Java · Theory

Java Member Inner class

Theory

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Java Member Inner class

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

Java Member Inner class — anonymous class = one-off implementation.

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

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

Use Member 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. Java Member 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 Member 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);
  }
}

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

Short notes

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

Java Member Inner class

Example

Short notes

Questions

Java Member Inner class

Example

Short notes

Questions