GUI 无法将 () JLabel 添加到 JFrame

Question

I am just new to Java. When I run the program below I get nothing - no JLabel is added to the window

  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import java.awt.FlowLayout;

  public class MainProgram{

  public static void main(String[] args) {
    JFrame frame = new JFrame("This is the title of the window");//adding the JFrame or window
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//so it really and literally close when we 
    //hit the close button on the window
    frame.setVisible(true);//setting the visibility
    //adding the label
    JLabel label_1 = new JLabel("this is a JLabel");
    //adding the label to the window
    label_1.setToolTipText("This is the tool tip");
    add(label_1);
}
}

Any suggestions?

Answer 1

First of all, this is wrong code.

public class MainProgram extends { // extends What?

But, what you are doing wrong is that you are adding the JLabel to whatever you extend, and not to your frame . So, change this line:

add(label_1);

to

frame.add(label_1);

Answer 2

You need add your component to your frame frame.add(label_1); and set the dimension of your frame

Answer 3

just add this line

frame.pack(); 

try to set a dimension to the jlabel and the frame itself; when using add(Component) don't to forget frame before it, use it as following : frame.add(yourLabel);