Static Methods in Java Examples

It is possible to have static methods in a class in the same way as we have static fields. The static method is similar to instance method) of a class but the only difference is that the static method can be called through its class name without creating any object of that class. A static method is also called class method as it is associated with a class and not with individual instance of the class. We have already seen the sqrt () method which is a static method within Java standard Math class. A method is declared static when its behavior is not dependent on the instance variable just like Math.sqrt (4.5).This method never uses instance variables so it does not need to know about the specific object.

There is an important restriction on the static method that it can access only static fields and other static methods of a class. This is because static methods can exist and be used even if no objects of that class have been created. If an attempt is made to access a non-static field from the static method then the compiler will generate an error as the static method does not know which nonstatic field value to use. Similarly, a static method cannot access non-static method either because non-static methods are usually associated with instance variable state.

To understand the concept of static method, let us consider the same example as we discussed with static field. Now let us consider another program. Consider a bank decides to change the rate of interest for all its customers then we need to make a method in the class that update it. This can be illustrated in the following program.

// Program That Maintain Bank Account Information about Various Customers 
 class Account 
 { 
       int accountNo; //account ID 
       double balance ; 
       static double rate = 0.05; 
       void setData(int n,double bai) 
       { 
          accountNo = n ; 
          balance = bai ; 
       } 
       void quarterRatecal() 
       { 
          double interest = balance * rate * 0.25 ; 
          balance += interest ;   
       } 
       static void modifyRate(double incr) 
       { 
          rate += incr; 
          System.out.println("Modified Rate of Interest : " + rate); 
       } 
       void show() 
       {  
          System.out.println("Account Number : " + accountNo); 
          System.out.println("Rate of Interest : " +rate); 
          System.out.println("Balance : "+ balance); 
       } 
 } 
   public class StaticMethod 
   { 
       public static void main(String[] args) 
       {   
         Account acc1 = new Account(); 
         Account acc2 = new Account(); 
         Account.modifyRate(0.01); 
         System.out.println("Customel Information......"); 
         acc1.setData(201,1000); 
         acc1.quarterRatecal();  //Calculate interest 
         acc1.show(); //display account interest 
         System.out.println("Customer2 Information......"); 
         acc1.setData(202,1000); 
         acc2.quarterRatecal(); //Calcuate interest 
         acc2.show(); //display account information 
       } 
   } 
 

The Account class contains a static method modifyRate ().It modifies the rate of interest by the value specified as argument (0.01). The method modifyRate () is made static in the class as we are only using static field rate in it. Only static method can access a static field.

The following points should be remembered while working with static methods.

.  A static method should be called using the class name rather than !in object reference variable.
.  A static method is good for a utility method that does not depend upon a particular instance variable value.
.  A static method can neither access a non-static field nor a non-static method .
. If you have a class with only static methods and you do not want the class to be instantiated, you can mark the constructor private. For example: In the Math class, the constructor is marked private because it contains only static methods.