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The keywords extends and implements, both are used to execute the Inheritance concept of Object-Oriented programming, yet, there is a subtle difference between them. This article on extends vs implements in Java will help you understand the major differences between these keywords.
The topics discussed in this article are:
To better understand the difference between extends and implements, you also need to learn and understand the difference between abstract class and interface in Java.
extends Keyword
When a subclass extends another class, it allows the subclass to inherit (ie. reuse) and override code defined in the supertype. In simple terms, using extends keyword, a newly created class (subclass) can inherit the features of an existing class (superclass). Also, it can override the methods defined in a superclass. A class can never extend more than one superclass in Java. Here’s an example program demonstrating abstract class:
package MyPackage;
class A {
String s;
A(String s1)
{
s = s1;
}
void display()
{
System.out.println(s);
}
}
class B extends A {
String l;
B(String s1, String s2)
{
super(s1);
l = s2;
}
void display()
{
super.display();
System.out.println(l);
}
}
class ExtendsExample{
public static void main(String args[]) {
A ob = new B("Welcome", "To Edureka");
ob.display();
}
}Output: Welcome
To Edureka
Explanation: In the above code, you can observe that class B has extended class A, it has access to display() method and has overridden the method display( ) defined in class A. This immense power comes by using the extends keyword.
implements Keyword
When a class implements an interface, it has to provide an implementation of all methods declared inside an interface. If the class doesn’t wish to provide implementation, it can declare itself as an abstract class. Also, an interface can never implement another interface as implementing means defining the methods and interface always have abstract methods so an interface can never implement another interface. Here’s an example program demonstrating abstract class:
package MyPackage;
interface XYZ{
void display(String s);
void show(int i);
}
class Demo implements XYZ{
public void show(int i){
System.out.println("integer value:" +i);
}
public void display(String s){
System.out.println("string value:" +s);
}
}
class ImplementExample {
public static void main(String args[]) {
XYZ d = new Demo();
d.display("TechDifferences");
d.show(2);
}
}
Output:
string value:TechDifferences integer value:2
In the above code, you can observe that the Demo class implements two methods declared in the interface XYZ.
From the above content, you might have noticed the key difference between extends and implements in Java. Now let’s go ahead and list out other differences.
extends vs implements
The table below lists the key differences between the keywords extends and implements.
| Comparison Features | Extends | Implements |
Implementation | A class can inherit another class, or an interface can inherit other interfaces using a keyword extends | A class can implement an interface using keyword implements |
Method | The subclass that extends a superclass may or may not override all the methods in a superclass | The class implementing an interface has to implement all the methods of that interface. |
Class | A class can extend only one superclass. | A class can implement any number of an interface at the same time |
Interface | An interface can extend any number of interfaces | An interface can never implement any other interface |
Well, now you the key differences between extends and implements in Java
This brings us to the end of this extends vs implements in Java article. We went through the major differences between extends and implements keywords. To conclude, both are used to execute the Inheritance concept of Java but in different ways.
Make sure you practice as much as possible and revert your experience.
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