Putting test code in a nested class : Nested Classes « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Nested Classes

public class MainClass {
  public MainClass() {
  }

  public void f() {
    System.out.println("f()");
  }

  public static class Tester {
    public static void main(String[] args) {
      MainClass t = new MainClass();
      t.f();
    }
  }
}