9.2.1. Objectives¶

Upon completion of this module, students will be able to:

• Determine when a generic needs to be bounded

• Write and use methods and classes that use bounded generic parameters

• Write and use bounded generic methods

• Become familiar with syntax for wildcards

9.2.2. More on Generics¶

9.2.2.2. [10:53] Generics 2¶

Video Slides MoreOnGenerics.pdf

9.2.3. Sample Declarations of Generic Methods Explained¶

The format for declaring a Generic method is as follows:

methodModifiers <genericParameters> returnType methodName(methodParameters)

Note the use of the generic parameters placed inside the angle brackets.

Example 1

Below is one example of how you may declare a Generic method.

public static <T> void sort(T[] items, Comparator<? super T> comp)

The T following the static keyword and enclosed within the angle brackets represents the generic parameter for the sort method. The T should also appear in the method parameter list.

The second method parameter Comparator<? super T> comp is our way of specifying that comp must be an object that implements the Comparator interface for type T or for a superclass of type T

We use this approach to specify restrictions, for example, you can define a class that implements Comparator<Number> and use it to sort an array of Integer objects or an array of Double objects

Example 2

Below is another example Generic method declaration.

public static <T extends Comparable<T>> void sort(List<T> list)

The use of <T extends Comparable<T>> specifies that the generic parameter T must implement the interface Comparable<T>. The method parameter list (the object being sorted) is of type List<T>.

9.2.4. Checkpoint 1¶

9.2.5. Bounded Wildcard Examples¶

9.2.6. Programming Practice: Generics 1¶