为什么这不为每个循环工作？ [英] Why doesn't this for-each loop work?

问题描述

在这段代码中，为什么我的数组没有初始化？是不是每个循环都没有这样做，或者我只是没有正确使用它？

  int [] array = new int [5]; 
 
 //初始化数组 - >>不行！数组仍然充满了0的
（int i：array）
 i = 24; 
  

解决方案

for-each循环不适用于这种情况。你不能使用for-each循环来初始化一个数组。你的代码：

  int [] array = new int [5]; 
 for（int i：array）{
 i = 24; 
 
 $ / code $ / pre 
 
 
会翻译成以下内容：
 
 
  int [] array = new int [5]; 
 for（int j = 0; j  int i = array [j]; 
 i = 24; 
 
 
 
 $ b如果这是一个对象数组，它仍然会失败。基本上，for-each将集合或数组中的每个条目依次赋值给您提供的变量，然后您可以使用该变量。该变量不等于数组引用。它只是一个变量。
 
 
 
 For-each不能用于初始化任何数组或集合，因为它循环了当前的内容数组或集合，每次给你一个值。 for-each中的变量不是 代表数组或集合引用的代理。编译器不会用替换 i （来自 int i ）如果你有一个Date的数组，例如，试试这个，代码：
 
 
 
 
  Date [] array = new Date [5]; 
 for（Date d：array）{
 d = new Date（）; 
 
 $ / code $ / pre 
 
 
会被翻译成类似这样的内容：
  Date [] array = new Date [5]; 
 for（int i = 0; i< array.length; i ++）{
 Date d = array [i]; 
 d = new Date（）; 
 
 
 
 
 
 $ b 
如你所见，不会初始化数组。注：我将上面的代码编译成 .class 文件，然后使用 jad 进行反编译。这个过程为我提供了以下代码，由Sun Java编译器（1.6）从上面的代码生成： 
 
 
  int array [] = new int [5]; 
 int ai []; 
 int k =（ai = array）.length; 
 for（int j = 0; j  {
 int i = ai [j]; 
 i = 5; 
} 
  
 
In this code, why isn't my array initialised as I want it to? Is the for-each loop not designed to do that, or am I just not using it correctly?
    int[] array = new int[5];

    //initialise array -> Doesn't work! Array still full of 0's
    for(int i : array)
        i = 24;

解决方案
The for-each loop will not work for this case.  You cannot use a for-each loop to initialize an array.  Your code:
int[] array = new int[5];
for (int i : array) {
    i = 24;
}
will translate to something like the following:
int[] array = new int[5];
for (int j = 0; j < array.length; j++) {
    int i = array[j];
    i = 24;
}
If this were an array of objects, it would still fail.  Basically, for-each assigns each entry in the collection or array, in turn, to the variable you provide, which you can then work with.  The variable is not equivalent to an array reference.  It is just a variable.


For-each cannot be used to initialize any array or Collection, because it loops over the current contents of the array or Collection, giving you each value one at a time.  The variable in a for-each is not a proxy for an array or Collection reference.  The compiler does not replace your "i" (from "int i") with "array[index]".

If you have an array of Date, for example, and try this, the code:
Date[] array = new Date[5];
for (Date d : array) {
    d = new Date();
}
would be translated to something like this:
Date[] array = new Date[5];
for (int i = 0; i < array.length; i++) {
    Date d = array[i];
    d = new Date();
}
which as you can see will not initialize the array.  You will end up with an array containing all nulls.

NOTE:  I took the code above, compiled it into a .class file, and then used jad to decompile it.  This process gives me the following code, generated by the Sun Java compiler (1.6) from the code above:
int array[] = new int[5];
int ai[];
int k = (ai = array).length;
for(int j = 0; j < k; j++)
{
    int i = ai[j];
    i = 5;
}


                        
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