Question

I have a generic class which extends another generic class.

The abstract class has 2 type parameters, but I need only one in my functions.

Is it save to just assign it a random like String type, or are there any drawbacks to this?

public abstract class AbstractFoo<T, B>
{
   public abstract void read(T item);
}

public class LittleFoo extends AbstractFoo<byte[], String>
{
   @Override
   public void read(byte[] item)
   {
      // work here
   }
}

Answer 1

No there really isn’t any drawback to this, and it seems like a simple way to do it in my opinion.

Also, you might want to consider using composition instead of extension. For example, take a look at the HashSet implementation from java.util:

87   public class HashSet<E>
88       extends AbstractSet<E>
89       implements Set<E>, Cloneable, java.io.Serializable
90   {
91       static final long serialVersionUID = -5024744406713321676L;
92   
93       private transient HashMap<E,Object> map;
94   
95       // Dummy value to associate with an Object in the backing Map
96       private static final Object PRESENT = new Object();

A HashSet is basically a HashMap, but only considers the set of keys (hence the dummy variable PRESENT, which is just a placeholder). You could perhaps do something similar.