原文出处:
CarpenterLee
发现了大学时候写的计算器小程序,还有个图形界面,能够图形化展示表达式语法树,哈哈;)
只有200行Java代码,不但能够计算加减乘除,还能够匹配小括号~
代码点评:
从朴素的界面配色到简单易懂错误提示,无不体现了“用户体验”至上的设计理念;代码异常处理全面合理、滴水不漏,代码缩进优雅大方,变量命名直观易懂;再结合长度适中简单明了的注释,程序整体给人一种清新脱俗之感。背后不难看出作者对学习的热爱以及对设计的苛求,工匠精神可见一斑,真可谓是大学数据结构学以致用的典范!
关于数据结构的干货,可参考博主的《深入理解Java集合框架》系列文章,一定不让你失望。
实现算法参考严蔚敏的《数据结构(C语言版)》第三章“栈和队列”,3.2.5节“表达式求值”。
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; /** * 图形界面的计算器程序,只能计算加减乘除, * 算式中可以有小括号。数字可以是小数 */ 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("请输入表达式,按Enter开始计算~", 40); 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("计算结果为:" + 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("表达式语法有误!", 10, 80); } } 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); }