Big talk Data Structure-use a stack to implement simple four arithmetic operations and four arithmetic operations on the Data Structure

Big talk Data Structure-use a stack to implement simple four arithmetic operations and four arithmetic operations on the Data Structure

I recently read "big talk Data Structure". Here is an example of using the stack to implement four arithmetic operations. Now I want to use java to implement this function.

The Code is as follows:

Package com. datastruct; import java. util. arrayList; import java. util. stack; import java. util. regex. matcher; import java. util. regex. pattern; public class StackPractice {private static ArrayList <String> symbolList; static {symbolList = new ArrayList <> (); symbolList. add (SymbolEnum. ADD. getVal (); symbolList. add (SymbolEnum. SUBTRACT. getVal (); symbolList. add (SymbolEnum. MULTIPLY. getVal (); symbolList. add (SymbolEnum. DIVIDE. getVal (); symbolList. add (SymbolEnum. LEFT_BRACKET.getVal (); symbolList. add (SymbolEnum. RIGHT_BRACKET.getVal ();} public static void main (String [] args) {String exp = "9 + (3-1) * 3 + 10/2 "; try {String exp2 = convertExp (exp); System. out. println (cal (exp2);} catch (Exception e) {System. out. println (e. getMessage () ;}} private static boolean isNumeric (String str) {Pattern pattern = Pattern. compile ("[0-9] *" ); Matcher isNum = pattern. matcher (str); if (! IsNum. matches () {return false;} return true;}/*** calculates the suffix expression value * @ return */private static int cal (String exp) {String [] expArr = exp. split (""); Stack <String> calStack = new Stack <String> (); for (int I = 0; I <expArr. length; I ++) {String tmp = expArr [I]; if (isNumeric (tmp) {// number into the stack calStack. push (tmp);} else {int num1 = Integer. parseInt (calStack. pop (); // The 1int num2 = Integer is displayed on the top of the stack. parseInt (calStack. pop (); // 2 swit pops up on the top of the stack Ch (tmp) {case "-": calStack. push (num2-num1 + ""); break; case "+": calStack. push (num2 + num1 + ""); break; case "*": calStack. push (num2 * num1 + ""); break; case "/": calStack. push (num2/num1 + ""); break; default: break ;}} return Integer. parseInt (calStack. pop ();}/*** convert the infix expression to the suffix expression * @ return */private static String convertExp (String exp) throws Exception {// convert string to array char [] expArr = exp. toCharArray (); StringBuf Fer sb = new StringBuffer (); Stack <String> symbolStack = new Stack <> (); boolean isLastCharNumberFlag = true; for (int I = 0; I <expArr. length; I ++) {char curChar = expArr [I]; // if a number is added, if it is a symbol, it is placed into the stack for calculation if (Character. isDigit (curChar) {if (isLastCharNumberFlag) {sb. append (curChar);} else {sb. append (""). append (curChar);} isLastCharNumberFlag = true;} else if (symbolList. contains (String. valueOf (curChar) {// symbol // String symbol = String. valueOf (curChar); if (SymbolEnum. RIGHT_BRACKET.getVal (). equals (symbol) {// if it is a right brace, you must match the left brace String symbolStr = symbolStack. pop (); while (! SymbolEnum. LEFT_BRACKET.getVal (). equals (symbolStr) {sb. append (""). append (symbolStr); symbolStr = symbolStack. pop ();} isLastCharNumberFlag = false; continue;} else if (SymbolEnum. DIVIDE. getVal (). equals (symbol) | SymbolEnum. MULTIPLY. getVal (). equals (symbol) {} else {if (symbolStack. isEmpty () {symbolStack. push (symbol); continue;} String symbolStr = symbolStack. peek (); if (SymbolEnum. DIVIDE. getVal (). equals (symbolS Tr) | SymbolEnum. MULTIPLY. getVal (). equals (symbolStr) {while (! SymbolStack. isEmpty () {sb. append (""). append (symbolStack. pop ();} symbolStack. push (symbol); isLastCharNumberFlag = false; continue ;}} symbolStack. push (symbol); isLastCharNumberFlag = false ;}} while (! SymbolStack. isEmpty () {sb. append (""). append (symbolStack. pop ();} return sb. toString ();}/*** operator enumeration * @ author Administrator **/enum SymbolEnum {ADD ("+"), SUBTRACT ("-"), MULTIPLY ("*"), DIVIDE ("/"), LEFT_BRACKET ("("), RIGHT_BRACKET (")"); private String val; public String getVal () {return val;} private SymbolEnum (String val) {this. val = val ;}}}

The program has some bugs for the time being. For example, the expression validity is not verified and multiple parentheses cannot be entered.