InfixApp.java

package cn.codepub.algorithms.stack;

import cn.codepub.algorithms.utils.StackX;

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

/**
 * <p>
 * Created with IntelliJ IDEA. 2016/1/8 19:16
 * </p>
 * <p>
 * ClassName:InfixApp
 * </p>
 * <p>
 * Description:中缀表达式转后缀表达式，For Example<br/>
 * Enter infix:<br/>
 * 2+4-4+3*2<br/>
 * Postfix is 24+4-32*+<br/>
 * </P>
 *
 * @author Wang Xu
 * @version V1.0.0
 * @since V1.0.0
 */
public class InfixApp {
    public static void main(String[] args) throws IOException {
        String input, output;
        while (true) {
            System.out.println("Enter infix:");
            System.out.flush();
            input = getString();
            if (input.equals("")) {
                break;
            }
            InToPost theTrans = new InToPost(input);
            output = theTrans.doTrans();
            System.out.println("Postfix is " + output + "\n");
        }

    }

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

}


class InToPost {
    private StackX<Character> theStack;
    private String input;
    private String output = "";

    public InToPost(String in) {
        input = in;
        int stackSize = input.length();
        theStack = new StackX<Character>(stackSize);
    }

    public String doTrans() {
        for (int j = 0; j < input.length(); j++) {
            char ch = input.charAt(j);
            theStack.displayStack("For " + ch + " ");
            switch (ch) {
                case '+':
                case '-':
                    gotOper(ch, 1);
                    break;
                case '*':
                case '/':
                    gotOper(ch, 2);
                    break;
                case '(':
                    theStack.push(ch);
                    break;
                case ')':
                    gotParen(ch);
                    break;
                default:
                    output = output + ch;
                    break;
            }
        }
        while (!theStack.isEmpty()) {
            theStack.displayStack("While ");
            output = output + theStack.pop();
        }
        theStack.displayStack("End ");
        return output;
    }

    public void gotOper(char opThis, int prec1) {
        while (!theStack.isEmpty()) {
            char opTop = theStack.pop();
            if (opTop == '(') {
                theStack.push(opTop);
                break;
            } else {
                int prec2;
                if (opTop == '+' || opTop == '-') {
                    prec2 = 1;
                } else {
                    prec2 = 2;
                }
                if (prec2 < prec1) {
                    theStack.push(opTop);
                    break;
                } else {
                    output = output + opTop;
                }
            }
        }
        theStack.push(opThis);
    }

    public void gotParen(char ch) {
        while (!theStack.isEmpty()) {
            char chx = theStack.pop();
            if (chx == '(') {
                break;
            } else {
                output = output + chx;
            }
        }
    }
}