JAVA数据结构解析数学表达式

JAVA用栈解析数学表达式(如4*(7+4)):

// brackets.java
// stacks used to check matching brackets
// to run this program: C>java bracketsApp
import java.io.*;                 // for I/O
////////////////////////////////////////////////////////////////
class StackX
   {
   private int maxSize;
   private char[] stackArray;
   private int top;
//--------------------------------------------------------------
   public StackX(int s)       // constructor
      {
      maxSize = s;
      stackArray = new char[maxSize];
      top = -1;
      }
//--------------------------------------------------------------
   public void push(char j)  // put item on top of stack
      {
      stackArray[++top] = j;
      }
//--------------------------------------------------------------
   public char pop()         // take item from top of stack
      {
      return stackArray[top--];
      }
//--------------------------------------------------------------
   public char peek()        // peek at top of stack
      {
      return stackArray[top];
      }
//--------------------------------------------------------------
   public boolean isEmpty()    // true if stack is empty
      {
      return (top == -1);
      }
//--------------------------------------------------------------
   }  // end class StackX
////////////////////////////////////////////////////////////////
class BracketChecker
   {
   private String input;                   // input string
//--------------------------------------------------------------
   public BracketChecker(String in)        // constructor
      { input = in; }
//--------------------------------------------------------------
   public void check()
      {
      int stackSize = input.length();      // get max stack size
      StackX theStack = new StackX(stackSize);  // make stack

      for(int j=0; j<input.length(); j++)  // get chars in turn
         {
         char ch = input.charAt(j);        // get char
         switch(ch)
            {
            case '{':                      // opening symbols
            case '[':
            case '(':
               theStack.push(ch);          // push them
               break;

            case '}':                      // closing symbols
            case ']':
            case ')':
               if( !theStack.isEmpty() )   // if stack not empty,
                  {
                  char chx = theStack.pop();  // pop and check
                  if( (ch=='}' && chx!='{') ||
                      (ch==']' && chx!='[') ||
                      (ch==')' && chx!='(') )
                     System.out.println("Error: "+ch+" at "+j);
                  }
               else                        // prematurely empty
                  System.out.println("Error: "+ch+" at "+j);
               break;
            default:    // no action on other characters
               break;
            }  // end switch
         }  // end for
      // at this point, all characters have been processed
      if( !theStack.isEmpty() )
         System.out.println("Error: missing right delimiter");
      }  // end check()
//--------------------------------------------------------------
   }  // end class BracketChecker
////////////////////////////////////////////////////////////////
class BracketsApp
   {
   public static void main(String[] args) throws IOException
      {
      String input;
      while(true)
         {
         System.out.print(
                      "Enter string containing delimiters: ");
         System.out.flush();
         input = getString();     // read a string from kbd
         if( input.equals("") )   // quit if [Enter]
            break;
                                  // make a BracketChecker
         BracketChecker theChecker = new BracketChecker(input);
         theChecker.check();      // check brackets
         }  // end while
      }  // end main()
//--------------------------------------------------------------
   public static String getString() throws IOException
      {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
      }
//--------------------------------------------------------------
   }  // end class BracketsApp
////////////////////////////////////////////////////////////////