java - 简单逻辑的计算器问题

Question

我是 Java 新手，我给自己设定的任务是尝试创建一个简单的计算器(和 GUI)，以提高我对该语言的理解和技能。

获取此代码:

import java.awt.FlowLayout;
import java.io.*;
import java.awt.*;
import java.awt.event.*; 

import javax.swing.*;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;


public class calc extends JFrame {


    public JTextField input;
    public JTextField output;
    public JPanel Window;
    public JButton math_button[] = new JButton[5];
    public JButton number_button[] = new JButton[10];
    public String[] number_button_name = {"1","2","3","4","5","6","7","8","9","0"};
    public String[] name = {"Add", "Mulitply", "Divide", "Subtract", "Equals"};
    public JFrame frame = new JFrame(); 
    public JPanel math_panel = new JPanel();
    public JPanel number_panel = new JPanel();
    public JTextField math_input = new JTextField();
    boolean trrgger = false;

    thehandler handler = new thehandler();

    public void go()
    {

        for(int b=0; b<number_button.length; b++)
        {
            number_button[b] = new JButton(number_button_name[b]);
            number_button[b].addActionListener(handler);
            number_panel.add(number_button[b]);

        }

        for(int i=0; i<math_button.length;i++)
        {
            math_button[i] = new JButton(name[i]);
            math_button[i].addActionListener(handler);
            math_panel.add(math_button[i]);

        }


        frame.getContentPane().add(BorderLayout.NORTH, math_input);
        frame.getContentPane().add(BorderLayout.SOUTH, math_panel);
        frame.getContentPane().add(BorderLayout.CENTER, number_panel);
        frame.setSize(400,400);
        frame.setVisible(true);



    }

    //Method to handle the math and return the results of whichever 'button' was pressed
    static int Math(String button_num, int first_num, int second_num)
    {
        int total = 0;
        if(button_num == "Add")
        {
            total = first_num + second_num;
        }

        else if (button_num == "Mulitply") //multiply
        {
            total = first_num * second_num;
        }

        else if (button_num == "Divide") //divide
        {
            total = first_num / second_num;
        }

        else if (button_num == "Substract") //subtract
        {
            total = first_num - second_num;
        }

        else if (button_num == "Equals") //subtract
        {
            total = total;
        }

        return total;
    }

    //Action Events - Code that is triggered once the associated button is clicked


    public class thehandler implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {


            for (int h = 0; h <math_button.length; h++)
            {
                if(event.getSource()==math_button[h])
                {
                    int firstn = Integer.parseInt(math_input.getText());
                    math_input.setText("");
                    int secondn = Integer.parseInt(math_input.getText());

                    System.out.println(calc.Math(math_button[h].getText(), firstn, secondn));

                }

            }

            for(int n=0; n<number_button.length; n++)
            {
                if(event.getSource()==number_button[n])
                {
                    String number_clicked = (number_button[n].getText());
                    String number = math_input.getText();
                    math_input.setText(number + number_clicked);

                }



            }

        }       
    }

}

此代码背后的想法是创建一个简单的 GUI，并允许用户输入所需数量的数字，然后按“等于”按钮显示结果。然而，正如我所说，我的逻辑有问题。我可以从 JTextField 获取第一个输入的数字，在第一个变量初始化后清除文本，但这就是程序崩溃的地方。变量“second_num”作为空白传递给“Math”方法(这会引发错误)，因为这就是我告诉 ActionEvent 要做的事情，以便更流畅地使用程序，没有用户希望必须继续清除使用计算器时的输入框。

有人有什么想法吗？

谢谢

Answer 1

int firstn = Integer.parseInt(math_input.getText());
math_input.setText("");
int secondn = Integer.parseInt(math_input.getText());

您究竟希望上述几行代码做什么？您将从 math_input 获取文本。然后将其设置为空字符串。通过立即取回字符串，您希望得到除空字符串之外的其他内容？

正确的做法是:

• 第一次调用处理程序(即单击“数学”按钮)时收集输入。将其存储在某个地方。
• 下次调用此处理程序时，您将获得下一个输入。依此类推，直到用户单击“=”来计算整个表达式。

建议:如果您是 java 新手，您可能会发现首先在命令行上创建计算器更容易。计算器的功能不需要 GUI。在命令行中收集输入更加简单。如果您成功了，那么您可以继续使用 Swing 等更奇特的东西