javagenericsjava-5

ArrayList does not satisfy generic serializable list type


Given the following java code:

public static <I extends Serializable, L extends List<I> & Serializable> L getList() {
    return new ArrayList<I>(); // <-- Compile error
}

Given that ArrayList do extend both Serializable and List, why does it produce a compile error?

Incompatible types. Found: 'java.util.ArrayList<I>', required: 'L'


Solution

  • I came up with this solution:

    public interface SerializableList<T> extends List<T>, Serializable {
    }
    
    public class SerializableArrayList<T> extends ArrayList<T> implements SerializableList<T> {
        public SerializableArrayList(int initialCapacity) {
            super(initialCapacity);
        }
    
        public SerializableArrayList() {
        }
    
        public SerializableArrayList(Collection<? extends T> c) {
            super(c);
        }
    }
    

    Then whenever I need a Serializable List type, I can use the SerializableList interface and its implementation SerializableArrayList