What is the difference between int and Integer in this script?

Question

import java.util.Arrays; import java.util.List; import java.util.ArrayList; public class arraysAsList { public static void main(String[] args) { String [] arrayA = {"Box","Sun","Clock","Phone"}; Integer [] arrayB = {21,27,24,7}; List listStructureA = new ArrayList(); List listStructureB = new ArrayList(); listStructureA = Arrays.asList(arrayA); listStructureB = Arrays.asList(arrayB); System.out.println("My first list : " + listStructureA); System.out.println("Sun = " + listStructureA.get(1)); System.out.println("My second list : " + listStructureB); System.out.println("24 = " + listStructureB.get(2)); } }

I realize int is a primitive type and Integer is a class. But in this script, when i try to use int instead of Integer, i get 'index out of bounds exception' error. I used int to create arrays before, what's the difference between int arrays and Integer arrays? Thanks in advance.

Rohit Jain · Accepted Answer · 2013-10-12 10:57:43Z

Arrays.asList(T...) takes varargs. When you pass Integer[], type T is inferred as Integer, each element of the Integer[] is unpacked as different argument of varargs.

However, when you pass an int[], since int is not an object, T is inferred as int[]. So, what is passed to the method is a single element array, with value int[]. So, the number of varargs is different in both the cases. Hence, accessing index 1 will give you error, when you pass int[].

So, in one line - Integer[] is an array of references to objects, whereas, int[] is itself an object.

You can do a simple test, with this method:

public static <T> void test(T... args) { System.out.println(args.length); }

Then call this method as:

int[] arr = {1, 2, 3}; Integer[] arr2 = {1, 2, 3}; test(arr); // passing `int[]`. length is 1 test(arr2); // passing `Integer[]`. length is 3

Collectives™ on Stack Overflow

What is the difference between int and Integer in this script?

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related