Question

I’m new to Android(and Java also) and I’m trying to understand what are Fields in predefined Android classes.

For example in the Android View class there are Fileds: EMPTY_STATE_SET, ENABLED_FOCUSED_SELECTED_STATE_SET etc.
Please can you tell me how to understand this and how can I use it? For me it looks like some constants but it’s not.

Answer 1

Typically they are constants for the class, to be used in situations like this:

myWidget.setColor(Widget.BLACK_AND_TAN);

They usually have integer values, but they make the code more readable this way, and also allow for later changes to the API without altering the behavior of previous code. (Widgets.BLACK_AND_TAN == 7, or Widgets.BLACK_AND_TAN ==15,could both be true, or any other number. It doesn’t matter. Just that BLACK_AND_TAN always corresponds to Black and Tan coloring.)

edit: note that Widget is a made up class, as is the BLACK_AND_TAN constant. let me get a real example for you.

Real Example, used to re-position the cursor every time a text field is updated:

DefaultCaret caret = (DefaultCaret)outputArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

Note that these do not HAVE to be constants as we normally refer to them; for example

Toast.LENGTH_LONG;

can be user defined, but it does specify how long a toast should display