The different types of variables in a Java

The different types of variables in a Java program

Different types of information • Computer program needs information to operate correctly The information used by computer programs are stored inside variables • We can divide the information broadly into: • Short term information • Long(er) term information • As a result, computer programs use different kinds of variables specialized to store short term and long term information

Different types of information (cont. ) • Furthermore, because variables can take up a lot of RAM memory, we organize the storage of the different kinds of variable in the RAM memory.

The different types of variables in the Java program • Java has 4 different kinds of variables (See: http: //download. oracle. com/javase/tutorial/java/nutsandbol ts/variables. html) • Class variables • Instance variables • Local variables • Parameter variables

The different types of variables in the Java program (cont. ) • General information on variables: • Each type of variable has it's own characteristics (properties) • The type of variable is determined by: • Where the variable is defined • Whether the keyword static was used in the variable definition.

Properties of variables • Every variable has 2 properties: • life time = the duration that a variable exists • scope = the region in the program where the variable is accessible (can be used)

Properties of variables (cont. ) • Note: • The different kinds of variables (class, instance, local and parameter variables) have different life time durations and different scopes

Why do programs have different kinds of variables • The reason is to accommodate different needs: • Short term information: Some information need only be retained within a (one) method (We call this kind of information local information) • Long term information: • Some information must be retained across several methods

Why do programs have different kinds of variables (cont. ) • Local variables and parameter variables are used to store local (or short term) information • Class variables and instance variables are used to store longer term information