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);
  }
}

输出

4+(3*(3-1)+2)/2 = 8.0
4 + (-3 * ( 3 - 1 ) + 2) = 0.0
4.5+(3.2+3)/2 = 7.6
-4.5+(3.2-3)/2 = -4.4
Incorret Expression: 4 +-/ (-3 * ( 3 - 1 ) + 2)
Error: null
Incorret Expression: 4.5+(3.2:3)/2
Error: For input string: "3.2:3"

总结

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