public interface ByteBufferFactory{
  static final ByteBufferFactory instance=FactoryImpl.valueOf(System.getProperty("ByteBufferFactory", "DIRECT"));
  ByteBuffer newInstance(int capacity);
}

enum FactoryImpl implments ByteBufferFactory{
DIRECT{
  public ByteBuffer newInstance(capacity){
.....
  }
},

HEAP{
 public X newInstance(capacity){
.....
  }
}
}