Question

Write a Java program that will implement a stack object to convert from either infix notation to postfix notation or postfix notation to infix notation.  The program will also implement a link list data structure to track all the conversions done. The Program should have a menu like the following as its output:

"Please select what type of conversion you would like to do:

1. Infix to postfix
2. Postfix to infix
3. Print Equations
4. Exit"

Answer 1

Screenshot

import java.util.Scanner; import java.util.Stack; /** * Program to convert inf to post and post to inf * Get user has choice for convertion type * Prompt for expression * store each conversion in linkedlist * Display all evaluated expressions * @author deept <terminated> Convertor (Java Application] C:\Program FilesVava jre1.8.0_161 Please select what type of conversion you would like to do 1. Infix to postfix 2. Postfix to infix 3. Print Equations 4. Exit Enter an infix expression: 2+5 ** 2+5 = 25+ Please select what type of conversion you would like to do 1. Infix to postfix 2. Postfix to infix 3. Print Equations 4. Exit public class Convertor { //Scanner object for read public static Scanner sc=new Scanner(System.in); public static void main(String[] args) { //Call menu int op=menu(); //Create a linkeslist object MyLinkedList list=new MyLinkedList(); // Loop until exit while(op!=4){ if(op==1) { System.out.println("\nEnter an infix exp String inf=sc.nextLine(); String postfix=infixToPostfix(inf); list.insertItem(inf, postfix); System.out.println(inf+" = "+postfix); Enter an postfix expression: 25+ 25+ = (2+5) else if (op==2) { System.out.println("\nEnter an postfix expression: "); String postfix=sc.nextLine(); String inf=postfixToInfix(postfix); list.insertItem(postfix,inf); System.out.println(postfix+" = "+inf); else {
Program

MyLinkedlist.java

//Create a class node
class MyNode{
   String exp1,exp2;
   char op;
   MyNode next;
   public MyNode(String exp1,String exp2) {
       this.exp1=exp1;
       this.exp2=exp2;
       op='=';
       next=null;
   }
}
//Create orderedr list class
public class MyLinkedList {
   //Instance variable
   MyNode head;
   //Constructor
   public MyLinkedList() { // constructors always have the same name as the class
       head=null;
     }
   //Insert an element last into list
   public void insertItem(String exp1,String exp2) {
       MyNode newNode=new MyNode(exp1,exp2);
       if(head==null) {
           head=newNode;
       }
       else {
           MyNode temp=head;
           while (temp.next != null) {
               temp = temp.next;
       }
       // Insert the new_node at last node
       if(temp.next==null) {
           temp.next = newNode;
        }
    }
}
@Override
public String toString() {
String tempStr = "";
MyNode temp=head;
while(temp.next!=null) {
   tempStr = tempStr+temp.exp1+" "+temp.op+" "+temp.exp2+"\n";
    temp = temp.next;
}
tempStr = tempStr+temp.exp1+" "+temp.op+" "+temp.exp2;
return tempStr;
}

}

Convertor.java

import java.util.Scanner;
import java.util.Stack;
/**
* Program to convert inf to post and post to inf
* Get user has choice for convertion type
* Prompt for expression
* store each conversion in linkedlist
* Display all evaluated expressions
* @author deept
*
*/
public class Convertor {
   //Scanner object for read
   public static Scanner sc=new Scanner(System.in);
   public static void main(String[] args) {
       //Call menu
       int op=menu();
       //Create a linkeslist object
       MyLinkedList list=new MyLinkedList();
       //Loop until exit
       while(op!=4) {
           if(op==1) {
               System.out.println("\nEnter an infix expression: ");
               String inf=sc.nextLine();
               String postfix=infixToPostfix(inf);
               list.insertItem(inf,postfix);
               System.out.println(inf+" = "+postfix);
           }
           else if(op==2) {
               System.out.println("\nEnter an postfix expression: ");
               String postfix=sc.nextLine();
               String inf=postfixToInfix(postfix);
               list.insertItem(postfix,inf);
               System.out.println(postfix+" = "+inf);
           }
           else {
               System.out.println("\nExpressions evaluated:-\n"+list);
           }
           System.out.println();
           op=menu();
       }
       System.out.println("\nGoodbye!!!");
   }
  
