Why is my code running the for loop more than 5 times?

Question

I sound really silly for asking this, but I'm having trouble with my for loop.

Here is part of the code I'm having trouble with.

Scanner input = new Scanner( System.in);
int number;
for(int i = 0;i < 5;i++) {
  System.out.print("Enter 5 integers:");
  number = input.nextInt();
}

When I run it the print out loops more than 5 times.

public class BarGraph extends JPanel
{

    public void paintComponent( Graphics g )
    {

        Scanner input = new Scanner( System.in);
       // super.paintComponent(g);
        int number;

        for(int i = 0;i < 5;i++)
        {
             System.out.print("Enter 5 integers:");
        number = input.nextInt();
       // g.drawRect(10 * i, 10 * i, 100 * number, 10);    
        }
    }
}

Running BarGraphTest

public class BarGraphTest
{
    public static void main( String[] args)
    {
        BarGraph panel = new BarGraph();
        JFrame application = new JFrame();
        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        application.add( panel );
        application.setSize( 300, 300);
        application.setVisible( true );
    }
}

Basically what I'm trying to do is read 5 integers and just display them on JPanel line a bar graph.

The culprit is `input.nextInt();`. Use `input.nextLine();` instead. — Tiny, Apr 01 '14 at 15:04
It should run only 5 times (or less if you don't type integer values as inputs). Are you sure about the code you posted? — Mena, Apr 01 '14 at 15:05
@Tiny: `nextLine` produces a `String`. Need to parse the integer. — Engineer2021, Apr 01 '14 at 15:05
@Tiny: `nextInt` will work fine in this example.. now if he had a bunch of them, that's a different story.. you can iterate over them and `nextLine` would be helpful. — Engineer2021, Apr 01 '14 at 15:09
Enter 5 integers:3 Enter 5 integers:4 Enter 5 integers:5 Enter 5 integers:6 Enter 5 integers:7 Enter 5 integers:8 Enter 5 integers:2 Enter 5 integers:1 Enter 5 integers:2 Enter 5 integers:4 — user3485650, Apr 01 '14 at 15:12
@user3485650 Could we see an entire class that replicates this, something strange is going on — Richard Tingle, Apr 01 '14 at 15:13
@user3485650 Print out the value of `i` in each iteration. That might give you a better clue as to what's going on. As Richard said more code would be useful - it may be that this block of code is, itself getting repeatedly executed. — Michael Berry, Apr 01 '14 at 15:13
I note that it produces exactly 10 outputs which would support a theory that this piece of code is being called twice — Richard Tingle, Apr 01 '14 at 15:15
paintComponent is called by swing ["when it needs to be"](http://stackoverflow.com/a/15545309/2187042), in this case it seems it needs 2 repaints. I personally would not mix up graphics and logic like this for exactly this kind of reason — Richard Tingle, Apr 01 '14 at 15:20

score 4 · Answer 1 · edited May 23 '17 at 12:11

You have mixed up state change with graphics. paintComponent is called by swing "when it needs to be", in this case Swing determined it needed 2 repaints, for whatever reason.

If your program is written in a way that it cares when or how often paintComponent is called you will likely have problems. You should instead only have paintComponent ask about the current state of some object and paint accordingly.

Depepending on your exact circumstances the 5 numbers should be provided in one of the following ways

Passed to the constructor of BarGraph
Requested from the user in the constructor of BarGraph (not my favourite, but would work)
Passed to a method of BarGraph
Be in some other object that is passed to BarGraph.

They absolutely should not be requested from the user inside the paintComponent, this means that every time a redraw is nessissary (e.g. moving, re-sizing, changing focus, being hidden by other frames etc) the numbers will be re-requested from the user.

You are also likely to want to start your paintComponent method with super.paintComponent(g) but that will again be situation dependant

Why is my code running the for loop more than 5 times?

1 Answers1