InfixToPostfix.java

package com.sprint.datastructure;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
public class InfixToPostfix {
	
	public static List<Token> convert(String expr) {
		List<Token> inFixTokens = new TokenParser().parse(expr);
		List<Token> postFixTokens = new ArrayList<>();
		Stack<Token> opStack = new Stack<>();

		for (Token token : inFixTokens) {
			if (token.isOperator()) {
				while (!opStack.isEmpty()
						&& !token.hasHigherPriority(opStack.peek())) {
					postFixTokens.add(opStack.pop());
				}
				opStack.push(token);
			}

			if (token.isNumber()) {
				postFixTokens.add(token);
			}
		}

		while (!opStack.isEmpty()) {
			postFixTokens.add(opStack.pop());			
		}
		return postFixTokens;
	}
}