Does Java 8 have generics?

Does Java 8 have generics?

I'd be happy to help!

Java 8 is a major release of the Java programming language, and it does introduce some significant features and improvements. One feature that's often misunderstood is its approach to generics.

Generics were first introduced in Java 5 (also known as J2SE 5.0). They allow you to specify the type(s) of objects that a class or method can work with. This helps prevent runtime errors by ensuring that, at compile-time, the types are compatible and safe.

In Java 8, generics haven't changed significantly. You can still use them to define classes, interfaces, methods, and constructors that operate on specific types. The main difference is that Java 8 adds some additional features and improvements related to type inference and lambda expressions.

Here's what you need to know:

List list = List.of("Hello", "World");

Instead of writing List<String> list = new ArrayList<String>(new String[] {"Hello", "World"});

List list = new ArrayList<>();
list.add(() -> "Hello");

This code creates an ArrayList and adds a lambda expression that returns the string "Hello". The type argument is inferred by the compiler, so you don't need to specify it explicitly.

public static  T getNumber(T number) {
return number;
}
List<? super Integer> list = List.of(1, 2, 3);

The getNumber method can work with any subtype of Number, such as Integer. The list variable is a List that can hold integers or other types (like Double). The ? super syntax allows you to specify that the list can contain elements of type Integer or its supertypes.

In summary, Java 8 does have generics, and they work similarly to how they did in previous versions. However, there are some new features and improvements related to type inference, lambda expressions, and wildcard types that can make your code more concise and flexible.

java generics wildcard

Java's Generics Wildcard!

In Java, Generics provide a way to parameterize types when working with collections and generic classes. This is useful for several reasons:

However, there are situations where you might need to create instances of classes using unknown types. This is where Java's Wildcard comes in handy!

What are Java's Wildcards?

Wildcard types, denoted by ?, represent unknown types. They can be used in place of type parameters or as upper bounds for generic methods.

Here's an example:

List numbers;

In this example, ? is a wildcard that represents some unknown type that extends the Number class (e.g., Integer, Double, etc.). The numbers list can store instances of any number subclass.

Upper and Lower Bounds

You can specify upper and lower bounds for wildcards using the extends and super keywords, respectively. For example:

Here's another example:

List integers;

In this case, the wildcard represents some unknown type that's an upper bound for Integer, meaning it can be either Integer itself or any of its subclasses.

Bounded Wildcards

Sometimes, you might want to restrict the types that a wildcard can represent. This is where bounded wildcards come in handy!

For example:

List serializableNumbers;

In this case, the wildcard represents some unknown type that's an upper bound for both Number and Serializable. This means you can only store instances of types that implement both Number and Serializable, such as Integer.

Tightening Bounds

By default, a wildcards' bounds are loose (i.e., they allow any subclass or supertype). However, you can tighten the bounds using type erasure. Type erasure replaces your wildcard with the actual type that's closest to it.

For example:

List numbers;

In this case, the ? super Integer wildcards are tightened by replacing them with Object, since Integer is a subclass of Object.

Conclusion

Java's Wildcard system provides a powerful way to work with unknown types. By understanding how to use upper and lower bounds, bounded wildcards, and type erasure, you can write more robust, reusable code that takes advantage of Generics.

Keep in mind that when working with wildcards, it's essential to maintain type safety by being mindful of the allowed types and avoiding ambiguity.

Now go forth and master Java's Wildcard syntax!