Java Reference

Java passes parameters by reference which brings convinience as well as strange errors. For example:

import java.util.*;

public class Test {
	public static void main(String[] args) {
		Vector v = new Vector();
		int [] a = new int[5];
		for(int i=0;i<10;i++) {
			for(int j=0;j<5;j++) a[j] = i*j;
			v.add(new Obj(a)); // this won't work!
		}
		for(Iterator it=v.iterator();it.hasNext();) {
			it.next().dump();
		}
	}
}

class Obj {
	int [] a;
	Obj(int [] a) {
		this.a = a;
	}
	void dump() {
		for(int i=0;i		System.out.println();
	}
}

Well, the line

v.add(new Obj(a));

won't work as expected. Instead all arrays 'a' in 'Obj' are the same.

Change it to

v.add(new Obj(a.clone()));

so that every time a new array is passed.