e617. determining the opposite component of a focus event.txt

这里面包含了一百多个JAVA源文件

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();
        }
    }