Java · Theory

Local Inner class

Theory

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Local Inner class

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

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

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

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

Use Local 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. Local 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 Local 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);
  }
}

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

Short notes

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

Local Inner class

Example

Short notes

Questions

Local Inner class

Example

Short notes

Questions