toPostfix

class ToPostfix{


    private Stack theStack;
    private String input;
    private Queue queue;


    public ToPostfix(String in){
        input = in;
        int stackSize = input.length();
        int queueSize = input.length();
        queue = new Queue(queueSize);
        theStack = new Stack(stackSize);
    }


    public String trabslation(){
        for(int j=0; j<input.length(); j++)
        {
            char ch = input.charAt(j);
            switch(ch)
            {
                case '+':
                case '-':
                    operand(ch, 1);
                    break;

                case '*':
                case '/':
                    operand(ch, 2);
                    break;

                case '(':
                    theStack.push(ch);
                    break;

                case ')':
                    parent(ch);
                    break;

                default:
                    queue.enqueue(ch);
                    break;
            }
        }

        while( !theStack.isEmpty()){
            queue.enqueue(theStack.pop());
        }
        return queue.getString();
    }


    public void operand(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
                    queue.enqueue(opTop);
            }
        }
        theStack.push(opThis);
    }


    public void parent(char ch){
        while( !theStack.isEmpty()){
            char chx = theStack.pop();
            if( chx == '(' )
                break;
            else
                queue.enqueue(chx);
        }
    }

}