Thread: List with ArrayList

I have done this many times before and now I am getting a weird error. Say "Type is not generic", I have all the necessary imports, I do not get it...???

JPanel numberButton(JPanel panel)
	{
		List<JButton> buttons = new ArrayList<JButton>(12);
 
		for(int i=0;i<12;i++)
		{
			buttons[i] = i;
			buttons.add(new JButton());
                        panel.add(buttons[i]);
		}
 
		return panel;
	}

I am just messing around with new better ways to make buttons.

It is a very small program so I will post the whole thing. The error says "Type is not generic" when I take my mouse and put it under the red line that is under List.

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	The type List is not generic; it cannot be parameterized with arguments <JButton>
 
	at testButtonsLoop.TestButton.numberButton(TestButton.java:34)
	at testButtonsLoop.TestButton.<init>(TestButton.java:24)
	at testButtonsLoop.TestButton.main(TestButton.java:48)

package testButtonsLoop;
 
import java.awt.FlowLayout;
import java.awt.List;
import java.util.ArrayList;
 
import javax.swing.*;
 
 
public class TestButton 
{
	JFrame frame;
 
	TestButton()
	{
		frame=new JFrame();
		frame.setSize(250,350);
		frame.setLayout(new FlowLayout());
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		JPanel panel = new JPanel();
 
		//gets panel from numberButton method
		panel = numberButton(panel);
 
		frame.add(panel);
 
		frame.setVisible(true);
	}
 
	//creates a matrix of buttons and sets them into a list.
	JPanel numberButton(JPanel panel)
	{
		List<JButton> buttons = new ArrayList<JButton>(12);
 
		for(int i=0;i<12;i++)
		{
			buttons[i] = i;
			buttons.add(new JButton());
			panel.add(buttons[i]);
		}
 
		return panel;
	}
 
	public static void main(String[] args)
	{
		new TestButton();
 
	}
 
}

This code doesn't make a lot of sense. Your buttons variable is a List, so why are you using the array index operator [i] on it?

I am experimenting here, I am trying to find a good way to make buttons name them 1-12 and set there values to be displayed 1-12. Then I was going to string names...

As I wrote this it just dawned on me that I should create a string array and loop through it assigning its values to the button...

like this:

//creates a matrix of buttons and sets them into a list.
	JPanel numberButton(JPanel panel)
	{
		String[] names = {"1","2","3","4","5","6"};
		List<JButton> buttons = new ArrayList<JButton>(6); //Error on this line
 
		for(int i=0;i<6;i++)
		{
			buttons[i] = names[i];
			buttons.add(new JButton());
			panel.add(buttons[i]);
		}
 
		return panel;
	}

Ahhhh.. Thank you

JPanel numberButton(JPanel panel)
	{
		String[] names = {"1","2","3","4","5","6"};
		List<JButton> buttons = new ArrayList<JButton>(6);
 
		for(int i=0;i<6;i++)
		{
			buttons.add(new JButton(names[i]));
			panel.add(buttons.get(i));
		}
 
		return panel;
	}

I thought about what you said and I changed a few things... Now I am having a different issue as well. I read the API and it appears I am implementing it correctly.

frame.add(panel,FlowLayout.CENTER);

Gives me the following error

Exception in thread "main" java.lang.IllegalArgumentException: illegal component position
	at java.awt.Container.addImpl(Container.java:1080)
	at java.awt.Container.add(Container.java:998)
	at javax.swing.JFrame.addImpl(JFrame.java:562)
	at java.awt.Container.add(Container.java:460)
	at testButtonsLoop.TestButton.<init>(TestButton.java:29)
	at testButtonsLoop.TestButton.main(TestButton.java:55)

package testButtonsLoop;
 
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout;
 
 
import javax.swing.*;
 
 
public class TestButton 
{
	JFrame frame;
 
	TestButton()
	{
		frame=new JFrame();
		frame.setSize(250,350);
		frame.setLayout(new FlowLayout());
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		JPanel panel = new JPanel();
 
		//gets panel from numberButton method
		panel = numberButton(panel);//
 
		//centers panel onto middle of frame
		frame.add(panel,FlowLayout.CENTER);//error here but fine is I remove FlowLayout.CENTER
 
		frame.setVisible(true);
	}
 
	//creates a matrix of buttons and sets them into a list.
	JPanel numberButton(JPanel panel)
	{
		String[] names = {"1","2","3","4","5","6"};
 
		for(int i=0;i<6;i++)
		{
			JButton[] b = new JButton[6];
			b[i] = new JButton(names[i]);
			b[i].setPreferredSize(new Dimension(50,25));
 
			panel.add(b[i]);
		}
 
		panel.setLayout(new GridLayout(3,3));
		panel.setBackground(Color.BLACK);
		return panel;
	}
 
	public static void main(String[] args)
	{
		new TestButton();
 
	}
 
}

Error is coming from line 29

Centering the panel onto the frame... Obviously it's not doing what I thought

I am even trying to use BorderLayout and this is my issue. The buttons are huge despite me setting there size. They are the correct size when I use FLowLayout(). However when I try to center them I get errors as I already stated in post #7. Now I am using BorderLayout and the whole whole covered by huge buttons.

package testButtonsLoop;
 
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout;
 
import javax.swing.*;
 
 
public class TestButton 
{
	JFrame frame;
 
	TestButton()
	{
		frame=new JFrame();
		frame.setSize(250,350);
		frame.setLayout(new BorderLayout());
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		JPanel panel = new JPanel();
		JPanel textPanel = new JPanel();
 
		//gets panel from numberButton method
		panel = numberButton(panel);
		textPanel = textBox(textPanel);
 
		//get a JTextField from method and sets it to top of JFrame
		frame.add(textPanel,BorderLayout.NORTH);
		//centers panel onto middle of frame
		frame.add(panel,BorderLayout.CENTER);
 
 
		frame.setVisible(true);
	}
 
	//creates a matrix of buttons and sets them into a list.
	JPanel numberButton(JPanel panel)
	{
		String[] names = {"1","2","3","4","5","6"};
 
		for(int i=0;i<6;i++)
		{
			JButton[] b = new JButton[6];
			b[i] = new JButton(names[i]);
			b[i].setPreferredSize(new Dimension(50,25));
 
			panel.add(b[i]);
		}
 
		panel.setLayout(new GridLayout(3,3));
		panel.setBackground(Color.BLACK);
		return panel;
	}
 
	JPanel textBox(JPanel panel)
	{
		JTextField textBox = new JTextField(12);
		textBox.setPreferredSize(new Dimension(15,22));
 
		panel.add(textBox);
 
		return panel;
	}
 
	public static void main(String[] args)
	{
		new TestButton();
 
	}
 
}

You use the GridLayout. The GridLayout makes the components as big as fits the grid.
You should probably use a different layout within your button panel if you want the buttons to have a different size.

By the way, setting PreferredSize is a very ugly way of doing things and is not recommended.

I used flowLayout inside the Panel and just resized the Frame in the constructor so the buttons are where I want. I was just thought or hoped there was a better way to make a matrix of buttons.

Of course there is, get a better layout.