Java AtomicReferenceArray compareAndSet()用法及代碼示例

如果AtomicReferenceArray對象的索引i處的當前值等於期望值，則使用AtomicReferenceArray類的compareAndSet()方法原子地將AtomicReferenceArray的索引i的值設置為newValue。如果更新成功，則此方法將返回true。

用法:

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

參數：此方法接受：

i這是執行操作的AtomicReferenceArray的索引，
expectedValue 這是期望值，
newValue 這是要設置的新值。

返回值：如果成功，則此方法返回true；如果返回false，則表明實際值不等於期望值。

以下示例程序旨在說明compareAndSet()方法：

程序1:

// Java program to demonstrate 
// compareAndSet() 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 compareAndSet() 
        boolean op1 
            = ref.compareAndSet(0, 5434, 8913); 
        boolean op2 
            = ref.compareAndSet(1, 3236, 6543); 
  
        // print 
        System.out.println("Operation at index 0:"
                           + op1); 
        System.out.println("Operation at index 0:"
                           + op2); 
    } 
}

輸出：

Operation at index 0:false
Operation at index 0:false

程序2:

// Java program to demonstrate 
// compareAndSet() 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 compareAndSet() 
        boolean op1 
            = ref.compareAndSet( 
                0, "GFG", 
                "GEEKS FOR GEEKS"); 
        boolean op2 
            = ref.compareAndSet( 
                1, "JS", 
                "JAVA SCRIPT"); 
  
        // print 
        System.out.println("Operation at index 0:"
                           + op1); 
        System.out.println("New value at index 0:"
                           + ref.get(0)); 
        System.out.println("Operation at index 1:"
                           + op2); 
        System.out.println("New value at index 1:"
                           + ref.get(1)); 
    } 
}

輸出：

Operation at index 0:true
New value at index 0:GEEKS FOR GEEKS
Operation at index 1:true
New value at index 1:JAVA SCRIPT

參考文獻： https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/atomic/AtomicReferenceArray.html#compareAndSet(int, E, E)

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