In this tutorial we are going to see how to handle focus changed in a Java Desktop Application. You might find this particularly useful if you have an application that contains many objects and you want to monitor the focus changes over these objects, if you always want to know the object that the user interacts with. You can use that kind of information when you want your application to behave differently in some aspects according to which window the user is working on.
Basically, to handle focus changes in a Java application, one should follows these steps:
- Create a new
FocusAdapterinstance. - Override
focusGainedmethod in order to customize the handling of that event. Now every time an object gains focus, this method will fire up. - Override
focusLostmethod to customize the handling of that event. Now every time an object looses focus, this method will fire up. - Use
addFocusListenerof a specific component in order to add to it the aboveFocusAdapter.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.desktop;
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Frame;
import java.awt.TextArea;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
public class FocusListener {
public static void main(String[] args) {
// Create frame with specific title
Frame frame = new Frame("Example Frame");
// Create a component to add to the frame; in this case a text area with sample text
final TextArea textArea = new TextArea("Click button to check its focus status...");
// Create a component to add to the frame; in this case a button
Button button = new Button("Click Me!!");
// Add a focus listener to handle focus changes
button.addFocusListener(new FocusAdapter() {
public void focusGained(FocusEvent evt) {
textArea.setText(textArea.getText() + "nButton focus gained");
}
public void focusLost(FocusEvent evt) {
textArea.setText(textArea.getText() + "nButton focus lost");
}
});
// Add the components to the frame; by default, the frame has a border layout
frame.add(textArea, BorderLayout.NORTH);
frame.add(button, BorderLayout.SOUTH);
// Show the frame
int width = 300;
int height = 300;
frame.setSize(width, height);
frame.setVisible(true);
}
}
This was an example on how to handle focus changes in a Java Desktop Application.
