Question

I am fairly new to Java, and I want to generate an array of random (x,y) coordinates of length ‘number’ that contains no duplicates. x or y values can be repeated, but there must be no repeated (x,y) coordinates. The output does not have to be Points, simply some way of holding x,y values for coordinates.

I can generate an array of random points, and have tried using a Set to ensure there are no duplicate values, but have run into problems. I tried using the condition “while (set.size)” and the ‘add’ method which should disallow duplicates, to create an output of the correct size which contains unique points.

This is the code:

Set<Point> set = new HashSet<Point>();
Random position = new Random();
Point test=new Point();

do{
    test.x=position.nextInt(xx);
    test.y=position.nextInt(yy);   
    //xx and yy are the random number limits called from another part of the code
    set.add(test);     
}
while (set.size()<number);

List<Object> list = new ArrayList<Object>(set);
Object[] coord = list.toArray();

This outputs an array of the correct length, but every element is the same. Can anyone offer any help?

Thanks

Answer 1

test points to the same variable in space everytime you loop, to fix that create a new instance inside the loop – not just once before it:

Set<Point> set = new HashSet<Point>();
Random position = new Random();
Point test;

do{
    test = new Point();
    test.x=position.nextInt(xx);
    test.y=position.nextInt(yy);   
    //xx and yy are the random number limits called from another part of the code
    set.add(test);     
}
while (set.size()<number);

List<Object> list = new ArrayList<Object>(set);
Object[] coord = list.toArray();