Java - Bounded Type Parameters
Table of Contents
1 - About
A generic method or class that operates on numbers will used bounded type parameters to restrict the type parameters accepted.
2 - Articles Related
3 - Syntax
The extends keyword, followed by one or several upper bounds.
If one of the bounds is a class, it must be specified first
<T (extends|super) B1 [& B2 & ... & Bn]>
where:
- B1 to Bn are class or interface that defined the bounds
- B2 to Bn are optional
- extends defined upper bounds
- super define lower bounds
In this context, extends is used in a general sense to mean either:
- extends (as in classes)
- implements (as in interfaces).
4 - Example
4.1 - Method
public <U extends Number> void inspect(U u)
4.2 - Class
public class NaturalNumber<T extends Integer> {
private T n;
public NaturalNumber(T n) { this.n = n; }
public boolean isEven() {
// intValue is methods defined in the bounds
return n.intValue() % 2 == 0;
}
// ...
}