Any name injava program is called as identifiers. It may be a variable name, a method name, a class etc.
NOTE:ALL THE RED WORDS ARE IDENTIFIERS.
1.The following allowed characters can be taken to declare as identifiers.
2. To declare an identifier the first character shouldnot be digit.
4.All inbuilt class & interfaces can be considered as identifier, but it is not recommended because the readability of the code reduce.
Here String is a valid identifier but not recomnded.
Here Runnable(an inbuilt interface) is a valid identifier, but not recommended.
5. There is no length limit of identifier.