Generic classes in Java provide a powerful way to create flexible, type-safe code that works with different data types. They allow you to write classes that can operate on objects of various types while maintaining compile-time type safety.

What are Generic Classes?

Generic classes are classes that are parameterized over types. They enable you to define a class with a placeholder for the type of data it can work with. This placeholder is called a type parameter.

Syntax of Generic Classes

To create a generic class, use angle brackets <> after the class name and specify one or more type parameters. Here's the basic syntax:

public class ClassName<T> {
    // Class body
}

In this syntax, T is a type parameter that can be replaced with any valid Java type when the class is instantiated.

Benefits of Generic Classes

Type safety: Catch type errors at compile-time rather than runtime
Code reusability: Write once, use with multiple types
Elimination of type casting: Reduce explicit casts in your code
Implementation of generic algorithms: Create methods that work with different types

Example: Generic Box Class

Let's create a simple generic class that can hold any type of object:

public class Box<T> {
    private T content;

    public void set(T content) {
        this.content = content;
    }

    public T get() {
        return content;
    }
}

Now you can use this Box class with different types:

Box<Integer> intBox = new Box<>();
intBox.set(10);
int value = intBox.get();

Box<String> stringBox = new Box<>();
stringBox.set("Hello, Generics!");
String message = stringBox.get();

Multiple Type Parameters

Generic classes can have multiple type parameters. This is useful when you need to work with more than one type in your class:

public class Pair<K, V> {
    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() { return key; }
    public V getValue() { return value; }
}

Type Bounds

You can restrict the types that can be used with your generic class by using bounds. For example, to create a class that works only with numbers:

public class NumberBox<T extends Number> {
    private T number;

    public void set(T number) {
        this.number = number;
    }

    public double getDoubleValue() {
        return number.doubleValue();
    }
}

This NumberBox class can only be used with types that extend Number, such as Integer, Double, or Float.

Best Practices

Use meaningful names for type parameters (e.g., T for type, E for element, K for key, V for value)
Consider using bounds to restrict type parameters when necessary
Be aware of type erasure and its implications in Java generics
Use the diamond operator <> for brevity when instantiating generic classes in Java 7 and later

Related Concepts

To deepen your understanding of generics in Java, explore these related topics:

Generic classes are a fundamental part of Java's type system, enabling developers to write more flexible and robust code. By mastering generic classes, you'll be able to create reusable components that work seamlessly with various data types while maintaining type safety.