I discovered a calculator applet I wrote in college, and there is also a graphical interface that can graphically display expression syntax trees, haha;)
Only 200 lines of Java code can not only calculate addition, subtraction, multiplication and division, but also match brackets~
Code comments:
From simple interface color matching to simple and easy-to-understand error prompts, all reflect the design concept of "user experience" first; code exception handling is comprehensive and reasonable, without leaking, code indentation is elegant and generous, variable naming is intuitive and easy to understand; combined with moderate and simple comments, the overall program gives people a fresh and refined feeling. It is not difficult to see the author's love for learning and his demand for design, which shows the craftsman spirit. It is truly a model for applying data structures in college!
The implementation code is 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;/** * Calculator program for the graphical interface can only calculate addition, subtraction, multiplication and division, and there can be brackets in the equation. numeric can be decimal */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', 'E', 'E'}, {'<', '<', '<', '<', 'E', '='}, }; Stack<TreeNode> nodesStack = new Stack<TreeNode>(); Stack<Character> opsStack = new Stack<Character>(); publicstaticvoidmain(String[] args) { CalcGUI gui = new CalcGUI(); gui.userGUI(); } publicvoiduserGUI(){ this.setLayout(new BorderLayout()); TextField tf = new TextField("Please enter the expression, press Enter to start the calculation~", 40); tf.selectAll(); tf.getText(); tf.addKeyListener(new KeyAdapter(){ publicvoidkeyPressed(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; publicvoidpaint(Graphics g){ super.paint(g); if(calcSuccess){ if(resultTree != null){ g.drawString("calculate the result: " + resultTree.value, 10, 80); int rootBeginX = this.getWidth() / 2; int rootBeginY = 100; Point p = new Point(rootBeginX, rootBeginY); drawTree(g, resultTree, p, this.getWidth() / 2 - 20, p); } }else{ g.setColor(Color.RED); g.drawString("Expression syntax is incorrect!", 10, 80); } } privatevoiddrawCircle(Graphics g, Point p, int r){ g.drawOval(px - r, py - r, r * 2, r * 2); } privatevoiddrawTree(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); }else{ 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); } 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)); }else if(inStr.charAt(i) == ' '){ i++; continue; }else{// operation char op = inStr.charAt(i); int subNew = getSub(op); boolean goOn = true; while(goOn){ if(opsStack.isEmpty()) throw new Exception("There are 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(); } privatedoubledoOperate(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); } } privateintgetSub(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(); } privatevoidout(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); }}Summarize
The above is the 200 lines of Java code introduced by the editor to write a calculator program. I hope it will be helpful to everyone. If you have any questions, please leave me a message and the editor will reply to everyone in time. Thank you very much for your support to Wulin.com!