implement a simple class that represent a mathematical set with only one meaningful operation add

package lab1;

public class Set {

private String items;

private int size;

private int capacity;

public Set (int capacity){

}

public int size(){

this.size=size;

return size;

}

public int capacity(){

this.capacity = capacity;

return capacity;

}

public String toString(){

return null;

}

public boolean add(String thing){

if(thing == itmes){

return true;

}

else

{

return false;

}

}

}