Can someone please explain me this class definition statement
public class BinarTree<Type extends Comparable<Type>> {...
I completely understand the purpose of it but not the syntax. According to me it should be just
public class BinarTree<Type extends Comparable> {...
What's the meaning of
<Type extends Comparable<Type>> ?
^^^^
Comparable is a generic interface. The reason behind that is to avoid casting to a specific type in the Comparable#compareTo(...) method.
So if a Type extends Comparable<Type> this would mean that the Type will derive a method with signature
public int compareTo(Type t1)
instead of
public int compareTo(Object o1)
The interface Comparable is itself a template.
So what you have there is a template with a parameter that must extend a template.
And specifically it must extend a template that received the extending class as a parameter.
Comparable is a template for interfaces that implement an order relationship and implement the method int compareTo(TYPE o).
So it's normal to define a class:
class FooBar implements Comparable<FooBar> {...
A binary tree wouldn't work for a class that was declared:
class FooBar implements Comparable<Snafu> {...
That's because you would be able to compare FooBars to Snafus but not each other.
In
public class BinarTree<Type extends Comparable>{...
Type can be any Comparable, also Comparable<Integer> or Comparable<OtherType>. If this is what you want, it is fine. Most times, I think you know what you want to compare exactly, so specialize the Comparable to Comparable<Type>
Comparable<?> and not the raw type Comparable if that is what I wanted. Avoid using raw types - they only exist for backward compatibility with old Java versions.