Java Tetris

[dave dal]

Hi there,
I have a question as to why JPanel's work the way this certain way. When I try and make GUI applications or games, I always try to make the centered display JPanel through a different class that extends JPanel.
I've literally just started a Tetris demo, and I decided to make a MainScreen class that extends JPanel. And I add an instance of MainScreen to the center of the original JPanel(Tetrisgame class). I first create an instance of the MainScreen JPanel called screen. I then create an instance of BlockPart called bp. And I invoke screen.addPartToScreenAt(2,2,bp) - the method's function is to add the parameter bp(instance of BlockPart) to the MainScreen JPanel at coordinates 2,2. I do this so that I can see a new JPanel - namely a BlockPart - on the MainScreen. I just want to test that I can actually change the JPanels from separate classes by attempting to display one simple BlockPart(JPanel) on the screen! Assistance?


Code that I did not provide but it irrelevant:
-Main class that creates JFrame window.
-Block contains an array of BlockParts that will eventually be a combination of blockparts that create the conventional Tetris blocks.

//Tetrisgame class
package tetris_pack;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class Tetrisgame extends JPanel{
	private MainScreen screen; //main screen that displays the game
	public Tetrisgame(){
		setLayout(new BorderLayout());
		
		screen = new MainScreen();
		BlockPart bp= new BlockPart(Color.green);
		screen.addPartToScreenAt(2,2,bp);
		add(screen,BorderLayout.CENTER);
		setPreferredSize(new Dimension(500,600));
	}
	
}


//MainScreen Class

package tetris_pack;
import java.awt.GridLayout;
import javax.swing.JPanel;

public class MainScreen extends JPanel{	
	private JPanel[][] grid = new JPanel[10][20];
	public MainScreen(){
		setLayout(new GridLayout(10,20));
		for (int x = 0; x < grid.length; x++){
			for (int y = 0; y < grid[x].length; y++){
				grid[x][y] = new JPanel();
				add(grid[x][y]);
			}
		}
	}//end of constructor
	
	public void addPartToScreenAt(int x, int y, BlockPart bp){
		grid[x][y] = bp;
		repaint();
		revalidate();
	}
	public void addBlockToScreenAt(int x, int y, Block b){
		
	}
}




//BlockPart class
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class BlockPart extends JPanel{
	public BlockPart(Color c){
		setBackground(c);
	}
}

,
Nightingale

[Wendy Gibbons]

so your green panel isn't appearing on the main panel?

you store it in the array of jpanels (grid) but do you actually add it to the main panel?

[dave dal]

I believe I do! add(grid[x][y]) should add it to the main panel.

[Rob Spoor]

You add empty JPanels, yes. But in your addPartToScreenAt method you don't remove one of those JPanels and add the BlockPart. A quick and untested fix:

	public void addPartToScreenAt(int x, int y, BlockPart bp){
		remove(grid.length * x + y); // remove the previous panel at that location
		grid[x][y] = bp;
		add(bp, grid.length * x + y); // add the new panel at that location
		repaint();
		revalidate();
	}

Also, a small improvement:

dave dal wrote:

	public Tetrisgame(){
		setLayout(new BorderLayout());
...
	public MainScreen(){
		setLayout(new GridLayout(10,20));

Instead of calling setLayout(...), call super(...). Right now these constructors implicitly call super() which sets a FlowLayout. Afterwards you immediately overwrite that with the actual layout. By calling the super class constructor with a layout you skip the FlowLayout.

[dave dal]

Wow thank you so much for your help, guys. Yes. I've been studying java, c++, and python for only a year and a half now. But these GUI concepts really help me understand many classes that I have not already learned!

[Rob Spoor]

You're welcome.