Java AtomicLongArray getAndAccumulate()用法及代碼示例

Java.util.concurrent.atomic.AtomicLongArray.getAndAccumulate()是Java中的一種內置方法，在將給定函數應用於當前值和給定值後，原子地更新AtomicLongArray的任何索引的值，並返回先前的值。此方法接受要執行操作的AtomicLongArray的索引，執行操作所用的值以及累加器函數作為參數。應用該函數時，將index處的當前值作為其第一個參數，並將給定的update作為第二個參數。累加器函數應無副作用，因為當嘗試更新由於線程間爭用而失敗時，可以重新應用累加器函數。函數getAndAccumulate()與accumulateAndGet()類似，但前一個函數在更新前返回值，而後者在更新後返回值。

用法:

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

參數：該函數接受三個參數：

i–要進行更新的索引。
x–以i處的值進行運算的值
accumulatorFunction–兩個參數的無副作用函數。

返回值：該函數返回long類型的更新之前的值。
以下示例程序旨在說明上述方法：
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); 
    } 
}

輸出：

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); 
    } 
}

輸出：

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

參考：
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：本文由純淨天空篩選整理自rupesh_rao大神的英文原創作品 AtomicLongArray getAndAccumulate() method in Java with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。