Ký pháp Ba Lan ngược

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ONP {

    static class Stack{
        //properties
        final int size=100;
        char[]s;
        int top;
        //Constructor
        public Stack()
        {
            s=new char[size];
            top=-1;
        }
        //method
        public boolean isEmpty()
        {
            if(top==-1) return true;
            else return false;
        }
        public void push(char c)
        {
            top+=1;
            s[top]=c;
        }
        public char pop()
        {
            if(!this.isEmpty())
            {
                return s[top--];
            }else {
                System.out.println("Stack underflow");
                return '0';
            }
        }
        public char peek() {
            if(!this.isEmpty()) return s[top];
            else {
                System.out.println("Stack underflow");
                return '1';
            }
        }
    }
    public static int priority(char c)
    {
        if(c=='('||c==')') return 0;
        else if(c=='+'||c=='-') return 1;
        else if(c=='*'||c=='/') return 2;
        else return 3;
    }
    public static void main(String[] args) throws FileNotFoundException {
        System.setIn(new FileInputStream("D:\\SVMC\\kpbl.txt"));
        Scanner sc=new Scanner(System.in);
        byte testCase=sc.nextByte();
        for(int tc=1;tc<=testCase;tc++)
        {
            String strInput=sc.next();
            Stack S=new Stack();
            for(int i=0;i<strInput.length();i++) {
                char tmpt=strInput.charAt(i);
                if(tmpt>=97&&tmpt<=122)
                {
                    System.out.print(tmpt);
                }else {
                    if(tmpt=='(') S.push(tmpt);
                    else
                    {
                        if(tmpt==')')
                        {
                            while(S.peek()!='(')
                            {
                                System.out.print(S.pop());
                            }
                            S.pop();//remove '(' in stack
                        }
                        else
                        {
                            if(priority(S.peek())<=priority(tmpt)) S.push(tmpt);
                            else S.pop();
                        }
                    }
                }
            }
            while(!S.isEmpty())
            {
                System.out.print(S.pop());
            }
            System.out.println();
        }
    }
}