Java AtomicLongArray getAndDecrement()方法及示例

Java.util.concurrent.atomic.AtomicLongArray.getAndDecrement() 是Java中的一个内置方法，它可以将给定索引的值原子化地递减1。该方法获取AtomicLongArray的索引值，并返回该索引处存在的值，然后递减该索引处的值。 getAndDecrement() 函数与 decrementAndGet() 函数类似，但后一个函数返回递减后的值，而前一个则返回递减前的值。

语法

public final long getAndDecrement(int i)

参数： 该函数接受一个参数i，它是执行递减1操作的索引。

返回值： 该函数返回在索引处进行递减操作之前的值，该索引的单位是long。

以下程序说明了上述方法：

程序1 :

// Java program that demonstrates
// the getAndDecrement() function
  
import java.util.concurrent.atomic.AtomicLongArray;
  
public class GFG {
    public static void main(String args[])
    {
        // Initializing an array
        long a[] = { 1, 2, 3, 4, 5 };
  
        // Initializing an AtomicLongArray with array a
        AtomicLongArray arr = new AtomicLongArray(a);
  
        // Displaying the AtomicLongArray
        System.out.println("The array : " + arr);
  
        // Index where operation is performed
        int idx = 3;
  
        // Decrementing the value at
        // idx applying getAndDecrement
        // and storing previous value
        long prev = arr.getAndDecrement(idx);
  
        // The previous value at idx
        System.out.println("Value at index " + idx
                           + " before decrement is "
                           + prev);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after decrement : "
                           + arr);
    }
}

输出。

The array : [1, 2, 3, 4, 5]
Value at index 3 before decrement is 4
The array after decrement : [1, 2, 3, 3, 5]

程序2

// Java program that demonstrates
// the getAndDecrement() function
  
import java.util.concurrent.atomic.AtomicLongArray;
  
public class GFG {
    public static void main(String args[])
    {
        // Initializing an array
        long a[] = { 10, 20, 30, 40, 50 };
  
        // Initializing an AtomicLongArray with array a
        AtomicLongArray arr = new AtomicLongArray(a);
  
        // Displaying the AtomicLongArray
        System.out.println("The array : " + arr);
  
        // Index where operation is performed
        int idx = 0;
  
        // Decrementing the value at
        // idx applying getAndDecrement
        // and storing previous value
        long prev = arr.getAndDecrement(idx);
  
        // The previous value at idx
        System.out.println("Value at index " + idx
                           + " before decrement is "
                           + prev);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after decrement : "
                           + arr);
    }
}

输出。

The array : [10, 20, 30, 40, 50]
Value at index 0 before decrement is 10
The array after decrement : [9, 20, 30, 40, 50]

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicLongArray.html#getAndDecrement-int-