e614. setting the initial focused component in a window.txt

来自「这里面包含了一百多个JAVA源文件」· 文本 代码 · 共 29 行

There is no straightforward way to set the initial focused component in a window. The typical method is to add a window listener to listen for the window opened event and then make the desired component request the focus. 
    // Create frame and three buttons
    JFrame frame = new JFrame();
    JButton component1 = new JButton("1");
    JButton component2 = new JButton("2");
    JButton component3 = new JButton("3");
    
    // Set component with initial focus; must be done before the frame is made visible
    InitialFocusSetter.setInitialFocus(frame, component2);
    
    class InitialFocusSetter {
        public static void setInitialFocus(Window w, Component c) {
            w.addWindowListener(new FocusSetter(c));
        }
    
        public static class FocusSetter extends WindowAdapter {
            Component initComp;
            FocusSetter(Component c) {
                initComp = c;
            }
            public void windowOpened(WindowEvent e) {
                initComp.requestFocus();
    
                // Since this listener is no longer needed, remove it
                e.getWindow().removeWindowListener(this);
            }
        }
    }