Compiler Design Experiment 8, evaluation of a post fix expression

PostFix.java

import java.util.*;

public class PostFix {



	public static void main(String[] args) {

	System.out.println("Input Postix Expression");

	String expression="";

	Scanner sc=new Scanner(System.in);

	expression=sc.nextLine();

	sc.close();

	System.out.println("Output= "+compute(expression));



	}

	public static double compute(String input)

	{

		

		Stack<Double> stack=new Stack<>();

		Scanner tokenizer=new Scanner(input);

	    while(tokenizer.hasNext()) 

	    {

	    	if(tokenizer.hasNextDouble()) 

	    	{

	    		Double s=tokenizer.nextDouble();

	    		stack.push(s);

	    	}

	    	else 

	    	{

	    		//code to compute addition subt, div, multi

	    		String op=tokenizer.next();

	    	    double num2=stack.pop();

	    		double num1=stack.pop();

	    		double result=perform(num1,num2,op);

	    		stack.push(result);

	    		

	    	}

	    	

	    }

	    return stack.pop();

	}

	public static double perform(double op1,double op2, String op) 

	{

		switch(op) 

		{

		case "+":

			return op1+op2;

		case "-":

			return op1-op2;

		case "*":

			return op1*op2;

		case "/":

			return op1/op2;

		default:

			return 0;

		}

	}



}