Java AtomicBoolean compareAndSet()用法及代碼示例

java.util.concurrent.atomic.AtomicBoolean.compareAndSet()是java中的一種內置方法，如果當前值等於參數給定的期望值，則將值設置為參數中的傳遞值。該函數返回一個布爾值，該布爾值使我們了解更新是否完成。

用法:

public final boolean compareAndSet(boolean expect, boolean val)

參數：該函數接受兩個強製性參數，如下所述：

expect:它指定原子對象應為的值。
val:如果原子布爾等於期望值，它指定要更新的值。

返回值：該函數返回一個布爾值，成功則返回true，否則返回false。

以下示例程序旨在說明上述函數：

示例1:

// Java Program to demonstrates 
// the compareAndSet() function 
  
import java.util.concurrent.atomic.AtomicBoolean; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
  
        // Initially value as false 
        AtomicBoolean val = new AtomicBoolean(false); 
  
        // Prints the updated value 
        System.out.println("Previous value: "
                           + val); 
  
        // Checks if previous value was false 
        // and then updates it 
        boolean res = val.compareAndSet(false, true); 
  
        // Checks if the value was updated. 
        if (res) 
            System.out.println("The value was"
                               + " updated and it is "
                               + val); 
        else
            System.out.println("The value was "
                               + "not updated"); 
    } 
}

輸出：

Previous value: false
The value was updated and it is true

示例2:

// Java Program to demonstrates 
// the compareAndSet() function 
  
import java.util.concurrent.atomic.AtomicBoolean; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
  
        // Initially value as true 
        AtomicBoolean val = new AtomicBoolean(true); 
  
        // Prints the updated value 
        System.out.println("Previous value: "
                           + val); 
  
        // Checks if previous value was true 
        // and then updates it 
        boolean res = val.compareAndSet(true, false); 
  
        // Checks if the value was updated. 
        if (res) 
            System.out.println("The value was"
                               + " updated and it is "
                               + val); 
        else
            System.out.println("The value was "
                               + "not updated"); 
    } 
}

輸出：

Previous value: true
The value was updated and it is false

參考： https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicBoolean.html#compareAndSet(boolean, %20boolean)

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