Question

Description:
\\ implement in Java

Based on Chapter 6, programming project 1

Hewlett-Packard has a tradition of creating stack-based calculators. Rather than using standard algebraic notation ( 1 + 1 = ), the user would enter the values, then the operator. The calculator had an “enter” key to push each value onto a stack, then pop the stack when an operation key (e.g. “+” or “-”) was pressed.

Assignment:

Create a Calculator class that implements the provided StackCalculator interface

Requirement
Constructor:
+ Calculator()
   Precondition: none
   Postcondition: a new calculator with an empty number stack

Methods:
+ public void enter(String entry)
   Precondition: entry is either
   a double value (operand)
   a recognized operator [ +, -, *, /]
   Postcondition: if the entry is a double, the value is pushed onto the calculator’s number stack. If an operator, the top two values are popped from the stack, the operation performed, and the result pushed onto the stack. Note: the second operand is popped first.

+ double peek()
Precondition: number stack is not empty, otherwise throws EmptyStackException
Looks at the number at the top of this stack without removing it from the stack.

+ double pop()
Precondition: number stack is not empty, otherwise throws EmptyStackException
Removes the number at the top of this stack and returns that value.

+ void clear()
Removes all numbers from this stack. The stack will be empty after this call returns

+ boolean isEmpty
Tests If the number stack of this calculator is empty

+ int size()
Returns the number of values in this calculators number stack.

Answer 1

//StackCalculator.java

public interface StackCalculator {

       /*

       * Precondition: entry is either

             a double value (operand)

             a recognized operator [ +, -, *, /]

             Postcondition: if the entry is a double, the value is pushed onto the calculator’s number stack.

             If an operator, the top two values are popped from the stack, the operation performed, and the result pushed onto the stack.

             Note: the second operand is popped first.

       */

       public void enter(String entry);

       /*

       * Precondition: number stack is not empty, otherwise throws EmptyStackException

             Looks at the number at the top of this stack without removing it from the stack.

       */

       double peek();

       /*

       * Precondition: number stack is not empty, otherwise throws EmptyStackException

              Removes the number at the top of this stack and returns that value.

       */

       double pop();

       /*

       * Removes all numbers from this stack. The stack will be empty after this call returns

       */

       void clear();

       /*

       * Tests If the number stack of this calculator is empty

       */

       boolean isEmpty();

       /*

       * Returns the number of values in this calculators number stack.

       */

       int size();

}

//end of StackCalculator.java

//Calculator.java

import java.util.EmptyStackException;

import java.util.Stack;

public class Calculator implements StackCalculator{

      

       private Stack<Double> numberStack;

       /*

       * Precondition: none

             Postcondition: a new calculator with an empty number stack

       */

       public Calculator()

       {

             numberStack = new Stack<Double>();

       }

      

       @Override

       public void enter(String entry) {

            

             if(entry.equalsIgnoreCase("+") || entry.equalsIgnoreCase("-") || entry.equalsIgnoreCase("*") || entry.equalsIgnoreCase("/"))

             {

                    double op2 = pop();

                    double op1 = pop();

                    switch(entry)

                    {

                    case "+":

                           numberStack.push(op1 + op2);

                           break;

                    case "-":

                           numberStack.push(op1 - op2);

                           break;

                    case "*":

                           numberStack.push(op1*op2);

                           break;

                    case "/":

                           numberStack.push(op1/op2);

                           break;

                    }

             }else {

                    numberStack.push(Double.parseDouble(entry));

             }

       }

       @Override

       public double peek() {

             if(isEmpty())

                    throw new EmptyStackException();

             else

                    return numberStack.peek();

       }

      

       @Override

       public double pop() {

             if(isEmpty())

                    throw new EmptyStackException();

             else

                    return numberStack.pop();

       }

       @Override

       public void clear() {

             while(!isEmpty())

             {

                    numberStack.pop();

             }

       }

       @Override

       public boolean isEmpty() {

             return(numberStack.isEmpty());

       }

       @Override

       public int size() {

             return numberStack.size();

       }

}

//end of Calculator.java