Java Language
- Getting started with Java Language
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- Creating a Generic Class
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- Different ways for implementing a Generic Interface (or extending a Generic Class)
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- Referring to the declared generic type within its own declaration
- Requiring multiple upper bounds ("extends A & B")
- The Diamond
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Java Language Generics Requiring multiple upper bounds ("extends A & B")
Example
You can require a generic type to extend multiple upper bounds.
Example: we want to sort a list of numbers but Number doesn't implement Comparable.
public <T extends Number & Comparable<T>> void sortNumbers( List<T> n ) {
Collections.sort( n );
}
In this example T must extend Number and implement Comparable<T> which should fit all "normal" built-in number implementations like Integer or BigDecimal but doesn't fit the more exotic ones like Striped64.
Since multiple inheritance is not allowed, you can use at most one class as a bound and it must be the first listed. For example, <T extends Comparable<T> & Number> is not allowed because Comparable is an interface, and not a class.
