Java中的 AtomicLongArray getAndAccumulate() 方法及示例

Java.util.concurrent.atomic.AtomicLongArray.getAndAccumulate()是Java中的一个内置方法，它在将给定函数应用于当前值和给定值后，用结果原子更新 AtomicLongArray 的任何索引处的值，返回前一个值.此方法接受要执行操作的 AtomicLongArray 的索引、执行操作的值和累加器函数作为参数。该函数应用索引处的当前值作为其第一个参数，并将给定的更新作为第二个参数。累加器函数应该没有副作用，因为当尝试更新由于线程之间的争用而失败时，它可能会被重新应用。 getAndAccumulate()函数与accumulateAndGet()函数类似，但前者返回更新前的值，而后者返回更新后的值。

句法：

public final long getAndAccumulate(int i, long x, LongBinaryOperator accumulatorFunction)

编程需要懂一点英语

参数：该函数接受三个参数：

i – 要进行更新的索引。

x – 使用 i 处的值进行操作的值

accumulatorFunction – 两个参数的无副作用函数。

返回值：函数返回更新前的值，在long中。
下面的程序说明了上述方法：
方案一：

// Java program that demonstrates
// the getAndAccumulate() function
  
import java.util.concurrent.atomic.AtomicLongArray;
import java.util.function.LongBinaryOperator;
  
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 update is to be made
        int idx = 4;
  
        // Value to make operation with value at idx
        long x = 5;
  
        // Declaring the accumulatorFunction
        LongBinaryOperator add = (u, v) -> u + v;
  
        // Updating the value at idx
        // applying getAndAccumulate
        long prev = arr.getAndAccumulate(idx, x, add);
  
        // The previous value at idx
        System.out.println("Value at index " + idx
                           + " before update is "
                           + prev);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after update : "
                           + arr);
    }
}

输出：

The array : [1, 2, 3, 4, 5]
Value at index 4 before update is 5
The array after update : [1, 2, 3, 4, 10]

方案二：

// Java program that demonstrates
// the getAndAccumulate() function
  
import java.util.concurrent.atomic.AtomicLongArray;
import java.util.function.LongBinaryOperator;
  
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 update is to be made
        int idx = 0;
  
        // Value to make operation with value at idx
        long x = 6;
  
        // Declaring the accumulatorFunction
        LongBinaryOperator sub = (u, v) -> u - v;
  
        // Updating the value at idx
        // applying getAndAccumulate
        long prev = arr.getAndAccumulate(idx, x, sub);
  
        // The previous value at idx
        System.out.println("Value at index " + idx
                           + " before update is "
                           + prev);
  
        // Displaying the AtomicLongArray
        System.out.println("The array after update : "
                           + arr);
    }
}

输出：

The array : [1, 2, 3, 4, 5]
Value at index 0 before update is 1
The array after update : [-5, 2, 3, 4, 5]

参考：
https://docs.oracle.com/javase/8/docs/api/java Java。函数.LongBinaryOperator-