Java Factory example

A.java

class A {
  public static void main(String[] Args) {
    A a = new A(new B1Factory());
    System.out.println(a);
    
    a = new A(new B2Factory());
    System.out.println(a);
  }
  
  private BFactory factory;
  public A(BFactory factory) { this.factory = factory; }
  public String toString() { 
    return "<A containing the b: " + factory.b() + ">";
  }
  
  static interface BFactory {
    public B b();
  }
  
  static interface B {
    public String toString();
  }
  
  static class B1Factory implements BFactory {
    public B b() { return new B1(); }
  }
  static class B1 implements B {
    public String toString() { return "b1"; }
  }
  
  static class B2Factory implements BFactory {
    public B b() { return new B2(); }
  }
  static class B2 implements B {
    public String toString() { return "b2"; }
  }
}