Bulletprooof - II

Following my previous post, here is another example for bulletproofing your API (again, I am not saying that you should, just wanted to provide a few concrete examples).

Simple (non bulletproof) version:

public class Resource {
  public enum Mode { READ, WRITE }
  public Resource(String fileName) { ... }
  public void open(Mode m, boolean autoFlush) { ... }
  public char read() { ... }
  public void write(char c) { ... }
}

Legal usage:

Resource res = ... ;
res.open(Resource.Mode.READ, false);
char c = res.read();

Illegal usage:

Resource res = ... ;
res.open(Resource.Mode.READ, false);
res.write('a'); // Runtime error: 
                // Resource was opened for READ

The bulletproofing technique remains the same: introduce new classes to make it possible for the compiler to distinguish between the different variants.

public class Readable {
  public char read() { ... }
}

public class Writable {
  public void write(char c) { ... }
}

public class Resource {
  public Resource(String fileName) { ... }
  public Readable openRead(boolean autoFlush) { ... }
  public Writable openWrite(boolean autoFlush) { ... }
}