Question: How do i output the sum after each postfix notation? Every time i run the program i get Stack Exception error. Here is my code
How do i output the sum after each postfix notation? Every time i run the program i get Stack Exception error.
Here is my code below:
----------------------------------------------------
--test class-
import java.util.*;
import java.io.*;
public class Main {
public static void main(String args[]) throws IOException //driver program
{
FileOutputStream toFile=null;
Scanner fromFile=null;
PrintStream ps=null;
fromFile = new Scanner(new File("lab.txt")); //Reads from lab.txt file
toFile= new FileOutputStream("output.txt"); //outputs to the output.txt file
ps=new PrintStream(toFile); //prints output from lab.txt to output.txt
Stacks stack = new Stacks(); //Instantiate stack object from stack class
String token=" "; //string token to hold input from lab.txt
while(fromFile.hasNext()) //keep reading until end of file
{
token=fromFile.nextLine(); //stores string into token variable
System.out.println(stack.infixToPostfix(token)+" = "+ stack.sumPostfix(token));
//ps.println(stack.infixToPostfix(token));
}//end of loop
fromFile.close(); //close files
toFile.close();
}
}//end of program
------------------------------------------------
-stack class--
import java.util.Stack;
//Stack class that utilizes all methods to properly run a stack object
public class Stacks implements StackInterface{
private Node top; //head node
class Node{ //Node class
private char item; //item variable of type character to store input from lab.txt
private Node next; //moves to next node in stack
Node(char newItem) //constructor that takes one parameter of type char
{
item=newItem; //assigns value of incoming parameter to item
next=null;
}
Node(char newItem, Node nextNode) //constructor takes two parameters a char and a node
{
item=newItem; //assigns value of incoming parameter to item
next=nextNode;
}
}//end node class
Stacks(){ //Stacks class Constructor
top=null; //Assigns the Node variable top to null
}
@Override
public boolean isEmpty() { //override method that checks to see if the stack is empty
// TODO Auto-generated method stub
return top==null; //returns true if it is empty otherwise returns false
}
@Override
public void popAll() { //removes all items from the stack
// TODO Auto-generated method stub
top=null;
}
@Override
public void push(char newItem) { //push inserts a new item to the top of the stack and takes the parameter of type char
// TODO Auto-generated method stub
top= new Node(newItem, top); //assigns new item to top node
}
@Override
public char pop() throws StackException{ //removes one element from the top of the stack
if(!isEmpty()) { //if stack is not empty
//the node added most recently is popped or removed from the stack
Node temp=top;
top=top.next;
return (char) temp.item; //return the temp node value
}
else //if stack is empty return exception
{
throw new StackException("StackException on"
+ "pop: Stack empty");
}
}
@Override
public char peek() throws StackException { //retrieves top of the stack
if(!isEmpty()) //if the stack is not empty
{
return (char) top.item; //the item that was received most recently is returned however,
//the stack remains unchanged
}
else
{
throw new StackException("StackException on" //if the stack is empty then an empty stack exception is thrown
+"peek:stack empty");
}
}
public int precedence(char token) //function that will return the precedence of a given operator
//within the lab.txt expression
{ //the higher the return value the higher the precedence of the operator
switch(token) //switch statement that takes char token : PEMDAS to decide precedence
{
case '+':
case '-':
return 1; //low precedence
case'*':
case '/':
return 2;
case'^':
return 3; //highest precedence
}
return -1;
}//end
public String infixToPostfix(String expression) //converts infix expressions to postfix and takes a parameter of type String
{
String result= new String(""); //String result to hold incoming data from lab.txt
Stacks stack = new Stacks(); //create stack object from stacks class
for(int x=0;x { char c=expression.charAt(x); if(Character.isLetterOrDigit(c)) //if the scanned char is an operand add it to result { result+=c+" "; } else if(c=='(') //if scanned char is a '(' push it to the stack { stack.push(c); } else if (c==')') // If the scanned character is an ')', pop and output from the stack { while(!stack.isEmpty() && stack.peek() != '(') { //if stack is not empty and '(' in the stack //add expression to result result+=stack.pop(); } if(!stack.isEmpty() && stack.peek()!='(') { return "Invalid Expression"; //invalid expression in the string } else { stack.pop(); } } else //an operator is encountered { while( !stack.isEmpty() && precedence(c)<=precedence(stack.peek())) //while stack is not empty and the string in precedence is less than //or equal to the value of thats at the top of the stack { result+=stack.pop(); //then add operator to result } stack.push(c); //add Element to the stack } } while(!stack.isEmpty()) { result+=" "+stack.pop(); //pop all the operators from the stack } return result; //return the String result } public int sumPostfix(String expression) { Stack for(int i=0; i { char c= expression.charAt(i); if(Character.isDigit(c)) { stacks.push(c - '0'); } else { int val1 = stacks.pop(); int val2=stacks.pop(); switch(c) { case '+': stacks.push(val2+val1); break; case '-': stacks.push(val2- val1); break; case '/': stacks.push(val2/val1); break; case '*': stacks.push(val2*val1); break; } } } return stacks.pop(); } } ---------------------------------------------------------------------------- --input file: lab.txt--- 5 5-3 5*(3+4) 7*3+5*6 2+5*(7+8)/3 (5) 3+4*5+6 9-4*(5-3) 1*2*3*4*5*6*7 (2+4)*(8-6) 3+4 9-1-2-3 2*(((4+2))) (((((5))))) 3*7-4*2+5*6 3*5 (3*(9-7*1))/2+5 6+9*(5*(3+4)) 1+2+3+4+5 9/3+8/2
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