相关疑难解决方法(0)

什么是'instanceof'运算符用于？

我了解到Java有instanceof运营商.你能详细说明它的使用地点和优势吗？

我有一个swing应用程序,我在JPanel中显示图像.如果应用程序无法生成图像,我想从JPanel中删除前一个图像,并将其替换为JTextField和消息.我可以添加文本字段,但它是在前面的内容之上绘制的,它本身就是JPanel的子类.这就是我所拥有的:

private void displayMessage(String message) {
  JTextField tf = new JTextField(message);
  cdPanel.removeAll();
  cdPanel.add(tf, BorderLayout.NORTH);//tried lots of variations, inc. no layout    
  cdPanel.validate();
}

如何让cdPanel完全重绘？

要求是我有2个面板,即.Panel1,Panel2.Panel1将有2个按钮,当我点击任何按钮时,Panel应该动态显示Panel1上特定于该按钮的组件.

public class ListenerForRadioButton implements ActionListener{

JButton browseGlobal;
JFrame ParentFrame = new JFrame("Bla-Bla");
JPanel ChildPanel2 = new JPanel();
JButton upload ;

public ListenerForRadioButton(JFrame JFrameConstructor, JPanel JPanelConstructor, JButton uploadConstructor ){
    this.ParentFrame = JFrameConstructor;
    this.ChildPanel2 = JPanelConstructor;
    this.upload = uploadConstructor;
}

public void actionPerformed(ActionEvent event){

    //ChildPanel2.remove(upload);
    ChildPanel2.remove(upload);
    System.out.println("My listener is called");

} //方法结束} //结束

公共类Create_JFrame扩展了JFrame {

public Create_JFrame(){

     //Create a Frame
     JFrame ParentFrame = new JFrame("Bla-Bla");
     JPanel ChildPanel1 = new JPanel();
     JPanel ChildPanel2 = new JPanel();
     JButton Option1 = new JButton("Option1");
     JButton …