Applying Common Patterns with Generics

Generics in Java provide a powerful way to create reusable code by enabling the definition of classes, methods, and interfaces that can work with different types of data. In this article, we'll explore some common patterns that can be applied when using generics, allowing for even more flexibility and robustness in our code.

1. Generic Classes

One of the most straightforward ways to use generics is by creating generic classes. These classes can work with any type specified when instantiated. For example, let's say we want to create a Box class that can hold any kind of object. We can define it as follows:

public class Box<T> {
    private T contents;
    public void setContents(T contents) {
        this.contents = contents;
    public T getContents() {
        return contents;

Here, the T is a type parameter that can be replaced by any type when creating an instance of Box. This allows us to create boxes that can contain integers, strings, or any other object type.

2. Generic Interfaces

Generics can also be used in interfaces. This pattern is particularly useful when defining interfaces for collections or data structures. For instance, let's say we want to create an interface for a List implementation that can be used with any type:

public interface List<T> {
    void add(T element);
    void remove(T element);
    T get(int index);
    // Other methods...

By using generics in the interface, we can define methods that work with any type of data, making it more flexible and reusable.

3. Wildcards

Wildcards in generics allow us to work with unknown types. There are two types of wildcards: ? (unbounded wildcard) and ? extends Type (bounded wildcard). The unbounded wildcard can be used when we don't care about the specific type, while the bounded wildcard restricts the possible types to subclasses of a particular class (including the class itself) or interfaces that the type implements.

For example, suppose we have a method that accepts a list of any type and prints its elements:

public static void printList(List<?> list) {
    for (Object element : list) {

Here, the unbounded wildcard ? allows us to accept lists of any type. This method can be called with a List<Integer>, List<String>, or any other List.

4. Generic Methods

Generics can also be applied at the method level. This pattern allows us to create methods that can work with different types independently of the class they belong to. For example:

public class Utils {
    public static <T> T getLastElement(List<T> list) {
        if (list.isEmpty()) {
            throw new IllegalArgumentException("The list is empty");
        return list.get(list.size() - 1);

In this case, the method getLastElement is declared with a type parameter T. This method can be used with any type of List, and it will return the last element.


Generics in Java provide a powerful way to write reusable and type-safe code. By applying common patterns such as generic classes, interfaces, wildcards, and methods, we can create more flexible and robust programs. Understanding and mastering generics is essential for any Java developer striving to write efficient and adaptable code.

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