ArrayList class .add error

Question

I am currently learning about arrays and the weblesson from my class is teaching me about the ArrayList class. I tried to make my own array to try it out, but when I followed the format the weblesson showed me, I get a compiler error that reads: "no suitable method found for add(java.lang.String)". While highlighting the ".add".

import java.util.ArrayList;
public class String
{
 ArrayList <String> myArrayList;
 public void arrayTest()
 {
 ArrayList <String> names = new ArrayList <String> ();
 names.add("John");
 names.add("Smith");
 names.add("Matt");
 System.out.println(myArrayList.get(1));
 }
}

• Pshemo: To answer your next question about NullPointerException: you created one ArrayList and stored it in names reference, then you filled it with data, but in next step you are trying to read data from uninitialized myArrayList reference.

Answer 1

Your class is hiding java.lang.String so there is a type mismatch between the argument used for the add method and your custom String class. Rename it to something else other than String

Answer 2

The problem might be that your class is also called String. I'm guessing the generic type of your ArrayList is that and not the Java String.

Answer 3

What happens is that you are naming your class as String, which will make the compiler get confused because there already exist a built-in String.

What can you do?

• Rename your class, to something different:

  public class StringTest
  

• Or use the fully qualified class name (which I wouldn't recommend):

  ArrayList <java.lang.String> names = new ArrayList <java.lang.String> ();
  

Answer 4

Because you are naming your class String, the String in

ArrayList < String > names 

is referring to your self-defined class type. Therefore, only the 'String' objects that you defined can be added to the ArrayList, not the actual Java Strings. To correct this, name your class something else.