Thread: Convert Expressions to RPN format using tree

I am trying to fix my code it is duplicating the last output twice
For inputs you must have spaces. I have attached an snippet of the output.
My code is converting 1 + 1 into an RPN format 1 1 +
I am grateful for any help provided

import java.util.ArrayList;
import java.util.Scanner;
import java.util.regex.Pattern;
 
public class ToPostFix {
 
static 	ArrayList<String> al= new ArrayList<String>();
static  ArrayList<String> alex= new ArrayList<String>();
static String value;
static String exp;
	public static void main(String[] args) {
		System.out.println("Enter your inputs");
		 Scanner in = new Scanner (System.in);
		String input = in.nextLine();
		String[] tokens = input.split("\\s");
		in.close();
	for (int i=0; i<tokens.length; i++) {
		validate(tokens[i]);
	}
	   for (String x : tokens) {
 
			al.add(x);
			}
 
	    firstcheck();
	    secondcheck();
	    thirdcheck();
 
	   String[] tokens2= alex.get(alex.size()-1).split("\\s");
 
 
	    TreeNode myTreeNode = new TreeNode(value, null);
	    myTreeNode.setValue((tokens2[1]));
		myTreeNode.setLeft(new TreeNode(tokens2[0], myTreeNode));
		myTreeNode.setRight(new TreeNode(tokens2[2], myTreeNode));
	    tree(alex,myTreeNode);
	    ToPostFix.postOrder(myTreeNode);
	}
 
	static void firstcheck() {	   
	   for(int i = 0; i < al.size() - 1; i++) {
		   if(al.get(i).equals("(")) {
 
			   String exp;
			   exp = al.get(i+1) +" "+ al.get(i+2)+" " + al.get(i+3);
			   alex.add(exp);
			   al.remove(i);
			   al.remove(i);
			   al.remove(i);
			   al.remove(i);
			   al.remove(i);
			   al.add(1,  "exp" + (alex.size()-1));
		   }
 
	   }
		}
		static void secondcheck() {
		   //user regex for that
		   for(int j = 0; j < al.size() - 1; j++) {
			   if(al.get(j).equals("*") || al.get(j).equals("/") || al.get(j).equals("%")) {
 
				   String exp;
				   exp = al.get(j-1) +" "+ al.get(j)+" " + al.get(j+1);
				   alex.add(exp);
				   al.remove(j - 1); 
				   al.remove(j - 1); 
				   al.remove(j - 1);
				   al.add(j - 1,  "exp" + (alex.size()-1));
			   }  
		   }
		}
		static void thirdcheck()
		{  
 
			   for(int k = 0; k <= al.size() - 1; k++) {
				   if(al.get(k).equals("+") || al.get(k).equals("-")) {
 
					   String exp;
					   exp = al.get(k-1) +" "+ al.get(k)+" " + al.get(k+1);
					   alex.add(exp);
					   al.remove(k - 1); 
					   al.remove(k - 1);
					   al.remove(k - 1);
					   al.add(k-1,  "exp" + (alex.size()-1));
					   k -= 1;
 
				   }   
				   System.out.println(al.size());
			   }
		}
 
		static void tree(ArrayList<String>alex, TreeNode myTreeNode)	{
 
			if(myTreeNode.getLeft().getValue().substring(0,1).equals("e")) {
 
			String[] tokens2= alex.get(alex.size()-1).split("\\s");
			TreeNode newNode = new TreeNode(tokens2[1], myTreeNode);
			newNode.setLeft(new TreeNode(tokens2[0], newNode));
			alex.remove(alex.size()-1);
			newNode.setRight(new TreeNode(tokens2[2],newNode));
			myTreeNode.setLeft(newNode);
 
			tree(alex,newNode);
		}
 
		if(myTreeNode.getRight().getValue().substring(0,1).equals("e")) {
 
			String[] tokens2= alex.get(alex.size()-1).split("\\s");
			TreeNode newNode = new TreeNode(tokens2[1], myTreeNode);
			newNode.setLeft(new TreeNode(tokens2[0], newNode));
			alex.remove(alex.size()-1);
			newNode.setRight(new TreeNode(tokens2[2],newNode));
			myTreeNode.setRight(newNode);
			tree(alex,newNode);
		}
 
 
		}
		static void postOrder(TreeNode myTreeNode) {
		if(myTreeNode != null) {
			postOrder(myTreeNode.left);
			postOrder(myTreeNode.right);
 
			System.out.printf( myTreeNode.value);
			}
		}
 
 
	static boolean validate (String s) {
		String regex = "[*/+\\-%]|[()]|\\-?[0-9][\\.0-9]*"; // double forward slash is used to escape, example it would think it was going from 0-9
												//* means 0 or more
												//. means floating point
												//-? allows negative numbers 
												// ? is used as optional
		//if (false)
			//return System.out.println("The input is wrong");
 
 
		return (Pattern.matches(regex, s));
 
	}
 
}

code RPN converter.jpgError RPN Converter.jpg

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