i处的当前值(称为见证值)等于期望值,则使用AtomicReferenceArray类的compareAndExchange()方法原子地将AtomicReferenceArray的索引i的值设置为newValue。此方法将返回见证值,该值将与期望值相同。此方法使用读取的内存语义来处理操作,就像将该变量声明为volatile一样。

用法:

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

参数:此方法接受:


  • i这是执行操作的AtomicReferenceArray的索引,
  • expectedValue 这是期望值,
  • newValue 这是要设置的新值。

返回值:此方法返回见证值,如果成功,它将与期望值相同。

以下示例程序旨在说明compareAndExchange()方法:
程序1:

// 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<Integer> ref 
            = new AtomicReferenceArray<Integer>(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:

程序2:

// 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<String> ref 
            = new AtomicReferenceArray<String>(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:

参考文献: https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/atomic/AtomicReferenceArray.html#compareAndExchange(int, E, E)



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