2Write a calculator program with 00 lines of Java code

found a calculator mini program I wrote in college, with a graphical interface that can graphically display the expression syntax tree, hahaha;)

Only200 lines of Java code, not only can calculate addition, subtraction, multiplication, and division, but also can match parentheses~

Code Review:

From the simple interface color matching to the easy-to-understand error prompts, it fully reflects the design philosophy of 'user experience' first; the code exception handling is comprehensive and reasonable, without any loopholes, the code indentation is elegant and generous, and the variable naming is intuitive and easy to understand; combined with moderate-length and clear comments, the program gives a refreshing and elegant feeling. Behind it, it is not difficult to see the author's love for learning and the strict pursuit of design, a glimpse of the craftsmanship spirit, which can truly be said to be a model of applying university data structure knowledge in practice!

The implementation code is shown as follows:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.TextField;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.Stack;
import javax.swing.JFrame;
/** * This is a graphical interface calculator program, which can only perform addition, subtraction, multiplication, and division, * Parentheses are allowed in the expression. Numbers can be decimal numbers */
public class CalcGUI extends JFrame {
  private static final long serialVersionUID = 1L;
  private TreeNode resultTree;
  private String textFieldString;
  private boolean calcSuccess = true;
  private char[][] ops = {
      {'>', '>', '<', '<', '<', '>', '>'},
      {'>', '>', '<', '<', '<', '>', '>'},
      {'>', '>', '>', '>', '<', '>', '>'},
      {'>', '>', '>', '>', '<', '>', '>'},
      {'<', '<', '<', '<', '<', '=', 'E'},
      {'E', 'E', 'E', 'E', 'E', 'E', 'E'},
      {'<', '<', '<', '<', '<', 'E', '='},
  };
  Stack<TreeNode> nodesStack = new Stack<TreeNode>();
  Stack<Character> opsStack = new Stack<Character>();
  public static void main(String[] args) {
    CalcGUI gui = new CalcGUI();
    gui.userGUI();
  }
  public void userGUI() {
    this.setLayout(new BorderLayout());
    TextField tf = new TextField("Please enter the expression, press Enter to start calculation~", 4, 0);
    tf.selectAll();
    tf.getText();
    tf.addKeyListener(new KeyAdapter(){
      public void keyPressed(KeyEvent e){
        if(e.getKeyCode() == KeyEvent.VK_ENTER){
          textFieldString = ((TextField)e.getComponent()).getText();
          calcSuccess = true;
          resultTree = null;
          try{
            resultTree = calc(textFieldString + "#\
          }catch(Exception e1){
            calcSuccess = false;
          }
          CalcGUI.this.repaint();
        }
      }
    });
    this.add(tf, BorderLayout.NORTH);
    this.setSize(500, 500);
    this.setTitle("calc GUI");
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.setResizable(true);
    this.setVisible(true);
  }
  private int levelHeight = 60;
  private int diameter = 25;
  public void paint(Graphics g){
    super.paint(g);
    if(calcSuccess){
      if(resultTree != null){
        g.drawString("The calculation result is:", + resultTree.value, 10,} 8, 0);
        int rootBeginX = this.getWidth() / 2;
        int rootBeginY = 100;
        Point p = new Point(rootBeginX, rootBeginY);
        drawTree(g, resultTree, p, this.getWidth()) / 2 - 20, p);
      }
    }
      g.setColor(Color.RED);
      g.drawString("The expression syntax is incorrect!", 10,} 8, 0);
    }
  }
  private void drawCircle(Graphics g, Point p, int r){
    g.drawOval(p.x - r, p.y - r, r * 2, r * 2);
  }
  private void drawTree(Graphics g, TreeNode node, Point pme, int width, Point pfather){
    if(node == null) return;
//   System.out.println("in drawTree, node.value=" + node.value + ",node.op=" + node.op);
    g.setColor(Color.GREEN);
    this.drawCircle(g, pme, diameter / 2);
    g.drawLine(pme.x, pme.y, pfather.x, pfather.y);
    if(node.op != 'E'){
      g.setColor(Color.BLACK);
      g.drawString(String.valueOf(node.op), pme.x, pme.y);
    }
      g.setColor(Color.BLACK);
      g.drawString(String.valueOf(node.value), pme.x - diameter / 2, pme.y);
    }
    drawTree(g, node.lft, new Point(pme.x - width / 2, pme.y + , levelHeight, width / 2, pme);
    drawTree(g, node.rt, new Point(pme.x + width / 2, pme.y + , levelHeight, width / 2, pme);
  }
  public TreeNode calc(String inStr) throws Exception{
    opsStack.push('#');
    StringBuilder buf = new StringBuilder();
    int i = 0;
    while(i < inStr.length()){
      if(Character.isDigit(inStr.charAt(i)) || inStr.charAt(i) == '.'){// number
        buf.delete(0, buf.length());
        while(i < inStr.length() && 
            (Character.isDigit(inStr.charAt(i)) || inStr.charAt(i) == '.'))
          buf.append(inStr.charAt(i))++));
        Double number = Double.parseDouble(buf.toString());
        nodesStack.push(new TreeNode(number));
      }
        i++;
        continue;
      }// operation
        char op = inStr.charAt(i);
        int subNew = getSub(op);
        boolean goOn = true;
        while(goOn){
          if(opsStack.isEmpty())
            throw new Exception("Too few operators!");
          char opFormer = opsStack.peek();
          int subFormer = getSub(opFormer);
          switch(ops[subFormer][subNew]){
          case '=':
            goOn = false;
            opsStack.pop();
            break;
          case '<':
            goOn = false;
            opsStack.push(op);
            break;
          case '>':
            goOn = true;
            TreeNode n1 = nodesStack.pop();
            TreeNode n0 = nodesStack.pop();
            double rs = doOperate(n0.value, n1.value, opFormer);
            nodesStack.push(new TreeNode(rs, opFormer, n0, n1));
            opsStack.pop();
            break;
          default:
            throw new Exception("No matching operator:"); + op);
          }
        }
        i++;
      }
    }
    return nodesStack.pop();
  }
  private double doOperate(double n0, double n1, char op) throws Exception{
    switch(op){
    case '"}}+: return n0 + n1;
    case '"}}-: return n0 - n1;
    case '"}}*: return n0 * n1;
    case '"}}/: return n0 / n1;
    default: throw new Exception("Illegal operator: "); + op);
    }
  }
  private int getSub(char c){
    switch(c){
      case '"}}+: return 0;
      case '"}}-': return 1;
      case '"}}*': return 2;
      case '"}}/': return 3;
      case '(': return 4;
      case ')': return 5;
      case '#': return 6;
      default : return -1;
    }
  }
}
class TreeNode{
  public double value;
  public char op = 'E';
  public TreeNode lft;
  public TreeNode rt;
  public TreeNode(double value){
    this.value = value;
  }
  public TreeNode(double value, char op, TreeNode lft, TreeNode rt){
    this.value = value;
    this.op = op;
    this.lft = lft;
    this.rt = rt;
  }
  StringBuilder buf = new StringBuilder();
  public String toString(){
    out(this);
    return buf.toString();
  }
  private void out(TreeNode node){
    if(node == null) return;
    out(node.lft);
    if(node.op != 'E')
      buf.append(node.op);
    else
      buf.append(node.value);
    out(node.rt);
  }
}

Summary

The above is what the editor has introduced to everyone2Here is a Java program that writes 00 lines of code to create a calculator, I hope it will be helpful to everyone. If you have any questions, please leave a message, and the editor will reply to everyone in time. I also want to express my sincere gratitude to everyone for supporting the呐喊 tutorial!