Question

● For this task you are required to refactor the badly written program RPN.java. This program is a Reverse-Polish Notation calculator which uses a stack.

● You should also fix the indentation of the code.

I AM USING ECLIPSE. THANK YOU IN ADVANCE

import java.util.Scanner;

public class StackNode {
   public StackNode(double data, StackNode underneath) {
       this.data = data;
       this.underneath = underneath;
}
   public StackNode underneath;
  
   public double data;
}

public class RPN {
  
   public void into(double new_data) {
       StackNode new_node = new StackNode(new_data, top);
       top = new_node;
   }
  
   public double outof( ) {
      
       double top_data = top.data;
       top = top.underneath;
       return top_data;
   }
      
   public RPN(String command) {
       top = null;
       this.command = command;
           }
      
   public double get( ) {
       double a, b;
       int j;
          
       for(int i = 0; i < command.length( ); i++) {
           if(Character.isDigit(command.charAt(i))) {// if it's a digit
               double number;
              
       String temp = "";// get a string of the number
      
       for(j = 0; (j < 100) && (Character.isDigit(command.charAt(i)) || (command.charAt(i) == '.')); j++, i++) {
          
           temp = temp + String.valueOf(command.charAt(i));
       }
// convert to double and add to the stack
       number = Double.parseDouble(temp);
  
       into(number);
       }else if(command.charAt(i) == '+') {
           b = outof( );
           a = outof( );
           into(a + b);
       }else if(command.charAt(i) == '-') {
           b = outof( );
           a = outof( );
           into(a - b);
       }else if(command.charAt(i) == '*') {
           b = outof( );
           a = outof( );
           into(a * b);
       }else if(command.charAt(i) == '/') {
           b = outof( );
           a = outof( );
           into(a / b);
       }else if(command.charAt(i) == '^') {
           b = outof( );
           a = outof( );
           into(Math.pow(a, b));
       }else if(command.charAt(i) != ' ') {
           throw new IllegalArgumentException( );
       }
       }

       double val = outof( );

       if(top != null) {
           throw new IllegalArgumentException( );
       }

       return val;
       }

   private String command;
   private StackNode top;

   public static void main(String args[]) {/* main method */
       while(true) {
           Scanner in = new Scanner(System.in);
           System.out.println("Enter RPN expression or \"quit\".");
           String line = in.nextLine( );
       if(line.equals("quit")) {
           break;
       }else {
           RPN calc = new RPN(line);
           System.out.printf("Answer is %f\n", calc.get( ));
}
}
}

Answer 1

CODE

import java.util.Scanner;

class StackNode {

public double data;

public StackNode next;

public StackNode(double data) {

this.data = data;

this.next = null;

}

}

public class RPN {

private String command;

private StackNode top;

public RPN(String command) {

top = null;

this.command = command;

}

public void push(double new_data) {

StackNode new_node = new StackNode(new_data);

if (top == null) {

top = new_node;

return;

}

new_node.next = top;

top = new_node;

}

public double pop() {

if (top == null) {

throw new IllegalArgumentException();

}

double top_data = top.data;

top = top.next;

return top_data;

}

public double get( ) {

double a, b;

int j;

for(int i = 0; i < command.length( ); i++) {

if(Character.isDigit(command.charAt(i))) {// if it's a digit

double number;

String temp = "";// get a string of the number

for(j = 0; (j < 100) && (Character.isDigit(command.charAt(i)) || (command.charAt(i) == '.')); j++, i++) {

temp = temp + String.valueOf(command.charAt(i));

}

// convert to double and add to the stack

number = Double.parseDouble(temp);

push(number);

}else if(command.charAt(i) == '+') {

b = pop( );

a = pop( );

push(a + b);

}else if(command.charAt(i) == '-') {

b = pop( );

a = pop( );

push(a - b);

}else if(command.charAt(i) == '*') {

b = pop( );

a = pop( );

push(a * b);

}else if(command.charAt(i) == '/') {

b = pop();

a = pop();

push(a / b);

}else if(command.charAt(i) == '^') {

b = pop( );

a = pop( );

push(Math.pow(a, b));

}else if(command.charAt(i) != ' ') {

throw new IllegalArgumentException( );

}

}

double val = pop( );

if(top != null) {

throw new IllegalArgumentException( );

}

return val;

}

public static void main(String args[]) {/* main method */

while(true) {

Scanner in = new Scanner(System.in);

System.out.println("Enter RPN expression or \"quit\".");

String line = in.nextLine( );

if(line.equals("quit")) {

break;

}else {

RPN calc = new RPN(line);

System.out.printf("Answer is %f\n", calc.get( ));

}

}

}

}