Public Object: Java Minutiae - Class.toString()

Java Minutiae - Class.toString()

Class.toString() doesn't return what you'd expect:

  assertEquals("java.lang.Integer", Integer.class.toString());

Instead, it prefixes the fully-qualified classname with "class " for classes, "interface " for interfaces and probably "enum " and "annotation " elsewhere. You need to call getName or getSimpleName() to get what you usually want.

  assertEquals("java.lang.Integer", Integer.class.getName());
  assertEquals("Integer", Integer.class.getSimpleName());

What can I learn from this? The toString() value is important to the usability of an API. With toString, it's often better to be terse rather than complete.

# posted by Jesse Wilson on Thursday, February 28, 2008

You don't need toString in the last two lines, right?

# posted by kirillcool on February 28, 2008 12:27 PM

I never thought too much about this, but perhaps a good toString() guideline is to think "how would this look in a debugger". Because a concise string representation is a lot better than an ugly @ with hex characters.

Or for UI developers, to consider "how would this look if I used it in a list, table or tree", meaning the default toString() should probably return a concise, simple value.

# posted by Eric Burke on February 28, 2008 1:11 PM

Kirill - fixed.

Eric - "How would this look in a table" is a great rule of thumb. I'm going to remember that.

# posted by swankjesse on February 28, 2008 4:50 PM