Assigning variables with dynamic names in Java

Question

I'd like to assign a set of variables in java as follows:

int n1,n2,n3;  for(int i=1;i<4;i++) {     n<i> = 5; } 

How can I achieve this in Java?

Answer 1

This is not how you do things in Java. There are no dynamic variables in Java. Java variables have to be declared in the source code¹.

Depending on what you are trying to achieve, you should use an array, a List or a Map; e.g.

int n[] = new int[3]; for (int i = 0; i < 3; i++) {     n[i] = 5; }  List<Integer> n = new ArrayList<Integer>(); for (int i = 1; i < 4; i++) {     n.add(5); }  Map<String, Integer> n = new HashMap<String, Integer>(); for (int i = 1; i < 4; i++) {     n.put("n" + i, 5); } 

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It is possible to use reflection to dynamically refer to variables that have been declared in the source code. However, this only works for variables that are class members (i.e. static and instance fields). It doesn't work for local variables. See @fyr's "quick and dirty" example.

However doing this kind of thing unnecessarily in Java is a bad idea. It is inefficient, the code is more complicated, and since you are relying on runtime checking it is more fragile. And this is not "variables with dynamic names". It is better described as dynamic access to variables with static names.

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^{1 - That statement is slightly inaccurate. If you use BCEL or ASM, you can "declare" the variables in the bytecode file. But don't do it! That way lies madness!}