Handling keyboard events with KeyListener in TextField

KeyListener, TextField

Sometimes there is a need to perform certain actions by keys pressing in the TextField . Next, let's see how you can handle events that come from the keyboard.

First we create JTextField

JTextField textField = new JTextField();

place it on the panel or frame

panel.add(textField);

Now you need to add a listener that will be called every time when you type data in TextField. We will use KeyListener interface from the java.awt.event.

The KeyListener interface has 3 methods:

• void keyPressed (KeyEvent e);

It is called when the user presses any key.

• void keyReleased (KeyEvent e);

It is called after the user presses and releases any key.

• void keyTyped (KeyEvent e);

It is activated every time the user type the Unicode characters.

Table of Unicode characters

You can add a listener interface in two ways:

1) implement this interface and all its methods;

numberOfRouteTextField.addKeyListener(new KeyListener() {
 
    public void keyPressed(KeyEvent event) {
    ... ... ... 
    }
    public void keyReleased(KeyEvent event) {
    ... ... ... 
    }
    public void keyTyped(KeyEvent event) {
    ... ... ... 
    }
});

2) extend the abstract class of KeyAdapter , redefining only the necessary methods.

numberOfRouteTextField.addKeyListener(new NumberKeyListener());
 
class NumberKeyListener extends KeyAdapter {
    public void keyReleased(KeyEvent e) {
    ... ... ...  
    }
}

Besides, we can make the event called when you press a particular key. Each character, number, letter and control keys on the keyboard have their own code (key code). Add a check in any of the overridden methods. For example, the body of the method will be executed after the user presses the Enter key only:

public void keyReleased(KeyEvent event) {
    if(event.getKeyCode() == KeyEvent.VK_ENTER ) {
    // тело метода
    }
}

Below is an example of a small implementation. What do I want to receive?

I have a TextField field is named numberOfRouteTextField. The user types the number of paths. Then, right after the number is entered, a table with the number of lines equal to the entered number appears.

import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
 
public class Routes {
 
    private JTextField numberOfRouteTextField;
    private DefaultTableModel tableModel;
    private Frame frame;
    private ArrayList<String[]> dataOfTableAboutRoutes;
 
    public static void main(String args[]) {
 
        Routes routes = new Routes();
        routes.CreateGui();
    }
 
    private void CreateGui() {
 
        frame = new JFrame("Building a route table");
        JLabel numberOfRoutesLabel;
        JPanel widgetPanel = new JPanel();                      // create a panel where all the elements will be located
        GridBagLayout gblWidgetPanel = new GridBagLayout();     // define the layout manager
        GridBagConstraints constraints = new GridBagConstraints();
        widgetPanel.setLayout(gblWidgetPanel);
 
        numberOfRoutesLabel = new JLabel("Number of routes:");
        constraints.gridwidth = 1;   // how many cells the object occupies
        constraints.gridy = 0;       //  which vertical cell counts
        gblWidgetPanel.setConstraints(numberOfRoutesLabel, constraints);
        widgetPanel.add(numberOfRoutesLabel);
 
        numberOfRouteTextField = new JTextField(10);
        constraints.gridy = 1;
        numberOfRouteTextField.addKeyListener(new NumberKeyListener()); // add the listener to the TextField
        gblWidgetPanel.setConstraints(numberOfRouteTextField, constraints);
        widgetPanel.add(numberOfRouteTextField);           // place on the panel
 
        dataOfTableAboutRoutes = new ArrayList<>();   // here all the contents of the table will be stored
        tableModel = new DefaultTableModel();
        JTable writingRoutesTable = new JTable(tableModel);
        constraints.gridy = 2;          // how many cells does the table occupy
        gblWidgetPanel.setConstraints(writingRoutesTable, constraints);
        widgetPanel.add(writingRoutesTable);
 
        frame.add(BorderLayout.WEST,widgetPanel);
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
 
    class NumberKeyListener extends KeyAdapter {   // extend the abstract class of KeyAdapter
 
        public void keyReleased(KeyEvent event) {  // redefine necessary methods
 
            // This method will work after the user enters any character from the keyboard
            // it would be nice to do a check on the input data, so that it's only integers
 
            if (event.getKeyCode() != KeyEvent.VK_BACK_SPACE) {
 
                // If the user pressed BackSpace with the desire to erase the contents, the body of the function will not be executed
 
                String[] columnNames = new String[]{"Route number", "Start", "Finish"}; // set table headers
                int numberOfRoutes = Integer.parseInt(numberOfRouteTextField.getText());  // get the number from TextField
 
                for (int i = 0; i < dataOfTableAboutRoutes.size(); i++) {
                    tableModel.removeRow(0);
                    // after removal, the elements are shifted, so each time we delete the first element
                }
                dataOfTableAboutRoutes.clear();  // clear the contents of the table
 
                for (int i = 1; i <= numberOfRoutes; i++) {
                    String[] temp = {"route " + i, "",""};
                    dataOfTableAboutRoutes.add(temp); // enter the number of rows in the table equal to the given number
                }
                tableModel.setColumnIdentifiers(columnNames); // set the table headers
                for (String[] dataOfTable : dataOfTableAboutRoutes) {
                    tableModel.addRow(dataOfTable);    // put the contents of the ArrayList into the table
                }
            }
        }
    }
}

You can see work of program on following images.