added comments on the methods & classes

src/Application.java

@@ -3,9 +3,13 @@ import java.util.List;
 
 public class Application {
     public static void main(String[] args) {
+        //List with a fitting String to be parsed into multiple tokens
         List<String> test = Arrays.asList("1 + xy^2 - (31 * x)y");
+        //Iterates through every String
         for (String value: test) {
+            //creates a list of tokens out of the String
             List<Lexer.Token> tokens = Lexer.lex(value);
+            //prints each token out (with .toString())
             for(Lexer.Token singleToken: tokens) {
                 System.out.println(singleToken.toString());
             }