Advanced Java Topics

This section builds on classes, objects, methods, and collections. Here, Advanced Java is a name for deeper language and runtime topics in this tutorial; it is not a separate Java language or a requirement to use a web framework.

Why Do We Need This?

As programs grow, we may need reusable types, fixed choices, metadata, nested classes, or inspection of classes at runtime. These features solve different problems and should be learned separately.

Main Ideas

Simple Working Example

Run this program on its own. All required imports and classes are included.

class Holder<T> {
    private final T value;
 
    Holder(T value) {
        this.value = value;
    }
 
    T getValue() {
        return value;
    }
}
 
public class HelloWorld {
    public static void main(String[] args) {
        Holder<String> topic = new Holder<>("Generics");
        System.out.println(topic.getValue());
    }
}

Output

Generics

Holder defines a type parameter named T. Using Holder<String> tells the compiler that this holder works with String values. The complete Holder class is included so this program can run by itself.

Topics in This Section

• Reflection API
• Annotations
• Generics
• Inner Classes
• Java Anonymous Class
• Enum
• Wrapper Classes
• Autoboxing & Unboxing

Easy Way to Remember

Use these features to solve a clear problem. More runtime inspection or more complicated type declarations do not automatically improve a design.