我可以在 Java 的循环内更改变量名吗
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Can I change variable name inside a loop in Java
提问by Judy
I want to change the variable name with each iteration. Since the number of nodes created is dynamically changing.
我想在每次迭代中更改变量名称。由于创建的节点数量是动态变化的。
I tried using one dimensional array but its returning a null pointer. My code is as follow
我尝试使用一维数组，但它返回一个空指针。我的代码如下
GenericTreeNode<String> **root1[]** = null;
for(int i=0;i<10;i++)
{
String str="child"+i;
System.out.println(str);
**root1[i]** =new GenericTreeNode<String>(str);
}
I am using already built datastructure
我正在使用已经构建的数据结构
public class GenericTree<T> {
private GenericTreeNode<T> root;
public GenericTree() {
super();
}
public GenericTreeNode<T> getRoot() {
return this.root;
}
public void setRoot(GenericTreeNode<T> root) {
this.root = root;
}
Is there some other way in java or JSP to change the variable name dynamically inside the loop.
java或JSP中是否有其他方法可以在循环内动态更改变量名称。
回答by Sean Patrick Floyd
GenericTreeNode<String> root1[] = null;
This line is equivalent to this one:
这一行相当于这一行：
GenericTreeNode<String>[] root1 = null;
so you create an array variable and initialize it to null
所以你创建了一个数组变量并将其初始化为 null
root1[i] =new GenericTreeNode<String>(str);
but here you assign a value to the array's index.
但是在这里您为数组的索引分配了一个值。
This must throw a NullPointerException!!.
这必须抛出一个NullPointerException！！
Here's how to do it:
这是如何做到的：
GenericTreeNode<String>[] root1 = new GenericTreeNode<String>[10];
回答by JB Nizet
No, you can't change variable names in Java.
不，您不能在 Java 中更改变量名称。
You got a NullPointerException when using an array because you tried to put a value in the array, and the array was null. You have to initialize the array, with the right number of elements :
使用数组时出现 NullPointerException，因为您尝试在数组中放入一个值，而数组为空。您必须使用正确数量的元素初始化数组：
int length = 10;
GenericTreeNode<String>[] root1 = new GenericTreeNode<String>[length];
for (int i = 0; i < length; i++) {
String str = "child" + i;
System.out.println(str);
root1[i] = new GenericTreeNode<String>(str);
}
回答by munificent
You probably mean to do this:
你可能想这样做：
GenericTreeNode<String> root1[] = new GenericTreeNode<String>[10];
for(int i=0;i<10;i++)
{
String str="child"+i;
System.out.println(str);
root1[i] = new GenericTreeNode<String>(str);
}
There's no need to "change a variable name".
无需“更改变量名称”。
回答by Beege
No, a variable name can't be changed. Try another method like a 2-dimensional array to create another "variable" as you're iterating.
不，变量名称不能更改。尝试另一种方法，例如二维数组，在迭代时创建另一个“变量”。
回答by Judy
I not able to initiate GenericTree as array. Later I used just vector to solve the problem.
我无法将 GenericTree 作为数组启动。后来我只用vector来解决这个问题。
