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Oct 27th, 2009

ArrayList<ArrayList<int>> compiler problem

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I am trying to create a 2d array list but it is giving me a compiler error pointing at the first line of the function. I don't really get what is causing the problem. I am pretty good in C++ but Java has some new rules that I am trying to learn. Does anyone see a problem here?

Code:

Java Syntax (Toggle Plain Text)
void addToList(int[] a, int j, int i, int N)            
{
	ArrayList< ArrayList<int> > perms = new ArrayList<ArrayList<int>>();
	for(int x = 0; x < N; x++) {
		perms.add(new ArrayList<int>());
		perms.get(perms.size()-1).add(a[x]);
		System.out.print(a[x]);
	}
	System.out.println("   swapped(" + j + ", " + i + ")");
} // addToList()
void addToList(int[] a, int j, int i, int N)            
{
	ArrayList< ArrayList<int> > perms = new ArrayList<ArrayList<int>>();
	for(int x = 0; x < N; x++) {
		perms.add(new ArrayList<int>());
		perms.get(perms.size()-1).add(a[x]);
		System.out.print(a[x]);
	}
	System.out.println("   swapped(" + j + ", " + i + ")");
} // addToList()

Error:

(Toggle Plain Text)

MiniMaxTree.java:119: unexpected type
found   : int
required: reference
                ArrayList< ArrayList<int> > perms = new ArrayList<ArrayList<int>>();
                                ^
MiniMaxTree.java:119: unexpected type
found   : int
required: reference
                ArrayList< ArrayList<int> > perms = new ArrayList<ArrayList<int>>();

Thanks in advance!

Last edited by chunalt787; Oct 27th, 2009 at 2:37 pm.

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chunalt787

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Oct 27th, 2009

Re: ArrayList<ArrayList<int>> compiler problem

It's annoying, but you can't use a primitive type (int/char/boolean etc) with generics.

JamesCherrill

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Oct 27th, 2009

Re: ArrayList<ArrayList<int>> compiler problem

So I would have to make a wrapper class myInt which stores an int as its data member?

chunalt787

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Re: ArrayList<ArrayList<int>> compiler problem

There are existing wrapper classes for all of the primitive types.
Use Integer. Auto-boxing will handle the casting for you.

Last edited by Ezzaral; Oct 27th, 2009 at 4:07 pm.

Ezzaral

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Re: ArrayList<ArrayList<int>> compiler problem

Ok thank you

chunalt787

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