CODEWITHSUNDEEP
javaarrays
ufk
ufk

Reputation: 32104

java: how can I create a dynamic array without forcing the type of the values?

I need to create a dynamic array in Java, but the values type differ from String to Int to float. how can I create a dynamic list that I don't need to give it in advanced the type of the values?

The keys just need to be ascending numbers (1,2,3,4 or 0,1,2,3,4)

I checked ArrayList but it seems that I have to give it a fixed type for the values.

thanks!

Upvotes: 5

Views: 6671

Answers (4)

polygenelubricants
polygenelubricants

Reputation: 383746

It's more trouble than it's worth, but it is possible to interact with arrays reflectively.

import java.lang.reflect.Array;
// ...

Object arr = Array.newInstance(int.class, 10);

System.out.println(arr.getClass().getName()); // prints "[I"
System.out.println(Array.getLength(arr)); // prints "10"

Array.set(arr, 5, 42);

if (arr instanceof int[]) {
    int[] nums = (int[]) arr;
    System.out.println(nums[5]); // prints "42"
}

References

Do note that in the API you pass arrays as Object. This is because Object is the superclass of all array types, be it int[].class or String[][].class. This also means that there is little compile time safety (as is true with reflection in general). Array.getLength("mamamia") compiles just fine; it'll throw an IllegalArgumentException at runtime.

Upvotes: 1

Carl Manaster
Carl Manaster

Reputation: 40336

It's pretty rare, in my experience, to want a List<Object>. I think it might be a design smell, and I'd examine the design to see if another set of structures might better represent your data. Without knowing anything about what you're trying to solve, it's hard to say with any confidence, but typically one wants to do things with what one has put into a list, and to do anything meaningful with things once they're just Object, you'll need to examine their type and get reflective, to kind of break away from language basics. Versus storing them in more type-sensitive structures, where you can deal directly with them in their original types without reflection magic.

Upvotes: 2

Daniel Rikowski
Daniel Rikowski

Reputation: 72514

You can use this:

List<Object> myList = new ArrayList<Object>();

Integer i = 1;
Double d = 1.2;
String s = "Hello World";

myList.add(i);
myList.add(d);
myList.add(s);

Upvotes: 2

Anthony Forloney
Anthony Forloney

Reputation: 91786

You can have an array or an ArrayList of Objects which will allow you to contain String, int, and float elements.

Upvotes: 4

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