Java AtomicReference compareAndSet()用法及代碼示例

如果AtomicReference對象的當前值等於期望值，則使用AtomicReference類的compareAndSet()方法以原子方式將newValue的值設置為AtomicReference對象，如果操作成功，則返回true，否則返回false。此方法使用設置的內存語義更新值，就像將該變量聲明為volatile一樣。

用法:

public final V compareAndSet(V expectedValue,
                             V newValue)

參數：該方法接受ExpectedValue(期望值)和newValue(新值)來設置新值。

返回值：此方法返回見證值，如果成功，它將與期望值相同。

以下示例程序旨在說明compareAndSet()方法：
程序1:

// Java program to demonstrate 
// AtomicReference.compareAndSet() method 
  
import java.util.concurrent.atomic.AtomicReference; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
  
        // create an atomic reference object. 
        AtomicReference<Long> ref 
            = new AtomicReference<Long>(); 
  
        // set some value 
        ref.set(987654321L); 
  
        // apply compareAndSet() 
        boolean response 
            = ref.compareAndSet(1234L, 
                                999999L); 
  
        // print value 
        System.out.println(" Value is set = "
                           + response); 
    } 
}

輸出：

Value is set = false

程序2:

// Java program to demonstrate 
// AtomicReference.compareAndSet() method 
  
import java.util.concurrent.atomic.AtomicReference; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
  
        // create an atomic reference object. 
        AtomicReference<String> ref 
            = new AtomicReference<String>(); 
  
        // set some value 
        ref.set("Geeks For Geeks"); 
  
        // apply compareAndSet() 
        boolean response 
            = ref.compareAndSet( 
                "Geeks For Geeks", 
                "GFG"); 
  
        // print value 
        System.out.println(" Value is set = "
                           + response); 
    } 
}

輸出：

Value is set = true

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

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