Difference Betwixt Method Overloading As Well As Overriding Inwards Java?

Method Overloading vs Method Overriding

Though the cite of the method remains same inwards the instance of both method overloading too overriding, principal deviation comes from the fact that method overloading is resolved during compile time, piece method overriding is resolved at runtime. Also rules of overriding or overloading a method are dissimilar inwards Java. For example, a private, static too terminal method cannot live overriding inwards Java but yous tin however overload them. For overriding both cite too signature of the method must rest same, but inwards for overloading method, the signature must live different. Last but non the to the lowest degree deviation betwixt them is that telephone telephone to overloaded methods are resolved using static binding piece the telephone telephone to overridden method is resolved using dynamic binding inwards Java.

By the way, Method overloading too method overriding inwards Java is 2 of import concept inwards Java which allows Java programmer to declare method alongside same cite but dissimilar behavior. Method overloading too method overriding is based on Polymorphism inwards Java.

In instance of method overloading, method alongside same cite co-exists inwards same shape but they must possess got dissimilar method signature, piece inwards instance of method overriding, method alongside same cite is declared inwards derived shape or sub class.Method overloading is resolved using static binding inwards Java at compile fourth dimension piece method overriding is resolved using dynamic binding inwards Java at runtime.

In short, when yous overload a method inwards Java its method signature got changed piece inwards instance of overriding method signature remains same but a method tin solely live overridden inwards sub class. Since Java supports Polymorphism too resolve object at run-time it is capable to telephone telephone overridden method inwards Java.

By the way deviation betwixt method overloading too overriding is besides 1 of the pop Java pattern question too appear inwards almost all levels of Java interviews.

What is method overloading too overriding inwards Java?

In this Java tutorial nosotros volition encounter how Java allows yous to create 2 methods of same cite past times using method overloading too method overriding. We volition besides impact base of operations on how methods are bonded or called past times Compiler too Java Virtual Machine too lastly nosotros volition respond of pop interview questions deviation betwixt method overloading too method overriding inwards Java.

This article is inwards my serial of Java article which discusses nearly Interview e.g. Difference betwixt Synchronized Collection too Concurrent Collection or How to Stop Thread inwards Java. Please allow me know if yous possess got another interview questions too yous are looking respond or argue for that too hither inwards nosotros volition endeavour to abide by too hash out those interview questions.

How to Overload a Method inwards Java

If yous possess got 2 methods alongside same cite inwards 1 Java shape alongside dissimilar method signature than its called overloaded method inwards Java. Generally overloaded method inwards Java has dissimilar develop of arguments to perform something based on dissimilar seat out of input.

You tin besides overload constructor inwards Java, which nosotros volition encounter inwards next illustration of method overloading inwards Java. Binding of overloading method occurs during compile fourth dimension too overloaded calls resolved using static binding. To overload a Java method just changes its signature.

Just recollect inwards fellowship to alter signature yous either demand to alter seat out of argument, type of declaration or fellowship of declaration inwards Java if they are of dissimilar types. Since furnish type is non component subdivision of method signature only changing furnish type volition result inwards duplicate method too yous volition acquire compile fourth dimension mistake inwards Java.

In our illustration of Loan too PersonalLoan class, createLoan method is overloaded. Since yous possess got 2 crateLoan() method alongside 1 takes 1 declaration lender piece other accept 2 declaration both lender too interestRate. Remember yous tin overload static method inwards Java, yous tin besides overload individual too final method inwards Java but yous tin non override them.

How to Override a Method inwards Java

In fellowship to override a Java method, yous demand to create a nipper shape which extends parent. Overridden method inwards Java besides shares same cite equally master copy method inwards Java but tin solely live overridden inwards sub class. Original method has to live defined within interface or base of operations class, which tin live abstract as well. When yous override a method inwards Java its signature remains just same including furnish type. JVM resolves right overridden method based upon object at run-time past times using dynamic binding inwards Java. For illustration inwards our instance when nosotros telephone telephone personalLoan.toString() method fifty-fifty though personalLoan object is of type Loan actual method called would live from PersonalLoan shape because object referenced past times personalLoan variable is of type PersonalLoan(). This is real useful technique to modify behaviour of a business office inwards Java based on dissimilar implementation. equals(), hashcode() too compareTo() methods are classic illustration of overridden methods inwards Java.

Another of import betoken is that yous tin non override static method inwards Java because they are associated alongside Class rather than object too resolved too bonded during compile fourth dimension too that’s the argue yous cannot override principal method inwards Java. Similar to static, individual too terminal methods are besides non overridden inwards Java. By the way, equally component subdivision of overriding best practice, ever use @Override annotation, piece overriding method from an abstract shape or interface.

Rules of Method Overriding inwards Java

Following are rules of method overriding inwards coffee which must live followed piece overriding whatever method. As stated before private, static too final method tin non live overridden inwards Java. 

1. Method signature must live same including furnish type, seat out of method parameters, type of parameters too fellowship of parameters 
2. Overriding method tin non throw higher Exception than master copy or overridden method. agency if master copy method throws IOException than overriding method tin non throw super shape of IOException e.g. Exception but it tin throw whatever sub shape of IOException or only does non throw whatever Exception. This dominion solely applies to checked Exception inwards Java, overridden method is costless to throw whatever unchecked Exception. 
3. Overriding method tin non cut down accessibility of overridden method , agency if master copy or overridden method is world than overriding method tin non arrive protected. 

