简单的字符串运算

package com.feiyang.arithmetic;

import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author Qingtao.Xie
 * @date Feb 23, 2010
 */
public class PostFixExpression
{

  private String str;

  PostFixExpression(String str)
  {
    this.str = str;
  }

  public float result()
  {
    Stack<String> numbers = new Stack<String>();
    numbers.push(null);

    this.str = covertPostEx();
    String[] splitStr = this.str.split(" ");

    for (int i = 0; i < splitStr.length; i++)
    {
      if (isNumber(splitStr[i]))
      {
        numbers.push(splitStr[i]);
      }
      else
      {
        float f1 = Float.parseFloat(numbers.pop());
        float f2 = Float.parseFloat(numbers.pop());
        numbers.push(String.valueOf(calculate(f2, f1, splitStr[i].charAt(0))));
      }
    }

    return Float.parseFloat(numbers.pop());
  }

  public String covertPostEx()
  {
    String postEx = "";
    Stack<String> ops = new Stack<String>();
    ops.push(null);

    int i = 0;
    while (i < this.str.length())
    {
      StringBuffer tmp = new StringBuffer();
      if (isNumber(String.valueOf(str.charAt(i))))
      {
        do
        {
          tmp.append(str.charAt(i));
          i++;
        }
        while (i < this.str.length() && isNumber(String.valueOf(str.charAt(i))));
        postEx += tmp.toString();
        postEx += " ";
      }
      else
      {
        String top = ops.peek();
        if (top != null)
        {
          if (isHigh(top.charAt(0), str.charAt(i)))
          {
            postEx += ops.pop();
            postEx += " ";
          }
          else
          {
            ops.push(String.valueOf(str.charAt(i)));
            i++;
          }
        }
        else
        {
          ops.push(String.valueOf(str.charAt(i)));
          i++;
        }
      }

    }

    while (null != ops.peek())
    {
      postEx += ops.pop();
      postEx += " ";
    }

    System.out.println(this.str + " postFix=" + postEx);

    return postEx;
  }

  boolean isHigh(int first, int second)
  {
    boolean ret = true;

    if ((Operators.MINUS.getOp() == first || Operators.PLUS.getOp() == first)
        && (Operators.MUTIPLY.getOp() == second || Operators.DIV.getOp() == second))
    {
      ret = false;
    }

    return ret;

  }

  boolean isNumber(String num)
  {
    Pattern p = Pattern.compile("//d*");
    Matcher m = p.matcher(num);
    return m.matches();
  }

  float calculate(float a, float b, char op)
  {
    switch (op)
    {
      case '+':
        return a + b;
      case '-':
        return a - b;
      case '*':
        return a * b;
      case '/':
        return a / b;
    }
    return -1;
  }

  /**
   * @param args
   */
  public static void main(String[] args)
  {
    String str = "645-90/4+89/25*3-8";
    PostFixExpression post = new PostFixExpression(str);
    System.out.println(str + "=" + post.result());
  }

}

 

 

 

 

 

package com.feiyang.arithmetic;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author Qingtao.Xie
 * @date Feb 23, 2010
 */
public class StackExpression
{

  private String str;

  private Stack<String> operators = new Stack<String>();

  private Stack<String> numerics = new Stack<String>();

  public StackExpression(String str)
  {
    this.str = str;
  }

  public float result()
  {
    Object[] nums = splitStr("[+|//-|*|/]");
    Object[] ops = splitStr("//d");
    String[] dividedStr = new String[nums.length + ops.length];
    //compsite the string to an array
    for (int i = 0, j = 0; j < nums.length; i++, j++)
    {
      dividedStr[i] = (String) nums[j];
      if (j < ops.length)
      {
        i = i + 1;
        dividedStr[i] = (String) ops[j];
      }
    }

    operators.push(null);

    for (int k = 0; k < dividedStr.length;)
    {
      if (isNumber(dividedStr[k]))
      {
        numerics.push(dividedStr[k]);
        k++;
        System.out.println("------number:" + numerics.toString());
      }
      else
      {
        String top = operators.peek();
        if (null != top
            && isHigh(operators.peek().charAt(0), dividedStr[k].charAt(0)))
        {
          float f2 = Float.parseFloat(numerics.pop());
          float f1 = Float.parseFloat(numerics.pop());
          char op = operators.pop().charAt(0);
          numerics.push(String.valueOf(calculate(f1, f2, op)));
        }
        else
        {
          operators.push(dividedStr[k]);
          k++;
        }
        System.out.println("------op:" + operators.toString());
      }
    }

    while (operators.peek() != null)
    {
      float f2 = Float.parseFloat(numerics.pop());
      float f1 = Float.parseFloat(numerics.pop());
      char op = operators.pop().charAt(0);
      numerics.push(String.valueOf(calculate(f1, f2, op)));
      System.out.println("------number:" + numerics.toString());
      System.out.println("------op:" + operators.toString());
    }

    return Float.parseFloat(numerics.peek());
  }

  private Object[] splitStr(String pattern)
  {
    Pattern p = Pattern.compile(pattern);
    String[] strsWithEmpty = p.split(this.str);
    List<String> list = new ArrayList<String>();

    for (int i = 0; i < strsWithEmpty.length; i++)
    {
      if (strsWithEmpty[i].length() != 0)
      {
        list.add(strsWithEmpty[i]);
      }
    }
    return list.toArray();
  }

  boolean isNumber(String num)
  {
    Pattern p = Pattern.compile("//d*");
    Matcher m = p.matcher(num);
    return m.matches();
  }

  boolean isHigh(int first, int second)
  {
    boolean ret = true;

    if ((Operators.MINUS.getOp() == first || Operators.PLUS.getOp() == first)
        && (Operators.MUTIPLY.getOp() == second || Operators.DIV.getOp() == second))
    {
      ret = false;
    }

    return ret;

  }

  float calculate(float a, float b, char op)
  {
    switch (op)
    {
      case '+':
        return a + b;
      case '-':
        return a - b;
      case '*':
        return a * b;
      case '/':
        return a / b;
    }
    return -1;
  }

  /**
   * @param args
   */
  public static void main(String[] args)
  {
    // TODO Auto-generated method stub
    String str = "645-90/4+89/25*3-8";
    StackExpression c = new StackExpression(str);
    System.out.println(str + "=" + c.result());

  }

}