Advanced Generics Techniques in Java

Introduction

Generics in Java provide a way to define classes, interfaces, and methods with a placeholder for types. This allows for code that is both type-safe and reusable.

Wildcards

Wildcards are represented by the question mark (?) and are used in situations where you want to allow for flexibility in types.

Types of Wildcards

• Unbounded Wildcards: List<?>
• Upper Bounded Wildcards: List<? extends T>
• Lower Bounded Wildcards: List<? super T>

Example

import java.util.Arrays;
import java.util.List;

public class WildcardExample {
    public static void printList(List<? extends Number> list) {
        for (Number number : list) {
            System.out.println(number);
        }
    }

    public static void main(String[] args) {
        List<Integer> intList = Arrays.asList(1, 2, 3);
        printList(intList);
    }
}
                

Bounded Type Parameters

Bounded type parameters restrict the types that can be used as arguments for a generic type. You can specify a single bound or multiple bounds.

Example

public class BoundedTypeExample<T extends Comparable<T>> {
    private T element;

    public BoundedTypeExample(T element) {
        this.element = element;
    }

    public T getElement() {
        return element;
    }
}
                

Generic Methods

Generic methods allow the definition of methods with their own type parameters, which can be different from the containing class's type parameters.

Example

public class GenericMethodExample {
    public static <T> void printArray(T[] array) {
        for (T element : array) {
            System.out.println(element);
        }
    }

    public static void main(String[] args) {
        Integer[] intArray = {1, 2, 3};
        printArray(intArray);
    }
}
                

Type Erasure

Type erasure is a process by which the Java compiler removes all generic type information during compilation. This ensures that Java remains backward-compatible with older versions.

Implications

• Generics do not exist at runtime.
• Type casts are required when dealing with raw types.

Best Practices

Here are some best practices for using generics effectively:

• Use generics to eliminate the need for casting.
• Prefer using bounded wildcards when working with collections.
• Avoid using raw types, as they negate the benefits of generics.
• Use generic methods for code reusability.

FAQ