Question

2.) Postfix to infix translator (NOTE: This is NOT the evaluator you have already coded!) • Create a java class called PostfixToInfixTranslator that includes a main method. • The code you write should prompt the user for an expression in postfix notation and use ArrayStack to output the equivalent expression in infix. • See the following session: Enter a postfix expression: 3 4 + 2 * In infix notation that is: ((3+4)*2) Translate another expression [y/n]? y Enter a postfix expression: 4 2 + 3 5 1 - * + In infix notation that is: ((4+2)+(3*(5-1))) Translate another expression [y/n]? n • NOTE: The postfix expression has to accept spaces, double digit numbers, and negative numbers. So .charAt() is not a good approach. Maybe a scanner on a string?

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StackADT, EmptyCollectionException, and ArrayStack code already below, please use these.

public interface StackADT<T> //Provide layout of what we want something to do w/o supplying the way it gets done = interface
{
   public void push( T element) ;
  
   public T pop () throws EmptyCollectionException;
  
   public T peek() throws EmptyCollectionException;
  
   public boolean isEmpty();
  
   public int size();
}

public class EmptyCollectionException extends Exception
{
  
   private static final long serialVersionUID = 358083002087971606L;

   public EmptyCollectionException()
   {
       super();
   }
  
   public EmptyCollectionException(String msg)
   {
       super(msg);
   }
}

import java.util.Arrays;

public class ArrayStack<T> implements StackADT<T> //We agree to supply all functions that we say exist StackADT Functions correlate to ArrayStack
{
   private final static int DEFAULT_CAPACITY = 100;
   private int top;
   private T[] stack;
  
   public ArrayStack()
   {
       this(DEFAULT_CAPACITY);
   }
  
   @SuppressWarnings("unchecked")
   public ArrayStack(int initialCapacity)
   {
       top = 0;
       stack = (T[]) new Object [initialCapacity]; //Have to cast Object Array to T array in order for placeholder to work. Java just works like that.
   }
  
   public void push( T element)
   {
       if(size() == stack.length)
           expandCapacity();
       stack [top] = element;
       ++top;
   }
  
   public T pop() throws EmptyCollectionException
   {
       if(isEmpty())
           throw new EmptyCollectionException();
       --top;
       T result = stack[top];
       stack [top] = null; // Top before that ends up being empty; Makes it clean
       return result;
   }
  
   public T peek() throws EmptyCollectionException
   {
       if(isEmpty())
           throw new EmptyCollectionException();
       return stack[top -1];
   }
  
   public int size()
   {
       return top;
   }
  
   public boolean isEmpty()
   {
       // Even shorter
       return top ==0;
       // Short
//       boolean a = top == 0;
//       return a;
       // long way
//       if(top==0)
//           return true;
//       else
//           return false;
   }
  
   public void expandCapacity()
   {
       stack = Arrays.copyOf(stack, stack.length * 2); //Would values stay the same but only place in memory changes? Hexa decimal #'s?
   }
  
   public String toString()
   {
       String output = "ArrayStack-> [ ";
       for(int i =top-1; i >=0 ; i--)
       {
           output+= stack[i].toString() + " ";
       }
      
       output+= "]";
       return output;
   }
}

WHAT I ALREADY HAVE CODED IN TRANSLATOR, PLEASE HELP. I don't know how to allow spaces, double digits, and negative numbers, and also how to loop the scanner input.

import java.util.Scanner;
import java.util.Stack;

public class PostfixToInfixTranslator
{

   public static void main(String[] args) throws EmptyCollectionException
   {
       PostfixToInfixTranslator obj = new PostfixToInfixTranslator();
       Scanner sc = new Scanner(System.in);
       System.out.print("Postfix : ");
       String postfix = sc.next();
       System.out.println("Infix : " +obj.convert(postfix));
      

   }

   private boolean isOperator(char c)
   {
       if(c == '+' || c== '-' || c== '*' || c=='/' || c=='^')
           return true;
       return false;
   }
  
   public String convert(String postfix) throws EmptyCollectionException
   {
       ArrayStack<String> s = new ArrayStack<>();
      
       for(int i =0; i < postfix.length(); i++)
       {
           char c = postfix.charAt(i);
           if(isOperator(c))
           {
               String b = s.pop();
               String a = s.pop();
               s.push("("+a+c+b+")");
           }
           else
               s.push(""+c);
       }
       return s.pop();
   }

}

Answer 1

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

public class PostfixToInfixTranslator {

    public static void main(String[] args) throws EmptyCollectionException {
        PostfixToInfixTranslator obj = new PostfixToInfixTranslator();
        try {
            BufferedReader input = new BufferedReader(new InputStreamReader(System.in));

            String cmd = "y";
            String[] postfix;
            while (cmd.equalsIgnoreCase("y")) {
                System.out.print("Enter a Postfix expression : ");
                postfix = input.readLine().split(" ");
                System.out.println("Infix Notation is : " + obj.convert(postfix));
                System.out.println("Translate another expression[y/n]?");
                cmd = input.readLine();
            }
        } catch (IOException ex) {
        }


    }

    private boolean isOperator(String c) {
        if (c.equalsIgnoreCase("+") || c.equalsIgnoreCase("-")
                || c.equalsIgnoreCase("*") || c.equalsIgnoreCase("/")
                || c.equalsIgnoreCase("^"))
            return true;
        return false;
    }

    public String convert(String[] postfix) throws EmptyCollectionException {
        ArrayStack<String> s = new ArrayStack<>();

        for (int i = 0; i < postfix.length; i++) {
            String c = postfix[i];

            if (isOperator(c)) {
                String b = s.pop();
                String a = s.pop();
                s.push("(" + a + c + b + ")");
            } else
                s.push(c);
        }
        return s.pop();
    }

}