Java · Theory

Inner Classes in Java

Theory

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Inner Classes in Java

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

Inner Classes in Java — anonymous class = one-off implementation.

Inner Classes in Java — static nested class does not need outer instance.

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

Use Inner Classes 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. Inner Classes in Java — 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 Inner Classes.

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);
  }
}

Inner Classes in Java — static nested Pair groups two ints with the outer Main type.

Short notes

DefInner Classes is a Java idea you should explain with one small example.
RuleKnow the keyword / API used for Inner Classes. Type a tiny Main and print one result.
RememberFor Inner Classes, say the output before you code.
TrapInner Classes — 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); } }

Inner Classes in Java

Example

Short notes

Questions

Inner Classes in Java

Example

Short notes

Questions