Using ArrayList in a JPanel

Question

Class SampleFiveA extends JPanel. This contains textfields, one below the other, each of which has a label on the left. All textfields will be of the same width and positioned against the right border of the panel. SampleFiveA has only one constructor that accepts the following three parameters:

ArrayList names, ArrayList values, int cols

I so far created the sample username password screen in GUI but now I have a problem implementing an ArrayList in JPanel one for User Name and the other for password. Kind of stuck there for hours now cant find a proper example to do it. Below is the code I commented what I need to be done using ArrayList.

public class SampleFiveA extends JPanel {


ArrayList<String> names = new ArrayList<String>(); //the text for the labels
ArrayList<String> values = new ArrayList<String>(); // the initial contents of the text fields
int col ; //the number of columns used to set the width of each textfield


public SampleFiveA()
{
        JPanel p = new JPanel();
        p.setLayout(new GridLayout(2,2)); 

        JLabel lab1 = new JLabel("User Name", JLabel.LEFT);         
        p.add(lab1 = new JLabel("User Name"));
        JTextField txt1 = new JTextField("User Name", JTextField.RIGHT);
        p.add(txt1= new JTextField());



        JLabel lab2 = new JLabel("Password ", JLabel.LEFT);            
        p.add(lab2 = new JLabel("Password"));
        JPasswordField txt2 = new JPasswordField("*****",JPasswordField.RIGHT );
        p.add(txt2 = new JPasswordField());



      //  names.add(lab1,lab2);// Not right but I want to put the label text to this arrayList
      //  values.add(txt1,txt2);// 


        add(p);
};



public static void main(String[] args) 
{


JFrame frame = new JFrame();
frame.getContentPane().add(new SampleFiveA());

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200,200);
frame.setVisible(true);


};
};

Important thing to understand: you don't get to create the ArrayLists names, values, or the int cols. They're passed into your constructor, and then you assign them to your object's own variables. Your constructor's signature, then, is public SampleFiveA(ArrayList names, ArrayList values, int cols). I don't know exactly what you have to achieve here, but I suspect it'll involve reading/writing from these provided lists. — Owen
– Owen, Commented May 13, 2011 at 16:54
Do you know how to iterate over your lists? If not, read about for loops. — Jeremy
– Jeremy, Commented May 13, 2011 at 16:54

rurouni · Accepted Answer · 2011-05-13 16:54:37Z

2

you can use

names.add(txt1.getText());
values.add(txt2.getText());

but maybe you should think about a better data structure, e.g. a HashMap and

hashmap.put(txt1.getText(),txt2.getText())

(and you should do this based on some event,e.g. user presses a button, not in the constructor, as otherwise the value will be the one you set before)

answered May 13, 2011 at 16:54

rurouni

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2 Comments

rurouni Over a year ago

have a look at download.oracle.com/javase/tutorial/uiswing/examples/components/…

Splitter Over a year ago

Thanks for that !!! Yeah I should first implement some buttons then start from there.

aioobe · Accepted Answer · 2011-05-13 17:00:45Z

Here's a start for you.

It adds a FocusListener to the text fields and makes sure that the content of the ArrayList is updated with the current value when the text field looses focus.

import java.awt.GridLayout;
import java.awt.event.*;
import java.util.ArrayList;

import javax.swing.*;

public class Main extends JPanel {

    ArrayList<String> names = new ArrayList<String>(); // the text for the
                                                       // labels
    ArrayList<String> values = new ArrayList<String>(); // the initial contents
                                                        // of the text fields
    int col; // the number of columns used to set the width of each textfield

    public Main() {
        JPanel p = new JPanel();
        p.setLayout(new GridLayout(2, 2));

        names = new ArrayList<String>();
        values = new ArrayList<String>();


        JLabel lab1 = new JLabel("User Name", JLabel.LEFT);
        p.add(lab1);
        JTextField txt1 = new JTextField("User Name", JTextField.RIGHT);
        p.add(txt1);

        names.add(lab1.getText());
        values.add(txt1.getText());

        JLabel lab2 = new JLabel("Password ", JLabel.LEFT);
        p.add(lab2);
        JPasswordField txt2 = new JPasswordField("*****", JPasswordField.RIGHT);
        p.add(txt2);
        names.add(lab2.getText());
        values.add(txt2.getText());


        // names.add(lab1,lab2);// Not right but I want to put the label text to
        // this arrayList
        // values.add(txt1,txt2);//
        txt1.addFocusListener(new ArrayListFocusListener(txt1, values, 0));
        txt2.addFocusListener(new ArrayListFocusListener(txt2, values, 1));

        add(p);


        // Start a thread to print the content of the list for 10 seconds
        new Thread() {
            public void run() {
                for (int i = 0; i < 10; i++) {
                    try {
                        sleep(1000);
                    } catch (InterruptedException e) {
                    }
                    System.out.println(values);
                }
            }
        }.start();


    };



    public static void main(String[] args) {

        JFrame frame = new JFrame();
        frame.getContentPane().add(new Main());

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(200, 200);
        frame.setVisible(true);

    };

    class ArrayListFocusListener implements FocusListener {
        JTextField textField;
        ArrayList<String> backingList;
        int myIndex;

        public ArrayListFocusListener(JTextField textField,
                ArrayList<String> backingList, int myIndex) {
            this.textField = textField;
            this.backingList = backingList;
            this.myIndex = myIndex;
        }

        public void focusGained(FocusEvent e) {
        }

        @Override
        public void focusLost(FocusEvent e) {
            backingList.set(myIndex, textField.getText());
        }

    }
};

Thanks alot!!! Now I understand why I couldn't understand the examples as there was ActionListners included. I can start from here easily. Thanks again.

Dimitrios K. · Accepted Answer · 2011-05-13 17:11:15Z

1

I'm sure what you are trying to do. You either want to put the JLabel in an ArrayList or the text of that label.

If you want to put the whole JLabel in an ArrayList, you should make a ArrayList<JLabel>. But I take it you want to get the text from the JLabel, so you should write names.add(lab1.getText());.

The constructor you have made doesn't take any parameters. The parameters you have wrote are the instance variable, meaning those are the variables any instance of that class will have. If you want to pass parameters in your constructor you should do what thasc told you.

You write:

JLabel lab1 = new JLabel("User Name", JLabel.LEFT);         
p.add(lab1 = new JLabel("User Name"));

But since you are already creating the lab1 JLabel you could just write p.add(lab1).

And a final note I think SampleFiveA should better extend JFrame unless you want it to extend JPanel to use it somewhere else. If you need it to be standalone you should change that.

cheers

answered May 13, 2011 at 17:11

Dimitrios K.

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1 Comment

Splitter Over a year ago

thanks I just put it by looking at some web samples. Didnt really knew why. Thanks for the explanation.

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