屏幕上没有显示Java Swing应用程序

Question

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class SimultaneousSolver extends JFrame implements ActionListener
{

    JTextField  tfEQ1X  = new JTextField (20);
    JTextField  tfEQ1Y  = new JTextField (20);
    JTextField  tfEQ1Num    = new JTextField (20);

    JTextField  tfEQ2X  = new JTextField (20);
    JTextField  tfEQ2Y  = new JTextField (20);
    JTextField  tfEQ2Num    = new JTextField (20);

    JLabel lblX1 = new JLabel ("X₁");
    JLabel lblY1 = new JLabel ("Y₁");
    JLabel lblNum1  = new JLabel ("Number₁");
    JLabel lblEqual1 = new JLabel ("=");

    JLabel lblX2 = new JLabel ("X₂");
    JLabel lblY2 = new JLabel ("Y₂");
    JLabel lblNum2  = new JLabel ("Number₂");
    JLabel lblEqual2 = new JLabel ("=");

    JTextArea Empty = new JTextArea ("",1,20);

    double X1, X2, Y1, Y2, Num1, Num2;
    double SolX, SolY;

    Font font = new Font("Comic Sans MS", Font.BOLD, 14);

    SimultaneousSolver()
    {
        super ("Simultaneous Equation Solver");
        setDesign();
        setSize(700,400);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        JPanel panelEquation1 = new JPanel(new GridLayout(1,7));
        {
            panelEquation1.add(lblX1);
            panelEquation1.add(tfEQ1X);
            panelEquation1.add(lblY1);
            panelEquation1.add(tfEQ1Y);
            panelEquation1.add(lblEqual1);
            panelEquation1.add(lblNum1);
            panelEquation1.add(tfEQ1Num);
        }

        JPanel panelEquation2 = new JPanel(new GridLayout(1,7));
        {
            panelEquation2.add(lblX2);
            panelEquation2.add(tfEQ2X);
            panelEquation2.add(lblY2);
            panelEquation2.add(tfEQ2Y);
            panelEquation2.add(lblEqual2);
            panelEquation2.add(lblNum2);
            panelEquation2.add(tfEQ2Num);
        }

        setVisible(true);
    }


    public final void setDesign() 
    {
        try 
        {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        }   
        catch(Exception e) 
        {   
        }
    }

    public static void main(String[] args)
    {
        new SimultaneousSolver();
    }

}

好吧，所以我正在使用纯粹的swing开始一个新的应用程序开发，所以我设置了我的对象和东西，当我尝试运行应用程序以查看它是否看起来不错时，除了空容器外什么都没有显示。

Answer 1

在构造函数的末尾添加这两行。

setLayout(new GridLayout());  // sets layout for frame - you can choose any one suitable layout
add(panelEquation1);  // adds 1st panel
add(panelEquation2); // adds 2nd panel