Java AtomicReference weakCompareAndSet()用法及代碼示例

如果當前值等於作為參數傳遞的ExpectedValue，則使用AtomicReference類的weakCompareAndSet()方法為AtomicReference原子地將值設置為newValue。此方法使用讀取的存儲器語義來更新值，就像將變量聲明為變量的易失性類型一樣。如果成功將AtomicReference設置為新值，則此方法返回true。

用法:

public final boolean weakCompareAndSet(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：如果成功，則此方法返回true。

以下示例程序旨在說明weakCompareAndSet()方法：
程序1:

// Java program to demonstrate 
// AtomicReference.weakCompareAndSet() 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<Integer> ref 
            = new AtomicReference<Integer>(); 
  
        // set some value 
        ref.set(999); 
  
        // apply weakCompareAndSet() 
        boolean result 
            = ref.weakCompareAndSet(999, 
                                    999999); 
  
        // print value 
        System.out.println("Setting new value"
                           + " is successful = "
                           + result); 
        System.out.println("New Value = "
                           + ref.get()); 
    } 
}

輸出：

Setting new value is successful = false
New Value = 999

程序2:

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

輸出：

Value  = GFG

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

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