Why do variable names often start with the letter 'm'? [duplicate]

It stands for member. I personally find this convention unhelpful, but it's subjective.

See Code Style Guidelines for Contributors: Follow Field Naming Conventions. The use of the "m" prefix is more specific that simply denoting a "member" variable: It's for "non-public, non-static field names."

According to Android source code documentation:

• Non-public, non-static field names start with m.
• Static field names start with s.
• Other fields start with a lower case letter.
• Public static final fields (constants) are ALL_CAPS_WITH_UNDERSCORES.

Note that this is for writing Android source code. For creating Android apps, the Google Java Style Guide may be more helpful.

The m is here to indicate a member variable.

It has 2 huge advantages:

• If you see it, you instantly recognize it as a member variable.
• Press m and you get all members via the auto completer. (This one is not in the other answers)

'm' means member of the class. So, if you don't use IDE to highlight your members, then you will understand that it is a member by it's name