Events
Code low-level events
Focus

How to work with focus events

A focus event occurs when the focus moves to or from a component.
To implement a focus listener, you must implement both of the methods of the FocusListener interface.

Methods of the FocusListener interface

Method	Description
void focusGained(FocusEvent e)	Invoked when a component that implements a focus listener gains the focus.
void focusLost(FocusEvent e)	Invoked when a component that implements a focus listener loses the focus.

Common methods of the FocusEvent class

Method	Description
getComponent()	Returns the component where the event occurred.
isTemporary()	Returns true if the focus is a temporary change.
getOppositeComponent()	Returns the other component involved in the focus change. Introduced with JDK 1.4.

A method of the JTextComponent class

Method	Description
selectAll()	Selects all of the text in the text component.

A class that implements the FocusListener interface

public class AutoSelect implements FocusListener
{
    public void focusGained(FocusEvent e)
    {
        if (e.getComponent() instanceof JTextField)
        {
            JTextField t = (JTextField) e.getComponent();
            t.selectAll();
        }
    }

    public void focusLost(FocusEvent e) {}
}

A text field that uses the focus listener

paymentTextField = new JTextField(10);
paymentTextField.addFocusListener(new AutoSelect());
displayPanel.add(paymentTextField);