为什么JAVA的foreach不改变元素值？ [英] Why JAVA foreach doesn't change element value?

问题描述

下面怎么打印老板而不是低音？

 字符串boss =boss; 
 char [] array = boss.toCharArray（）; （char c：array）
 
 
 {
 if（c =='o'）
 c ='a'; 
 
 System.out.println（new String（array））; //如何不打印低音？它打印老板。 
  

您正在更改迭代变量<$ c $ ç> C 。这不会改变数组的内容。迭代变量只是数组元素的一个拷贝。如果你想修改数组，你需要明确地这样做：

$ $ $ $ $ $ $ $ $ $ c $ for（int i = 0; i< array .length; i ++）{
if（array [i] =='o'）{
array [i] ='a';

你的原始代码是等价的（按照 JLS第14.14.2节）：

  for（int i = 0; i< array.length; i ++）{
 char c = array [i ]。 
 if（c =='o'）{
 c ='a'; 
 
 
 
 
 $ b 
改变局部变量的值不会改变任何东西否则 - 只是改变局部变量。作业： 
 
 
  char c = array [i]; 
  
 拷贝数组中的值变成局部变量。它不会将本地变量与数组元素永久关联。
 
How come the following prints boss and not bass? 
String boss = "boss";
char[] array = boss.toCharArray();

for(char c : array)
{
 if (c== 'o')
     c = 'a'; 
}
System.out.println(new String(array)); //How come this does NOT print out bass?It prints boss.

解决方案
You're changing the iteration variable c. That doesn't change the contents of the array. The iteration variable is just a copy of the array element. If you want to modify the array, you need to do so explicitly:
for (int i = 0; i < array.length; i++) {
    if (array[i] == 'o') {
        array[i] = 'a';
    }
}
Your original code is equivalent (as per section 14.14.2 of the JLS) to:
for (int i = 0; i < array.length; i++) {
    char c = array[i];
    if (c == 'o') {
        c = 'a'; 
    }
}
Changing the value of a local variable will never change anything else - it just changes the local variable. The assignment:
char c = array[i];
copies the value in the array into a local variable. It doesn't associate the local variable with the array element perpetually.

                        
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