CODEWITHSUNDEEP
javaconstructor
vkosyj
vkosyj

Reputation: 767

return different value in constructor and in the method in java

I wonder why at place (), it returns different values. In the constructor, it returns me 3, which makes sense. However, in the second (), it returns 0. I thought both places should return 0. Am I missing something here? 

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Vector2D implements Iterator<Integer> {
    private List<List<Integer>> vec2d;
    private Iterator<Integer> it;
    private int counter = 0;
    private int size;
    public Vector2D(List<List<Integer>> vec2d) {
        this.vec2d = new ArrayList<List<Integer>>();
        if(vec2d.size() == 0) {
            this.it = null;
        } else {
            this.size = vec2d.size();
            System.out.println("this size is " + size); // * returns 3
            this.it = vec2d.get(0).iterator();   
        }
    }

    @Override
    public Integer next() {
         System.out.println("what happens here? " + vec2d.size());  **// * why it returns 0?? should it return 3??**
         if(hasNext()) {
             return it.next();
        }
        return -1;
    }

     @Override
     public boolean hasNext() {
         if(it == null) {
            return false;
        }
        while(counter < size) {
            if(it.hasNext()) {
                return true;
            }
            counter++;
            if(counter >= size) {
                return false;
            }
            System.out.println("counter is " + counter + " size is " + vec2d.size());
            List<Integer> l = vec2d.get(counter);
            it = l.iterator();
        }
        return false;
    }

    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();
        List<Integer> list2 = new ArrayList<Integer>();
        List<Integer> list3 = new ArrayList<Integer>();
        list.add(1);
        list.add(2);
        list2.add(3);
        list3.add(4);
        list3.add(5);
        list3.add(6);
        List<List<Integer>> lists = new ArrayList<List<Integer>>();
        lists.add(list);
        lists.add(list2);
        lists.add(list3);

        Vector2D vec = new Vector2D(lists);
        System.out.println(vec.next());

    }
}

Upvotes: 0

Views: 45

Answers (1)

J&#233;r&#244;me
J&#233;r&#244;me

Reputation: 1254

You have to assign your attribute the value from constructor parameter otherwise you are working with the Parameter vec2d and not with your Attribute vec2d:

public Vector2D(List<List<Integer>> vec2d) {
    this.vec2d = vec2d;//assign Parameter to list
    if(this.vec2d.size() == 0) {
        this.it = null;
    } else {
        this.size = this.vec2d.size();
        System.out.println("this size is " + size); // * returns 3
        this.it = this.vec2d.get(0).iterator();   
    }
}

Just try to rename the List<List<Integer>> vec2d method param to something else and you will see.

Upvotes: 3

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