   /*
   * Method to get user options
   * Display options
   * Return option
   */
   public static int menu() {
       System.out.println("Please select what type of conversion you would like to do:\n"+
                           "1. Infix to postfix\n2. Postfix to infix\n3. Print Equations\n"+
                           "4. Exit");
       int opt=sc.nextInt();
       //Error check
       while(opt<1 || opt>4) {
           System.out.println("\nERRROR!!!Option should be 1-4.Please Re-enter....\n");
           System.out.println("Please select what type of conversion you would like to do:"+
                    "1. Infix to postfix\n2. Postfix to infix\n3. Print Equations\n"+
                    "4. Exit");
            opt=sc.nextInt();
       }
       sc.nextLine();
       return opt;
   }
   /*
   *Method to get precedence of operator here
   * multiplication division has higher precedence than
   * Addition and subtraction
   */
   public static int precedenceFinder(char op) {
       if(op=='+' || op=='-') {
           return 1;
       }
       else if(op=='*' || op=='/') {
           return 2;
       }
       else {
           return -1;
       }
   }
   /*
   * Method to convert infix to postfix
   * Take an infix expression as input
   * Convert into postfix and return
   */
   public static String infixToPostfix(String infix) {
            String postfix ="";
            //Stack for temporary save
            Stack<Character> stack = new Stack<>();
             //Loop through characters of infix expression
            for (int i = 0; i<infix.length(); ++i)
            {
                char c = infix.charAt(i);
                //Is it digit add into postfix
                if (Character.isLetterOrDigit(c)) {
                   postfix+=c;
                }
                //Check for opening brace
                else if (c == '(') {
                   stack.push(c);
                }
                //Check for closing brace
                else if (c == ')')
                {
                   //The take elements from stack to add into postfix
                    while (!stack.isEmpty() && stack.peek() != '(') {
                       postfix+=stack.pop();
                    }
                    //If nothing inside stack means invalid expression
                    if (!stack.isEmpty() && stack.peek() != '(')
                        return "Invalid Expression";             
                    else
                        stack.pop();
                }
                //If operator get then find out precedence
                else
                {
                    while (!stack.isEmpty() && precedenceFinder(c) <= precedenceFinder(stack.peek())){
                        if(stack.peek() == '(') {
                           return "Invalid Expression";
                        }
                        postfix += stack.pop();
                    }
                    stack.push(c);
                }
         
            }
           //Pop until end of stack
            while (!stack.isEmpty()){
                if(stack.peek() == '(') {
                   return "Invalid Expression";
                }
                postfix += stack.pop();
             }
            return postfix;
        }
     
   /**
   * Method to generate infix from given postfix expression
   * Loop through each character to seperate operator and operand
   * Use stack for temporary storage and evaluate infix and return
   * @param exp
   * @return
   */
   public static String postfixToInfix(String post)
   {
       //Temporary storage
         Stack<String> stack = new Stack<String>();
         //Loop until end of th estring
         for (int i = 0; i < post.length(); i++)
         {
             //Check fo roperand
             if (Character.isLetterOrDigit(post.charAt(i))) {
               stack.push(post.charAt(i) + "");
             }
             //Check for operator
             else
             {
                 String op1 = stack.peek();
                 stack.pop();
                 String op2 = stack.peek();
                 stack.pop();
                 stack.push("(" + op2 + post.charAt(i) + op1 + ")");
             }
         }
     
        //last element from stack
         return stack.peek();
   }
}

--------------------------------------------------------------

Output

Please select what type of conversion you would like to do:
1. Infix to postfix
2. Postfix to infix
3. Print Equations
4. Exit
1

Enter an infix expression:
2+5
2+5 = 25+

Please select what type of conversion you would like to do:
1. Infix to postfix
2. Postfix to infix
3. Print Equations
4. Exit
2

Enter an postfix expression:
25+
25+ = (2+5)

Please select what type of conversion you would like to do:
1. Infix to postfix
2. Postfix to infix
3. Print Equations
4. Exit
3

Expressions evaluated:-
2+5 = 25+
25+ = (2+5)

Please select what type of conversion you would like to do:
1. Infix to postfix
2. Postfix to infix
3. Print Equations
4. Exit
4

Goodbye!!!