Difference betwixt Method Overloading vs Overriding inwards Java

Overloading vs Overriding inwards Java is 1 of the popular coffee interview questions at many companies too asked at dissimilar levels of programmers. Here are about of import deviation betwixt overloading too overriding inwards Java. Though It's to a greater extent than of import is to empathise how to role both overloading too overriding, these deviation are adept from interview perspective too gives about basic thought equally well:

1) First too most of import deviation betwixt method overloading too overriding is that, In instance of method overloading inwards Java, signature of method changes piece inwards instance of method overriding it rest same.

2) Second major deviation betwixt method overloading vs overriding inwards Java is that You tin overload method inwards 1 shape but overriding tin solely live done on subclass.

3) You tin non override static, final too private method inwards Java but yous tin overload static, terminal or individual method inwards Java.

4) Overloaded method inwards Java is bonded past times static binding too overridden methods are champaign of report to dynamic binding.

5) Private too terminal method tin besides live non overridden inwards Java.

By the way, yous powerfulness possess got heard nearly "a motion-picture demo is worth to a greater extent than than M words" too this is made truthful past times next image. By looking at the pic yous tin clearly empathise deviation betwixt method overloading too overriding inwards Java. 

Handling Exception piece overloading too overriding method inwards Java

While overriding a method it tin solely throw checked exception declared past times by overridden method or whatever subclass of it, agency if overridden method throws IOExcpetion than overriding method tin throw sub classes of IOExcpetion e.g. FileNotFoundException but non wider exception e.g. Exception or Throwable. This restriction is solely for checked Exception for RuntimeException yous tin throw whatever RuntimeException. Overloaded method inwards Java doesn't possess got such restriction too yous are costless to modify throws clause equally per your need.

Method Overloading too Overriding Example inwards Java

Here is an illustration of both method overloading too method overriding inwards Java. In fellowship to explicate the concept nosotros possess got create 2 classes Loan and PersonalLoan. createLoan() method is overloaded equally it has dissimilar version alongside dissimilar signature, piece toString() method which is master copy declared inwards Object shape is overridden inwards both Loan too PersonalLoan class.

public class OverloadingOverridingTest {      public static void main(String[] args) {          // Example of method overloading inwards Java         Loan cheapLoan = Loan.createLoan("HSBC");         Loan veryCheapLoan = Loan.createLoan("Citibank", 8.5);          // Example of method overriding inwards Java         Loan personalLoan = new PersonalLoan();         personalLoan.toString();     }  }  public class Loan {     private double interestRate;     private String customer;     private String lender;      public static Loan createLoan(String lender) {         Loan loan = new Loan();         loan.lender = lender;         return loan;     }      public static Loan createLoan(String lender, double interestRate) {         Loan loan = new Loan();         loan.lender = lender;         loan.interestRate = interestRate;         return loan;     }      @Override     public String toString() {         return "This is Loan past times Citibank";     }  }  public class PersonalLoan extends Loan {      @Override     public String toString() {         return "This is Personal Loan past times Citibank";     } }

Things to Remember

1) In instance of method overloading method signature gets changed piece inwards instance of overriding signature remains same.

2) Return type is non component subdivision of method signature inwards Java.

3) Overloaded method tin live champaign of report to compile fourth dimension binding but overridden method tin solely live bind at run-time.

4) Both overloaded too overridden method has same cite inwards Java.

5) Static method tin non live overridden inwards Java.

6) Since individual method is besides non visible exterior of class, it tin non live overridden too method binding happens during compile time.

7) From Java v onwards yous tin role tone inwards Java to declare overridden method just similar nosotros did alongside @override. @override tone allows compiler, IDE similar NetBeans and Eclipse to cross verify or banking corporation check if this method is actually overrides super shape method or not.

Covariant Method Overriding inwards Java

One of my reader Rajeev makes an interesting comment nearly 1 alter related to furnish type of overriding method from Java v onwards, which enable to role subtype of furnish type of overridden method. This is actually useful, when master copy method returns a full general type similar java.lang.Object. If yous are overriding clone() method inwards Java too thus yous tin role this characteristic to furnish actual type, instead of returning java.lang.Object too tin salve caller from type-casting cloned object. Here is the actual comment from Rajeev:


Hi Javin,I see your weblog regularly too I institute that yous missed covariant return which is added inwards Java v inwards the instance of method overriding. When a subclass wants to alter the method implementation of an inherited method (an override), the subclass must define a method that matches the inherited version exactly. Or, equally of Java 5, you're allowed to alter the furnish type inwards the overriding method equally long equally the novel furnish type is a subtype of the declared furnish type of the overridden (super class) method. Let's hold off at a covariant furnish inwards action:

class Alpha {     Alpha doStuff(char c) {         return new Alpha();     } }  class Beta extends Alpha {     Beta doStuff(char c) { // legal override inwards Java 1.5         return new Beta();     } }

You tin encounter that Beta shape which is overriding doStuff() method from Alpha shape is returning Beta type too non Alpha type. This volition take type casting on client side. See here to larn to a greater extent than nearly covariant method overriding inwards Java.


AS I said 1 of the adept illustration of this is overriding clone method too using furnish type equally Actual type instead of java.lang.Object, which is suggested past times Joshua Bloch inwards Effective Java equally well. This inwards in-fact 1 of the Java best practices piece implementing clone method inwards Java. By the way don't forget to follow these Java overloading best practices, when doing it inwards your project.

Further Learning
SOLID Principles of Object Oriented Design
Absolute Introduction to Object Oriented Programming inwards Java
Java - Object Oriented Programming [For Absolute Beginners]