Java实现四则混合运算代码示例

使用栈来实现，可以处理运算优先级。

使用自然四则运算表达式即可，如：4+(3*(3-1)+2)/2。无需把表达式先转换为逆波兰等形式。

package com.joshua.cal; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Set; import java.util.Stack; public class Calculator {   private final Stack<Double> numStack = new Stack<Double>();   private final Stack<Character> opStack = new Stack<Character>();   private char currentOperator;   private char opStackTop;   private int i;   private String expression;   @SuppressWarnings("rawtypes")   public void exec(String expression) {     try {       clean();       if (expression == null || expression.isEmpty()) {         throw new IllegalArgumentException("Blank Expression!");       }       this.expression = expression;       opStack.push(TERMINATE_TOKENS.START_END_MARK);       List tokens = TOKENIZER.exec(expression           + TERMINATE_TOKENS.START_END_MARK);       for (; i < tokens.size(); i++) {         final Object token = tokens.get(i);         if (token instanceof Double) {           processOperand((double) token);         } else {           processOperator((char) token);         }       }     } catch (Throwable e) {       System.err.println(String.fORMat(           "Incorret Expression: %s\nError: %s", expression,           e.getMessage()));     }   }   private void processOperand(final double operand) {     numStack.push(operand);   }   private void processOperator(final char currentOperator) {     this.currentOperator = currentOperator;     this.opStackTop = opStack.peek();     char calMode = CALCULATE_MODE.getRule(currentOperator, opStackTop);     switch (calMode) {     case '>':       processStackHigerPriorityOperator();       break;     case '<':       processStackLowerPriorityOperator();       break;     case '=':       processStackEqualPriorityOperator();       break;     default:       break;     }   }   private void processStackLowerPriorityOperator() {     opStack.push(currentOperator);   }   private void processStackHigerPriorityOperator() {     numStack.push(CALCULATE.exec(opStack.pop(), numStack.pop(),         numStack.pop()));     --i; // pointer back to the previous operator.   }   private void processStackEqualPriorityOperator() {     if (TERMINATE_TOKENS.START_END_MARK == currentOperator) {       System.out.println(expression + " = " + numStack.peek());     } else if (')' == currentOperator) {       opStack.pop();     }   }   public void clean() {     numStack.clear();     opStack.clear();     i = 0;   }   public static void main(String[] args) {     Calculator cal = new Calculator();     cal.exec("4+(3*(3-1)+2)/2"); // = 8     cal.exec("4 + (-3 * ( 3 - 1 ) + 2)"); // = 0     cal.exec("4 +-/ (-3 * ( 3 - 1 ) + 2)"); // incorrect expression!     cal.exec("4.5+(3.2+3)/2"); // = 7.6     cal.exec("4.5+(3.2:3)/2"); // incorrect expression!     cal.exec("-4.5+(3.2-3)/2"); // = -4.4   } } enum CALCULATE {   INSTANCE;   public static double exec(final char operator, final double right,       final double left) {     switch (operator) {     case '+':       return left + right;     case '-':       return left - right;     case '*':       return left * right;     case '/':       return left / right;     default:       throw new IllegalArgumentException("Unsupported operator: "           + operator);     }   } } enum TERMINATE_TOKENS {   INSTANCE;   public static final char START_END_MARK = '#';   private static final Map<Character, Integer> TOKENs = new HashMap<Character, Integer>();   static {     // token, token id     TOKENs.put('+', 0);     TOKENs.put('-', 1);     TOKENs.put('*', 2);     TOKENs.put('/', 3);     TOKENs.put('(', 4);     TOKENs.put(')', 5);     TOKENs.put(START_END_MARK, 6);   }   private static Set<Character> NEGATIVE_NUM_SENSITIVE = new HashSet<Character>();   public static synchronized Set<Character> getNegativeNumSensitiveToken() {     if (NEGATIVE_NUM_SENSITIVE.size() == 0) {       NEGATIVE_NUM_SENSITIVE.addAll(TOKENs.keySet());       NEGATIVE_NUM_SENSITIVE.remove(')');     }     return NEGATIVE_NUM_SENSITIVE;   }   public static boolean isTerminateToken(final char token) {     Set<Character> keys = TOKENs.keySet();     return keys.contains(token);   }   public static int getTokenId(final char token) {     return TOKENs.get(token) == null ? -1 : TOKENs.get(token);   }   public static int getTokenSize() {     return TOKENs.size();   } } enum CALCULATE_MODE {   INSTANCE;   private static char[][] RULES = {       // + - * / ( ) #       { '>', '>', '<', '<', '<', '>', '>' }, // +       { '>', '>', '<', '<', '<', '>', '>' }, // -       { '>', '>', '>', '>', '<', '>', '>' }, // *       { '>', '>', '>', '>', '<', '>', '>' }, // /       { '<', '<', '<', '<', '<', '=', 'o' }, // (       { '>', '>', '>', '>', 'o', '>', '>' }, // )       { '<', '<', '<', '<', '<', 'o', '=' }, // #   };   static {     if (RULES.length != TERMINATE_TOKENS.getTokenSize() || RULES.length < 1         || RULES[0].length != TERMINATE_TOKENS.getTokenSize()) {       throw new IllegalArgumentException("Rules matrix is incorrect!");     }   }   public static char getRule(final char currentOperator, final char opStackTop) {     try {       return RULES[TERMINATE_TOKENS.getTokenId(opStackTop)][TERMINATE_TOKENS           .getTokenId(currentOperator)];     } catch (Throwable e) {       throw new RuntimeException("No rules were defined for some token!");     }   } } enum TOKENIZER {   INSTANCE;   private static final StringBuilder BUFFER = new StringBuilder();   private static String clearExpression(String expression) {     return expression.replaceAll(" ", "");   }   private static Character PREVIOUS_CHAR;   private static void clean() {     BUFFER.delete(0, BUFFER.length());     PREVIOUS_CHAR = null;   }   private static boolean processNegativeNumbers(final String exp,       final int index) {     char c = exp.charAt(index);     if (('+' == c || '-' == c)         && (PREVIOUS_CHAR == null || TERMINATE_TOKENS             .getNegativeNumSensitiveToken().contains(PREVIOUS_CHAR))         && !TERMINATE_TOKENS.isTerminateToken(exp.charAt(index + 1))) {       BUFFER.append(c);       return true;     }     return false;   }   @SuppressWarnings({ "unchecked", "rawtypes" })   public static List<?> exec(final String expression) {     clean();     String exp = clearExpression(expression);     List result = new LinkedList();     for (int i = 0; i < exp.length(); i++) {       char c = exp.charAt(i);       if (TERMINATE_TOKENS.isTerminateToken(c)) {         if (processNegativeNumbers(exp, i))           continue;         if (BUFFER.length() > 0) {           result.add(Double.valueOf(BUFFER.toString()));           BUFFER.delete(0, BUFFER.length());         }         result.add(c);       } else {         BUFFER.append(c);       }       PREVIOUS_CHAR = c;     }     return Collections.unmodifiableList(result);   } }