Java: Updating a GUI element in an ArrayList

Question

I have to create a game for my final Java school assignment. In it I'm populating a JPanel with custom made "Peg" objects that extend JComponent in a for loop. The JPanel uses a GridBagLayout . Inside the for loop I add the "Peg" objects to an ArrayList , and then get the element from that ArrayList and add it to the JPanel . This is all done in a method that looks like this:

public void createDummyPegs()
{
    for (int i = 0; i < 13; i++)
    {
        initPegsArray.add(new ArrayList<>());
        dummyPegsConstraints.gridy = i;

        for (int j = 0; j < 5; j++)
        {
            dummyPegsConstraints.gridx = j;

            if (i == 0)
            {
                tempColorPeg = new ColorPeg(Color.DARK_GRAY);
                initPegsArray.get(i).add(j, tempColorPeg);
                pegsLeftPanel.add((JComponent) initPegsArray.get(i).get(j),
                                   dummyPegsConstraints);
            }
            else
            {
                tempDummyPeg = new DummyPeg();
                initPegsArray.get(i).add(j, tempDummyPeg);
                pegsLeftPanel.add((JComponent) initPegsArray.get(i).get(j), 
                                   dummyPegsConstraints); 
            }
        }
    }
}

This works fine, and it generates a grid of these "Peg" objects nicely. Here's the problem: I have a button that ideally is supposed to replace one of these "Peg" objects with another "Peg" object of a different color. When I click on the button I:

• Create new "Peg" object with the new different color;
• Remove an element from the ArrayList , let's the first one;
• Add the new "Peg" to the position where the old "Peg" used to be (assuming of course that it will ultimately reside where the old "Peg" used to be and everything else would be shifted to the right by 1.

Alternatively, I've tried using the set() method to just update the element in the given position with the new "Peg". The thing is that when I add the new "Peg" element, it seems that it is not initialized with a size. Sending this new "Peg" to a System.out.println() statement to read what's inside of it, it prints out:

com.rburgos.mastermindtestlayout.ColorPeg[,0,0,0x0,invalid,alignmentX=0.0,alignmentY=0.0,border=,flags=0,maximumSize=,minimumSize=,preferredSize=]

I don't understand why the first time I add to the ArrayList it works, but the second time it doesn't.

Any tips of guidance will be greatly appreciated. Here's the full code if that helps:

• Main program
• DummyPeg.java
• ColorPeg.java

Answer 1

I feel silly, but I think I was able to figure it out. After adding a new "Peg" to the array and passing that to the JPanel, I was calling update() . By calling revalidate() now the new "Peg" gets added to the panel. Hopefully this will help others with a similar problem.