You cannot add non-related class to generic collection instance : generics « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. generics

import java.util.Vector;

public class MainClass {
  public static void main(String[] argv) {
    Vector<MyClass> myVec;
    myVec = new Vector<MyClass>();
    MyClass myClass = new MyClass();
    myVec.add(myClass);

    myVec.add("");

  }
}

class MyClass {
}

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	The method add(MyClass) in the type Vector is not applicable for the arguments (String)

	at MainClass.main(MainClass.java:10)