java - 为什么for循环可以初始化Java中按值传递的变量

码：

 import java.util.Arrays;

class Heapify {
  int[] array;

  Heapify (int[] array){
   this.array = array;
  }


  public  void heap (int[] aArray){
    int left = 0;
    int right  = aArray.length - 1;
    int n = aArray.length;
    int numOfSwap  = 0;
    heapify1(aArray, left, right, numOfSwap );
  }


  public void heapify1 (int[] aArray, int left, int right, int numOfSwap) {
    //from last one that have a child
    for (int i = (right - 1)/2; i > left - 1;  --i){
      System.out.println("in heapify for loop with i =  " + i + "    number of swap: " + numOfSwap);
      if (aArray[2*i + 2] > aArray[i]) {//if right child is bigger than parent
        System.out.println("in heapify for loop and if #1: " + numOfSwap);
        swap(aArray, i, 2*i + 2, right, numOfSwap);
      }
      else if (aArray[2*i + 1] > aArray[i]){
        System.out.println("in heapify for loop and else if #2: " + numOfSwap);
        swap(aArray, i, 2*i + 1, right, numOfSwap);
      }
    }
  }


  public int swap (int[] aArray, int parent, int child, int right, int numOfSwap ){
    System.out.println("in swap before: " + numOfSwap );
    int temp = aArray[parent];
    aArray[parent] = aArray[child];
    aArray[child] = temp;
    numOfSwap  = numOfSwap  + 1;
    System.out.println("inswap after: " + numOfSwap );
    heapify1 (aArray, parent, right, numOfSwap );
    return numOfSwap;
  }


  public static void main(String args[]) {
    int[] array1 = new int[] {21,15,25,3,5,12,7,45,19,2,9};

    Heapify hs = new Heapify(array1);
    hs.heap(array1);
  }
}

结果打印值为：

in heapify: 0
in heapify for loop with i = 4    number of swap: 0
in heapify for loop and if #1: 0
in swap before: 0
inswap after: 1
in heapify: 1
in heapify for loop with i = 4    number of swap: 1
in heapify for loop with i = 3    number of swap: 0
in heapify for loop and if #1: 0
in swap before: 0
inswap after: 1
in heapify: 1
in heapify for loop with i = 4    number of swap: 1
in heapify for loop with i = 3    number of swap: 1
in heapify for loop and else if #2: 1
in swap before: 1
inswap after: 2
in heapify: 2
in heapify for loop with i = 4    number of swap: 2
in heapify for loop with i = 3    number of swap: 2
in heapify for loop with i = 2    number of swap: 0
in heapify for loop with i = 1    number of swap: 0
in heapify for loop and else if #2: 0

我不明白为什么swap将numOfSwap = 1传递给heapify1，但是在for循环中，第二次迭代时，numOfSwap被值0覆盖。同样在后一种情况下，为什么这样的行为覆盖发生在第三次迭代？

我知道这可能是“按引用传递”或“按值传递”的问题，但真正令我困惑的一件事是numOfSwap在交换中已从0更新为1，交换再次调用heapify1成功将numOfSwap = 1传递给heapify1。但是，为什么迭代后numOfSwap在for循环中被初始化？

最佳答案

heapify1方法有两种不同的上下文。

一种是在heapify1(aArray, left, right, numOfSwap );方法中调用heap时。在这种情况下，numOfSwap为0，并保持为0。在这种情况下，执行for循环。它可能看起来像“ numOfSwap在迭代后在for循环中被初始化了吗？”，但这不是事实。该值从不修改，并保持0。

另一个上下文是在heapify1 (aArray, parent, right, numOfSwap );方法中调用swap时，因此可以说“ swap再次调用heapify1，将numOfSwap = 1成功传递给heapify1”。但是这些传递的值仅在此上下文中使用，并且与提到的第一个上下文无关，并且不会修改numOfSwap的值为0。