Question

The objectives of this assignment are to:

1. Further enhance your knowledge and skill in Java.
2. Gain an understanding and experience with stacks.
3. Gain further experience using generics.
4. Continue to practice good programming techniques.

Create a stack class named MyStack that stores generics with the methods shown below. Write a test program that thoroughly tests your stack implementation.

void push(E item)	push item onto top of stack
E peek()	return item on top of stack
E pop()	return item on top of stack and remove it from the stack
boolean isEmpty()	returns whether or not stack is empty

Once the stack is working, create a class EvalPostfix that receives a postfix expression in String format, uses the MyStack class to evaluate the expression, and returns the resulting value. You may assume that all operands and operators (+ - * /) will be separated by a single space. Operands will be integers and may contain several digits. The class will require the following functions to be implemented:

EvalPostfix(String post)	constructor that sets the attribute containing the postfix string to be evaluated
int eval()	returns the result of the postfix expression

Write a test program named Prog5 that gets a postfix expression from the keyboard, uses EvalPostfix to evaluate the expression, and displays the result.

Requirements

• Your source code should abide by the Java programming standards for the course.
• Your source code should be documented using Javadoc style according to the course standards.
• Use the default package in your project; do not specify a package in your code.
• Use any file and class names specified in the assignment.
• Your test program must be named Prog5.

Preparation for submission:

After you have completed the program, put all of the .java files (Prog5.java, MyStack.java, and EvalPostfix.java) into a zip file named YourLastName5.zip with no subdirectory structure.

Answer 1

Done. Please have a look and incase of any doubt leave a comment.

//////////////////////////////////////MyStack.java/////////////////////////////////

public class MyStack<T> {
   private T t[];

   private final static int DEFAULT_SIZE = 10;
   private int top;

   // default constructor sets the array to default capacity
   public MyStack() {
       this(DEFAULT_SIZE);
   }

   // constructor with specified size sets the size of the array to the given size
   public MyStack(int size) {
       t = (T[]) new Object[size];
       top = -1;
   }

   /**
   *
   * @return true if stack is empty otherwise false
   *
   */
   public boolean isEmpty() {
       return (top == -1);
   }

   /**
   * The method checks if the stack is not empty and then gets the value.
   *
   * @return return the top item and removes it from stack (if not empty)
   */
   public T pop() {
       if (top == -1)
           return null;
       return t[top--];
   }

   /**
   * Adds the item to the top of the stack
   *
   * @param elem
   */
   public void push(T elem) {
       t[++top] = elem;
   }

   /**
   *
   *
   * @return returns the total number of elements in the stack
   */
   public int size() {
       return (top + 1);
   }
}

/////////////////////////////////////ENd MyStack.java////////////////////////////////////////////

/////////////////////////////////////EvalPostfix.java///////////////////////////////////////////////

import java.util.Scanner;

//Class which is responsible for evaluating postFIx expression by putting elements on stack one by one
public class EvalPostfix {
   // string to evaluate
   private String str;

   // Constructor that intialise the string
   public EvalPostfix(String s) {
       this.str = s;
       int ans = evalPf();
       System.out.println("The result after evaluatins: " + s + " is = " + ans);
   }

   /**
   *
   * @return
   */
   public int evalPf() {
       // create new stack
       MyStack<Integer> myStack = new MyStack<Integer>();

       Scanner scanner = new Scanner(this.str);
       // scanner reads number by number seperated by white space to put the numbers in
       // to the stack
       while (scanner.hasNext()) {
           if (scanner.hasNextInt()) {
               myStack.push(scanner.nextInt());
               continue;
           }
           // take out first two values from the stack
           int operand1 = myStack.pop();
           int operand2 = myStack.pop();

           char op = scanner.next().charAt(0);
           // push the result it into the stack
           if (op == '+')
               myStack.push(operand2 + operand1);
           else if (op == '-')
               myStack.push(operand2 - operand1);
           else if (op == '*')
               myStack.push(operand2 * operand1);
           else if (op == '/')
               myStack.push(operand2 / operand1);
           else if (op == '%')
               myStack.push(operand2 % operand1);
       }

       scanner.close();
       return myStack.pop();
   }
}

/////////////////////////////////////End EvalPostfix.java///////////////////////////////////////////////

//////////////////////////////////////////Prog5.java///////////////////////////////////////////////////////

import java.util.Scanner;

//This is the program to test stacks and EvalPostfix program
public class Prog5 {
   public static void main(String args[]) {
       char c = 'y';
       Scanner sc = new Scanner(System.in);
       do {
           System.out.println("Please enter a experssion to Evaulate");
           // get user input
           String str = sc.nextLine();
           //call construtor
           EvalPostfix eval = new EvalPostfix(str);
           System.out.println("Do you want to evaluate more expressions");
           c = sc.nextLine().charAt(0);
       } while (c == 'y' || c == 'Y');
       sc.close();
   }
}

//////////////////////////////////////////End Prog5.java///////////////////////////////////////////////////////

Output Screenshot