Method overriding in java

If a subclass provides a method with the same signature (name and parameter) as in its super class, then subclass overrides the method of its super class. This process of overriding a super class method by subclass is known as method overriding.

Conditions for method overriding:

Method in subclass must have same signature as in its super class.
Two classes must follow IS-A relationship.

Example:

/**
 * This program is used for simple method overriding example.
 * @author W3spoint
 */
class Student {
      /**
       * This method is used to show details of a student.
       * @author W3spoint
       */
      public void show(){
            System.out.println("Student details.");
      }
}
 
public class CollegeStudent extends Student {
      /**
       * This method is used to show details of a college student.
       * @author W3spoint
       */
      public void show(){
            System.out.println("College Student details.");
      }
 
      //main method
      public static void main(String args[]){
       CollegeStudent obj = new CollegeStudent();
       //subclass overrides super class method
       //hence method of CollegeStudent class will be called.
       obj.show();
      }
}

Output:

College Student details.

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Can static method be overridden?

No, Static methods can’t be overridden because they are associated with class not with the object.

Role of access modifiers in method overriding:

Access modifier of overridden method in subclass can’t be more restrictive than in super class. Otherwise it will throw an exception.

Example:

/**
 * This program is used for simple method overriding example.
 * @author W3spoint
 */
class Student {
      /**
       * This method is used to show details of a student.
       * @author W3spoint
       */
      public void show(){
            System.out.println("Student details.");
      }
}
 
public class CollegeStudant extends Student {
      /**
       * This method is used to show details of a college student.
       * @author W3spoint
       */
      protected void show(){//compile-time error
            System.out.println("College Student details.");
      }
 
      //main method
      public static void main(String args[]){
       CollegeStudant obj = new CollegeStudant();
       //subclass overrides super class method
       //hence method of CollegeStudant class will be called.
       obj.show();
      }
}

Output:

Exception in thread "main" java.lang.Error: 
Unresolved compilation problem:
Cannot reduce the visibility of the inherited method from Student
at com.w3spoint.business.CollegeStudent.show(CollegeStudent.java:22)
at com.w3spoint.business.CollegeStudent.main(CollegeStudent.java:30)

Download this example.

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