When to Import Interface, implement or do both?

When you see a statement like "import java.io.Serializable", it means that somewhere in your code file you intend to "use" this class in some manner. You can then refer to it in a shortened form as "Serializable". If you fail to have the import statement you can still use the class or interface in your code but must refer to it in its fully qualified form as "java.io.Serializable". When you "implement" an interface, you provide code that implements the "empty" member functions of the specified interface. An interface simply specifies what it does, not how it is accomplished. When you provide an implementation you determine how it is done. I suspect List was not followed by "implements List" because your code example has something like "List myList = new ArrayList();" If you look at ArrayList in the Java API documentation, you will see that it "implements the List interface". Comparable was not imported because it is part of the default java.lang package, which is imported by default.