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Java Annotations

Theory

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Java Annotations

Annotations is modern Java (5/8 toolkit). Lambdas are short functions: (n) -> print. They implement a functional interface (one abstract method). Streams let you filter/map/collect a list without a manual loop.

For Annotations: generics keep types safe: List<String>. Autoboxing turns int into Integer when needed. varargs is String... args. Optional avoids some null checks — don’t overuse it.

Keep Annotations small. Don’t dump business logic inside forEach. Know one tiny example you can write from memory.

Let's take this on the board with one tiny Main class — no extra files. Java Annotations — output: Meow. @Override is a real annotation — javac checks the signature matches the parent. Start from main, go line by line, and stop at each print. That output is the proof for Annotations.

Exam tip

Explain Java Annotations as: definition → why → one code idea.

Example

class Animal {
  void sound() { System.out.println("Some sound"); }
}
class Cat extends Animal {
  @Override
  void sound() { System.out.println("Meow"); }
}
public class Main {
  public static void main(String[] args) {
    new Cat().sound();
  }
}

Java Annotations — output: Meow. @Override is a real annotation — javac checks the signature matches the parent.

Short notes

DefAnnotations is part of modern Java (generics / Java 8 style).
RuleAnnotations — lambda = (args) -> body on a functional interface.
UseAnnotations — streams filter/map/collect. Generics = List<String>.
TrapAnnotations — huge logic inside lambdas, or forgetting generics.

class Animal { void sound() { System.out.println("Some sound"); } } class Cat extends Animal { @Override void sound() { System.out.println("Meow"); } } public class Main { public static void main(String[] args) { new Cat().sound(); } }

Java Annotations

Example

Short notes

Questions

Java Annotations

Example

Short notes

Questions