| Lecture
3A Value vs Reference Overloading Inheritance Overriding OverrideVsOverload InheritanceExample This's & Super's AnotherExample Abstraction Static Meth & Var. |
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| Static Variables & Methods |
In place of global variables as in C/C++, Java allows variables in a class to be declared static:
public
class A {
static int k_var;
....
}
A single memory location is assigned to this variable and it exists and is accessible even when no instances of class_A are created.
These static variable is also called class variables, since they belong to the class as a whole.
If a class property is also declared final, then it becomes a global constant (i.e. can't be altered):
public
class A {
final static int k_var;
....
}
This is how the pi value Math.PI is created in the Math class.
Similarly, methods can also be declared static, and are called class methods
public
class A {
static void A_method(float x){...}
....
}
These class methods also can be called even when no instance of the class exists. The code in a class method can only refer to static variables and the argument variables.
The Math class that we have used, for example, contains static methods to carry out various mathematical functions without having to create a Math object.
public
class mathExample {
static double pi=3.14;
double b=3;
double func(double x){
return ( 4.0*Math.sin(x)**2);
}
static double sfunc(double x){
return (3.0*x);
}
static double tfunc(double x){
return (3.0*x*pi);
}
static double wfunc(double x){
return (3.0*x*b);=>
Error!
Cannot use nonstatic
variable in a class
method.
}
}
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