Java · Theory

Anonymous Inner class

Theory

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Anonymous Inner class

Anonymous Inner class: inner/nested classes live inside another class. Anonymous Inner class is useful for helpers tightly coupled to the outer type.

Anonymous Inner class — anonymous class = one-off implementation.

Anonymous Inner class — static nested class does not need outer instance.

Write one tiny example for Anonymous Inner class. Compile, print one result, and say the output out loud before you type.

Use Anonymous Inner class only when the problem needs it. Don’t force it into every program. Know one beginner trap.

Let's take this on the board with one tiny Main class — no extra files. Anonymous Inner class — static nested Pair groups two ints with the outer Main type. Start from main, go line by line, and stop at each print. That output is the proof for Anonymous Inner class.

Exam tip

Give one real use: event listener / Comparator.

Example

public class Main {
  static class Pair {
    final int a, b;
    Pair(int a, int b) { this.a = a; this.b = b; }
  }
  public static void main(String[] args) {
    Pair p = new Pair(2, 3);
    System.out.println(p.a + p.b);
  }
}

Anonymous Inner class — static nested Pair groups two ints with the outer Main type.

Short notes

DefAnonymous Inner class is a Java idea you should explain with one small example.
RuleKnow the keyword / API used for Anonymous Inner class. Type a tiny Main and print one result.
RememberFor Anonymous Inner class, say the output before you code.
TrapAnonymous Inner class — only memorising the heading. No example, no trap.
Class inside class
Helper cohesion

public class Main { static class Pair { final int a, b; Pair(int a, int b) { this.a = a; this.b = b; } } public static void main(String[] args) { Pair p = new Pair(2, 3); System.out.println(p.a + p.b); } }

Anonymous Inner class

Example

Short notes

Questions

Anonymous Inner class

Example

Short notes

Questions