Thread: Debugging with Print Statement (on List of Object Class)

I'm trying to debug a program with print statement. However, when I try to print the LinkedList of the program, it does not return the value. Instead, it does return me the memory address of those values I believe. How to fix it, in a way I can see the actual value. Note : I'm trying to print list containing multiple object of Interval Class.

Here is my code :

Interval Class

package Interval;
 
public class Interval {
    public int start;
    public int end;
 
    public Interval(int s, int e) {
        this.start = s;
        this.end = e;
    }
}

App (main) Class

import java.util.*;
 
import Interval.Interval;
 
public class App {
 
    public static int[][] merge(int[][] intervals) {
        if (intervals.length <= 1) { // if only one interval
            return intervals;
        }
        // add intervals to linked list
        LinkedList<Interval> ll = new LinkedList<>();
        for (int[] temp : intervals) {
            ll.add(new Interval(temp[0], temp[1])); // add each interval object with each interval from intervals array
            System.out.println("Adding new Interval object to list ll : ");
            System.out.println(ll);
        }
        System.out.println();
        // sorting list on start time
        Collections.sort(ll, new Comparator<Interval>() {
            public int compare(Interval a, Interval b) {
                return a.start - b.start;
            }
        });
        System.out.println("List ll after sorting: ");
        System.out.println(ll);
        System.out.println();
 
        LinkedList<Interval> result = new LinkedList<>();
        for (Interval curr : ll) {
            if (result.isEmpty() || result.getLast().end < curr.start) {
                result.add(curr);
                System.out.println(result);
                System.out.println();
            } else {
                result.getLast().end = Math.max(curr.end, result.getLast().end);
                System.out.println(result);
 
            }
        }
        int[][] res = new int[result.size()][2];
        int count = 0;
        for (Interval temp : result) {
            res[count][0] = temp.start;
            res[count][1] = temp.end;
            count++;
        }
        return res;
    }
 
    public static void main(String[] args) throws Exception {
        int[][] intervalNumbers = { { 1, 3 }, { 2, 6 }, { 8, 10 }, { 15, 18 } };
        int[][] intervalNumbers2 = { { 1, 3 } };
        System.out.println(Arrays.deepToString(merge(intervalNumbers)));
        // System.out.println(Arrays.deepToString(merge(intervalNumbers2)));
 
    }
}

Here is the output I got when I try to debug it.

Adding new Interval object to list ll : 
[Interval.Interval@7de26db8]
Adding new Interval object to list ll : 
[Interval.Interval@7de26db8, Interval.Interval@1175e2db]
Adding new Interval object to list ll : 
[Interval.Interval@7de26db8, Interval.Interval@1175e2db, Interval.Interval@36aa7bc2]
Adding new Interval object to list ll : 
[Interval.Interval@7de26db8, Interval.Interval@1175e2db, Interval.Interval@36aa7bc2, Interval.Interval@76ccd017]
 
List ll after sorting: 
[Interval.Interval@7de26db8, Interval.Interval@1175e2db, Interval.Interval@36aa7bc2, Interval.Interval@76ccd017]
 
[Interval.Interval@7de26db8]
 
[Interval.Interval@7de26db8]
[Interval.Interval@7de26db8, Interval.Interval@36aa7bc2]
 
[Interval.Interval@7de26db8, Interval.Interval@36aa7bc2, Interval.Interval@76ccd017]
 
[[1, 6], [8, 10], [15, 18]]

Alright, understood.

Also, I have a quick question about the behavior of the following line - You can find this line inside the first for-each loop of the program.

ll.add(new Interval(temp[0], temp[1]));

With the following entry :

int[][] intervalNumbers = { { 1, 3 }, { 2, 6 }, { 8, 10 }, { 15, 18 } };

Does that mean that temp[0] and temp[1] are being incremented by one each time via the loop?
What do index 0 and index 1 mean for the intervals array here?

If the entry was

int[][] intervalNumbers = { { 1, 3, 11 }, { 2, 6, 8}, { 8, 10, 9 }, { 15, 18, 10 } };

How would we modify that line?

int[][] intervalNumbers = { { 1, 3 }, { 2, 6 }, { 8, 10 } };
 
for (int[] temp : intervals) { 
  ll.add(new Interval(temp[0], temp[1]));
 
means, get inner arrays in loop:
  temp =  { 1, 3 }
  temp =  { 2, 6 }
  temp =  { 8, 10 }
 
and add objects with (this numbers as parameters)
  Interval( 1, 3 ) 
  Interval( 2, 6 ) 
  Interval( 8, 10 )