Generics inheritance is a teeny bit tricky because it's different from regular object inheritance, but we'll have all that cleared up in no time!
Take a look at this code.
Integer b = new Integer(); Number a = b;
It runs just fine since Integer is a subclass of Number.
Now let's try the same logic using generics.
ArrayList<Integer> intList = new ArrayList<>(); ArrayList<Object> objList = intList; // Compile time error
When we try to compile this, we get and error.
Test.java:9: error: incompatible types: ArrayList<Integer> cannot be converted to ArrayList<Object>
We would think that this would work, because
Integer is a subclass of
Object. However, it doesn't work because generics do not work like that.
ArrayList<Integer> is not subtype of
ArrayList<Object>, even though Integer is a subclass of Object. If we want to use generics on a more general level, we need to use wildcards, which are denoted by a
This a very important concept! Make sure you understand this before moving on.
Designed for serious programmers, this reliable, unbiased, no-nonsense tutorial illuminates key Java language and library features with thoroughly tested code examples. As in previous editions, all code is easy to understand, reflects modern best practices, and is specifically designed to help jumpstart your projects.$ Check price
Command Line Kung Fu is packed with dozens of tips and practical real-world examples. You won't find theoretical examples in this book. The examples demonstrate how to solve actual problems. The tactics are easy to find, too. Each chapter covers a specific topic and groups related tips and examples together.$ Check price