Friday, February 13, 2015
Java Variable Types and Rules for Declaring Variables
Variable is nothing it is just the name of memory location. While declaring variables we must follow rules given below.
Rules for Declaring Variables in Java
1. Variable name must bound with data type. It means while declaring a variable we must specify its data type.
Ex: int x=10;
2. Reserve word or keywords cannot be taken as a variable name.
4. Nothing except 0-9, A-Z, a-z, _, $ can be used in variable name.
5. Variable name must not start with numeric and special characters are also not allowed.
Example:
intabc=7; (valid)
int _abc=8; (valid)
int abc8=9; (valid)
int 8abc=10 (invalid)
int $_abc=12; (valid)
int $_abc*=15; (invalid)
6. Variable name should be meaningful.
Example:
string i=”Raj”; //valid but not meaningful
string name=”Raj”; //valid and meaningful
Note: Local variables must be initialized before first use.
class demo
{
public static void main(String…s)
{
int x; //must be initialized
System.out.println(x);
}
}
Java Variable Types
There are three types of variables in Java that are instance, local and static.
1. Instance Variables
Instance variables are declared in a class, but outside any method, constructor or block.
2. Local Variables
Local variables are declared in methods, constructors or blocks. It must be initialized before first use.
3. Static Variables
Static variables are declared with the static keyword in a class, but outside any method, constructor or block.
class A
{
int x=12; //instance variable
staticint y=13; //static variable
public static void main(String…s)
{
int z=30; //local variable
System.out.println(x);
System.out.println(y);
System.out.println(z);
}
}
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