简易计算器

import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class Desktop extends JFrame {
    private Container container = this.getContentPane();
    private GridBagLayout gridBagLayout = new GridBagLayout();
    private GridBagConstraints gridBagConstraints = new GridBagConstraints();
    private JTextField displayField;
    private String lastCommand = "=";
    private double result = 0.0d;
    private boolean start = true;

    public Desktop() {
        super("JAVA图形化界面计算器");
        container.setLayout(gridBagLayout);
        initDisplayArea();
        initButtons();
        initFrame();
    }

    private void initFrame() {
        setSize(900, 900);
        setVisible(true);
        setResizable(false);
        setForeground(Color.MAGENTA);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    private void initButtons() {
        ActionListener insert = new Desktop.InsertAction();
        ActionListener command = new Desktop.CommandAction();
        addButton("Back", 0, 1, 2, 1, insert);
        addButton("清零", 2, 1, 2, 1, insert);
        addButton("7", 0, 2, 1, 1, insert);
        addButton("8", 1, 2, 1, 1, insert);
        addButton("9", 2, 2, 1, 1, insert);
        addButton("+", 3, 2, 1, 1, command);
        addButton("4", 0, 3, 1, 1, insert);
        addButton("5", 1, 3, 1, 1, insert);
        addButton("6", 2, 3, 1, 1, insert);
        addButton("-", 3, 3, 1, 1, command);
        addButton("1", 0, 4, 1, 1, insert);
        addButton("2", 1, 4, 1, 1, insert);
        addButton("3", 2, 4, 1, 1, insert);
        addButton("*", 3, 4, 1, 1, command);
        addButton("0", 0, 5, 1, 1, insert);
        addButton("-", 1, 5, 1, 1, insert);
        addButton(".", 2, 5, 1, 1, insert);
        addButton("/", 3, 5, 1, 1, command);
        addButton("=", 0, 6, 4, 1, command);
    }

    private void initDisplayArea() {
        displayField = new JTextField(20);
        displayField.setHorizontalAlignment(4);
        displayField.setBackground(Color.gray);
        displayField.setDisabledTextColor(Color.MAGENTA);
        displayField.setEnabled(false);
        displayField.setFont(new Font("宋体", Font.BOLD, 50));
        gridBagConstraints.gridx = 0;
        gridBagConstraints.gridy = 0;
        gridBagConstraints.gridwidth = 4;
        gridBagConstraints.gridheight = 1;
        gridBagConstraints.fill = 1;
        gridBagConstraints.weightx = 1;
        gridBagConstraints.weighty = 1;
        gridBagLayout.setConstraints(displayField, gridBagConstraints);
        container.add(displayField);
    }

    private void addButton(String label, int column, int row, int with, int height, ActionListener listener) {
        JButton button = new JButton(label);
        button.setForeground(Color.MAGENTA);
        button.setFont(new Font("楷体", Font.BOLD, 36));
        button.addActionListener(listener);
        gridBagConstraints.gridx = column;
        gridBagConstraints.gridy = row;
        gridBagConstraints.gridwidth = with;
        gridBagConstraints.gridheight = height;
        gridBagConstraints.fill = GridBagConstraints.BOTH;
        gridBagConstraints.insets = new Insets(1, 1, 1, 1);
        gridBagLayout.setConstraints(button, gridBagConstraints);
        container.add(button);
    }

    public void calculate(double x) {
        if (this.lastCommand.equals("+")) {
            this.result += x;
        } else if (this.lastCommand.equals("-")) {
            this.result -= x;
        } else if (this.lastCommand.equals("*")) {
            this.result *= x;
        } else if (this.lastCommand.equals("/")) {
            this.result /= x;
        } else if (this.lastCommand.equals("=")) {
            this.result = x;
        }

        this.displayField.setText("" + this.result);
    }

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

    private class CommandAction implements ActionListener {
        private CommandAction() {
        }

        public void actionPerformed(ActionEvent evt) {
            String command = evt.getActionCommand();
            if (Desktop.this.start) {
                Desktop.this.lastCommand = command;
            } else {
                Desktop.this.calculate(Double.parseDouble(Desktop.this.displayField.getText()));
                Desktop.this.lastCommand = command;
                Desktop.this.start = true;
            }
        }
    }

    private class InsertAction implements ActionListener {
        private InsertAction() {
        }

        public void actionPerformed(ActionEvent event) {
            String input = event.getActionCommand();
            if (Desktop.this.start) {
                Desktop.this.displayField.setText("");
                Desktop.this.start = false;
                if (input.equals("-")) {
                    Desktop.this.displayField.setText(Desktop.this.displayField.getText() + "-");
                }
            }

            if (!input.equals("-")) {
                if (input.equals("Back")) {
                    String str = Desktop.this.displayField.getText();
                    if (str.length() > 0) {
                        Desktop.this.displayField.setText(str.substring(0, str.length() - 1));
                    }
                } else if (input.equals("清零")) {
                    Desktop.this.displayField.setText("0");
                    result = 0.0d;
                    Desktop.this.start = true;
                } else {
                    if (input.equals(".")) {
                        if (Desktop.this.displayField.getText().trim().indexOf(".") == -1) {
                            Desktop.this.displayField.setText(Desktop.this.displayField.getText() + input);
                        }
                    } else {
                        Desktop.this.displayField.setText(Desktop.this.displayField.getText() + input);
                    }
                }
            }

        }
    }
}