What Is Overloading and Overriding In OOP? Simple to Begin

Overloading and Overriding in OOP (Object-Oriented Programming ) are frequently used object-oriented programming techniques. Those are used to write and design code clearly and smartly. Design patterns are heavily used overriding when designing the application.

What is Java Overloading?

In a single Java class possible to create methods with the same name but with different parameters. This is called method overloading. When method overloading, the compiler (Compile-time) is able to decide which method runs at runtime.

Method signature change according to the parameters in overloading. Therefore the compiler sees the difference between each method and decides which method to run. That’s called compile-time binding or static binding.

Java Overloading Rules

• Method name should be equal
• Parameter list should be different.
• Return type able to change in overloaded methods
• Access modifiers can change in overloaded methods.
• Exception may vary with overloaded methods

public class Overloading {
   public static void main(String[] args) {
      EasyPlus easyPlus =new EasyPlus();
      System.out.println("2 + 3 = "+easyPlus.plus(2, 3));
      System.out.println("2.5 + 3.5 = "+easyPlus.plus(2.5, 3.5));
      System.out.println("2.5 + 3.5 = "+easyPlus.plus(2.5f, 3.5f));
   }
}
// Created three functions with same name but with different parameters
class EasyPlus{
   public int plus(int a, int b){
      return a+b;
   }
   public double plus(double a, double b){
      return a+b;
   }
   public float plus(float a, float b){
      return a+b;
   }
}

Output

2 + 3 = 5
2.5 + 3.5 = 6.0
2.5 + 3.5 = 6.0

What is Java Overriding?

What Is Polymorphism In Object-Oriented Programming (OOP)? The page describes how polymorphism works. Run time or Dynamic polymorphism is through the inheritance. Inheritance (Look What Is Inheritance In Object-Oriented Programming (OOP)?) Hierarchy subclass methods derive from a parent class and in subclass reimplement parent class method with the same signature is call method overriding.

Which overridden function to run at runtime is decided by JVM. It’s called runtime binding or dynamic binding. The overriding method should have the same signature (same name and same parameter). Reference of the object can be any parent type class of the inheritance hierarchy. But in the run time, JVM runs only the object type method.

Java Overriding Rules

• Method signature must be equal (Name and Parameter List)
• Access modifiers can’t more restrictive. if the parent class method is “public” then Child class is not possible to “default, protected, or private”.
• Return type can be the same type or subtype as the parent class method.
• Overridden methods can throw any new unchecked exception.
• Overridden method can throw narrow or fewer checked exceptions but not throw any broader or wider exceptions than the parent method.
• Overriding only for inherited class methods
• Final methods are not allowed the override
• Static methods are not allowed to override but are able to redeclare.
• Constructors are not overriding.

Java Overriding Examples

public class OverridingEx1 {
   public static void main(String[] args) {
      //Reference class is top of the hierarchy but objects type are child of PrintPaper
      PrintPaper printPaper;
      printPaper =new BlankAndWhite();
      printPaper.print(1);
      printPaper =new Color();
      printPaper.print(1);
      printPaper =new Laser();
      printPaper.print(1);
      // Object in the runtime dicide which method to run
   }  
}
//Define the print method in interface
interface PrintPaper{
   public void print(int paperCount);
}
// Method override for Black and white printing
class BlankAndWhite implements PrintPaper{
   public void print(int paperCount){
         System.out.println("Print Black and White");
   }
}
// Method override for color printing
class Color extends BlankAndWhite{
   public void print(int paperCount){
         System.out.println("Print Color");
   }
}
// Method override for laser color printing
class Laser extends Color{
   public void print(int paperCount){
         System.out.println("Print Laser Color");
   }
}

Output

Print Black and White
Print Color
Print Laser Color

Java Overriding Dynamic Binding Extended

The Second example shows printMyPaper(PrintPaper printPaper) receiving PrintPaper type object as a parameter but we can pass any type of object in the hierarchy. When runtime decides which method in class should be run.  

public class OverridingEx2 {
   public static void main(String[] args) {
      OverridingEx2 overridingEx2 =new OverridingEx2();
      overridingEx2.printMyPaper(new BlankAndWhite());
      overridingEx2.printMyPaper(new Color());
      overridingEx2.printMyPaper(new Laser());
   }  
   // printMyPaper method accept any type of object in Inheritance hierarchy 
   public void printMyPaper(PrintPaper printPaper){   
      // JVM decide which method to run (Runtime Binding)
      printPaper.print(1);
   }
}

Output

Print Black and White
Print Color
Print Laser Color