e617. Determining the Opposite Component of a Focus Event

The opposite component is the other component affected in a focus event. Specifically, in a focus-lost event, the opposite component is the one gaining the focus. In a focus-gain event, the opposite component is the one losing the focus.

Sometimes the opposite component is null, which indicates that the component is in some other application.

component.addFocusListener(new MyFocusListener());

    public class MyFocusListener extends FocusAdapter {
        public void focusGained(FocusEvent evt) {
            // The component that lost the focus
            Component c = evt.getOppositeComponent();
        }

        public void focusLost(FocusEvent evt) {
            // The component that gained the focus
            Component c = evt.getOppositeComponent();
        }
    }

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