Scenario

We are used to writing mathematical expressions in the form of 1 + 2 * 3. This type of notation is called an infix. Using infix notation, an operator is always in between two operands. There is a different notation called postfix, where the operator is after the operands. Examples of such expressions are shown in the following table:

Infix expression	Postfix expression
1 + 2	1 2 +
1 + 2 * 3	1 2 3 * +
(1 + 2) * 3	1 2 + 3 *
5 + 4 / 2 * 3	5 4 2 / 3 * +

Aim

Implement an algorithm that accepts a postfix string, evaluates it, and returns the result.

Prerequisites

• Implement the following method:

  public double evaluate(String postfix) { //... }

• Assume the operator and operands are always separated by a space, such as "5 2 +". The input string will look like the examples shown in the preceding table

Steps for Completion

1. Use the stack data structure to solve this problem.
2. Start processing the expression from left to right.
3. If you encounter a numeric operand, push it on the stack.
4. If you encounter an operator, pop two items from the stack and perform the operation accordingly (addition, subtraction, and so on) and push the result back on the stack.
5. Once you have processed the entire expression, the result should be the on the top of the stack.

Task

1.Implement the evaluate() method.

2.Use the stack data structure to solve this problem.

3.Program properly evaluates operators.

public class EvalPostfix { // Write your code here public static void main(String[] args) { /* * This main method is a stub. * It does nothing. * Feel free to write your own code to test your implementation. * In this case, we have nothing actionable in here, just this comment block, so the JVM should rapidly lose interest and move on to the rest of your code. */ } }