interpreterdemo.java

《深入浅出设计模式》的完整源代码

package interpreter;

public class InterpreterDemo {
  public static boolean precedence (char a, char b) {
    String high = "*/", low = "+-";
    if (a == '(')
      return false; // if (a == '(' && b == ')') return false;
    if (a == ')' && b == '(') {
      System.out.println (")-(");
      return false;
    }
    if (b == '(')
      return false;
    if (b == ')')
      return true;
    if (high.indexOf (a) > -1 && low.indexOf (b) > -1)
      return true;
    if (high.indexOf (a) > -1 && high.indexOf (b) > -1)
      return true;
    if (low.indexOf (a) > -1 && low.indexOf (b) > -1)
      return true;
    return false;
  }

  public static String convertToPostfix (String in) {
    StkChar opstk = new StkChar ();
    StringBuffer out = new StringBuffer ();
    String opers = "+-*/()";
    char topsym = '+';
    boolean empty;

    for (int i = 0; i < in.length (); i++)
      if (opers.indexOf (in.charAt (i)) == -1)
        out.append (in.charAt (i));
      else {
        while (! (empty = opstk.isEmpty ())
               && precedence (topsym = opstk.pop (), in.charAt (i)))
          out.append (topsym);
        if (!empty)
          opstk.push (topsym);
        if (empty || in.charAt (i) != ')')
          opstk.push (in.charAt (i));
        else
          topsym = opstk.pop ();
      }
    while (!opstk.isEmpty ())
      out.append (opstk.pop ());
    return out.toString ();
  }

  public static int evaluate (String in) {
    StkInt stack = new StkInt ();
    String opers = "+-*/";
    for (int a, b, i = 0; i < in.length (); i++)
      if (opers.indexOf (in.charAt (i)) == -1)
        stack.push (in.charAt (i) - 48);
      else {
        b = stack.pop ();
        a = stack.pop ();
        if (in.charAt (i) == '+')
          a = a + b;
        else if (in.charAt (i) == '-')
          a = a - b;
        else if (in.charAt (i) == '*')
          a = a * b;
        else if (in.charAt (i) == '/')
          a = a / b;
        stack.push (a);
      }
    return stack.pop ();
  }

  public static void main (String[] args) {
    String express="2+3*4-5+6";
    String postfix = convertToPostfix (express);
    System.out.print(express);
    System.out.print (" -- " + postfix);
    System.out.println (" -- " + evaluate (postfix));
  }
}