算术表达式系列之后缀表达式求值

package data.struct.algorithm;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Stackfix2 {
    private int maxSize;
    private int stackArr[];
    private int top;

    public Stackfix2(int maxSize) {
        this.maxSize = maxSize;
        stackArr = new int[maxSize];
        top = -1;
    }

    // 进栈
    public void push(int value) {
        stackArr[++top] = value;
    }

    // 出栈
    public int pop() {
        return stackArr[top--];
    }

    // 显示栈顶元素
    public int peek() {
        return stackArr[top];
    }

    // 判断栈是否为空
    public boolean isEmpty() {
        return top == -1;
    }

    public boolean isFull() {
        return top == maxSize - 1;
    }
}

class Postfix {
    private Stackfix2 theStackfix2;
    private String input;

    public Postfix(String in) {
        input = in;
    }

    public int doCalculate() {
        int num1;
        int num2;
        int inresult;
        char ch;
        int j;
        theStackfix2 = new Stackfix2(20);
        for (j = 0; j < input.length(); j++) {
            ch = input.charAt(j);
            // 如果字符为整数，则进行类型强制转换，并压入栈中
            if (ch >= '0' && ch <= '9') {
                theStackfix2.push((int) (ch - '0'));
            } else {
                // 测试用例最最关键的位置，考虑计算过程中的操作数的位置
                // 先弹出栈的元素是第二个操作数，后弹出栈的是第一个操作数
                num2 = theStackfix2.pop();
                num1 = theStackfix2.pop();
                switch (ch) {
                case '+':
                    inresult = num1 + num2;
                    break;
                case '-':
                    inresult = num1 - num2;
                    break;
                case '*':
                    inresult = num1 * num2;
                    break;
                case '/':
                    inresult = num1 / num2;
                    break;
                default:
                    inresult = 0;
                    break;
                }
                theStackfix2.push(inresult);
            }
        }
        return theStackfix2.pop();
    }
}

public class PostfixValue {

    /**
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {

        while (true) {
            System.out.println("Enter a Postfix:");
            System.out.flush();
            String input;
            int result;
            input = getString();
            Postfix parse = new Postfix(input);
            result = parse.doCalculate();
            System.out.println("Postfix求值的结果是：" + result);
        }
    }

    public static String getString() throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bufr = new BufferedReader(isr);
        return bufr.readLine();
    }

}