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Java Nested Interface

Theory

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Java Nested Interface

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

Java Nested Interface — anonymous class = one-off implementation.

Java Nested Interface — static nested class does not need outer instance.

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

Use Nested Interface 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 Nested Interface — 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 Nested Interface.

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 Nested Interface — static nested Pair groups two ints with the outer Main type.

Short notes

DefNested Interface is a Java idea you should explain with one small example.
RuleKnow the keyword / API used for Nested Interface. Type a tiny Main and print one result.
RememberFor Nested Interface, say the output before you code.
TrapNested Interface — 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 Nested Interface

Example

Short notes

Questions

Java Nested Interface

Example

Short notes

Questions