class methods

As we know instance methods are associated with an object, where as class methods are associated with class.

Syntax

    static dataType methodName(parameters){

    }

Example

    static int getNoOfEmployees(){

    }

Class methods also called as static methods. Static methods called with class name.

Syntax to call class Methods

ClassName.methodName();

Example

class Person{
 static private int count =0;
 
 Person(){
  count++;
 }

 static int getNoOfPersons(){
  return count;
 }
}

class PersonTest{
 public static void main(String args[]){
  Person personA = new Person();
  Person personB = new Person();
  System.out.println("Number Of persons created are " + Person.getNoOfPersons());
 }
}

Output  

Number Of persons created are 2

Some Points To Remember

1. You can't call instance method from static method.

     Example

class Person{
 static int getNoOfPersons(){ 
  setName("HI");
  return 1;
 }
 
 void setName(String s){
 
 }
}

When you try to compile the above program, compiler throws below error

Person.java:4: error: non-static method setName(String) cannot be referenced from a static context
setName("HI");
^
1 error

2. Static methods can't access instance variables

    Example

class Person{
 String name;
 
 static int getNoOfPersons(){
  name="Hi";
  return 1;
 }
}

When you try to compile the above program, compiler throws below error

Person.java:5: error: non-static variable name cannot be referenced from a static context
name="Hi";
^
1 error

3. Applying static for top level class is wrong in java

    Example

static class Person{
 
}

When you try to compile, compiler throws the below error

Person.java:1: error: modifier static not allowed here
static class Person{
^
1 error

4. Static fields are initialized at the time of class loading, where as instance variables are initialized at the time of object creation

5. Just like instance methods, we can overload static methods also

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