Keywords –
- Keywords are reserved words or predefined words that you cannot use as a variable or object name. In addition, they have special meaning for the compiler.
- True, false, and null are not reserved words; however, you cannot use it as identifiers, because it is literals of built-in types.
- Some of the examples include abstract, boolean, break, extend, public, return, etc.
Identifier –
- An identifier is a string of alphanumeric characters (a-z , A-Z , 0-9) (i.e. letters & digits) and underscore( _ ) symbol.
- It is a token (in other words, a symbol) that name language entities; for instance, constants, variables, structures, functions, etc.
- Identifier names must be unique and must not contain white spaces.
- The first character should be an alphabet or an underscore.
- You cannot use a keyword as identifiers.
- Identifiers are case-sensitive.
Variables –
- A variable is a container that holds the value while the program it executes. The program can change the value stored in a variable during program execution.
- Every variable has a specific type, which determines the following –
- Size of its memory
- The range of values that it can store
- The set of operations that it can apply to the variable.
- Examples include (with & without assignment) –
- int total;
- int total = 50;