Java AtomicLongArray getAndAccumulate()用法及代码示例

Java.util.concurrent.atomic.AtomicLongArray.getAndAccumulate()是Java中的一种内置方法，在将给定函数应用于当前值和给定值后，原子地更新AtomicLongArray的任何索引的值，并返回先前的值。此方法接受要执行操作的AtomicLongArray的索引，执行操作所用的值以及累加器函数作为参数。应用该函数时，将index处的当前值作为其第一个参数，并将给定的update作为第二个参数。累加器函数应无副作用，因为当尝试更新由于线程间争用而失败时，可以重新应用累加器函数。函数getAndAccumulate()与accumulateAndGet()类似，但前一个函数在更新前返回值，而后者在更新后返回值。

用法:

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

参数：该函数接受三个参数：

i–要进行更新的索引。
x–以i处的值进行运算的值
accumulatorFunction–两个参数的无副作用函数。

返回值：该函数返回long类型的更新之前的值。
以下示例程序旨在说明上述方法：
示例1:

// 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]

示例2:

// 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/util/concurrent/atomic/AtomicLongArray.html#getAndAccumulate-int-long-java.util.function.LongBinaryOperator-

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注：本文由纯净天空筛选整理自rupesh_rao大神的英文原创作品 AtomicLongArray getAndAccumulate() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。