Java Tutorial

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java BufferedWriter Java InputStreamReader Java File Java Read File Line By Line Java FileOutputStream Jar File in Java

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java

Interface Program in Java

Interface Program in Java

In the previous topic, we discussed that abstraction is possible through the interface and abstract class. An abstract class provides partial to 100% abstraction. 100 %abstraction in abstract class is only possible when every method of the abstract class is abstract. In Java, using interface we can achieve 100% abstraction. It is because an interface only allows abstract methods. A field of an interface is always public, final, and static. Thus, the following code.

 // ABC is an interface
 interface ABC
 {
                int no;
                void print();
 }
 gets converted by the Java compiler into:
 // ABC is an interface
 interface ABC
 {
                public static final int no;
                public abstract void print();
 } 

Observe that keywords like public, static, final, and abstract are implicitly added by the Java compiler. An interface defines a contract that implementing class has to obey. This means an implementing class is bound to define all the abstract methods defined in the interface. This way, an interface ensures the behavior of the implementing class. The interface program in Java shows the importance/ usage of the Java interfaces in the programming world.

Interface and Multiple Inheritance

Unlike classes, Interfaces do support multiple inheritance in Java. This is because, in an interface, only abstract methods are allowed. Consider the following example.

FileName: MultipleInheritanceExample.java

 // interface Parent1
 interface Parent1
 {
     // an abstract method foo()
     void foo();
 }
 // interface Parent2
 interface Parent2
 {
     // an abstract method foo()
     void foo();
 }
 // the class Client implements both the interfaces simultaneously
 class Client implements Parent1, Parent2
 {
     // defining the method foo()
     // access specifier has to be public
     public void foo()
     {
         System.out.println(" In the method foo … ");
     }
 }
 public class MultipleInheritanceExample
 {
     // driver method
     public static void main(String argvs[])
     {
         // creating a client object
         Client obj = new Client();
         obj.foo(); // invoking method foo
     }
 } 

Output:

In the method foo …

Explanation: For interfaces, instead of the keyword extends, keyword implements is used. The class Client implements both the interfaces leading to multiple inheritance. This multiple inheritance never leads to confusion, as the method foo() is not defined in the mentioned interfaces. In classes, multiple inheritance is not supported because methods in the classes are defined, and this definition gives birth to conflict in the inheriting class. One more thing to note here is that except public access specifier, no other access specifier is used in the implementing class. Since all the abstract methods are public in interfaces, the implementing class cannot assign weaker access specifier (rule of inheritance). Therefore, the implementing class is forced to use the public access specifier while defining the abstract methods.

Inheritance in Interfaces

In Java, when a class inherits an interface, it uses the keyword implements (see the above example). However, in case of an interface inheriting another interface, the keyword extends is used. Consider the following example.

FileName: AbstractClassExample.java

 interface findArea
 {
     void area();
 }
 // inteface GeometricalShape inherits the interface findArea
 // Thus, the method area() is also the part of the following interface.
 interface GeometricalShape extends findArea
 {
     void drawShape();
 }
 class Rectangle implements GeometricalShape
 {
     // defining the abstract methods
     public void drawShape()
     {
         System.out.println("Drawing a rectangle");
     }
     public void area()
     {
         System.out.println("Area of a rectangle is l * b");
     }
 }
 public class InterfaceInheritanceExample
 {
     // driver method
     public static void main(String argvs[])
     {
         // creating an object
         Rectangle rect = new Rectangle();
         // invoking methods
         rect.drawShape();
         rect.area();
     }
 } 

Output:

 Drawing a rectangle
 Area of a rectangle is l * b 

Explanation: The interface GeometricalShape is inheriting the interface findArea. Therefore, the implementing class Rectangle, is forced to define the abstract methods declared in the interfaces GeometricalShape and findArea.

Which one is more compatible to use abstract class or interface?

We have seen an abstract class or an interface; both are applicable for achieving abstraction. It automatically leads to the dilemma of choosing between an abstract class or an interface to achieve abstraction. The choice between an abstract class and interface depends on the scenario. For example, in cricket, there are many types of bowlers. One bowler is a spinner, another is medium paced, while others are fast bowlers. However, every bowler has something in common. Those common things are the number of matches played or the total number of wickets taken. Therefore, in such scenarios, the abstract classes are the better choice than interfaces. All the common features can be defined in an abstract class (an interface never provides the definition), and unique ones like the type of bowling (spin-bowling, fast bowling, etc.) or action of bowling can be declared as the abstract methods.

Consider another scenario where we have to write a program for allrounders in cricket. Since allrounders can do both things: batting and bowling, this is the example of multiple inheritance because allrounders inherit the features of a batsman as well as bowler, and multiple inheritance is only possible with the interface. Therefore, we have to take the help of interfaces in order to write the programs for allrounders in cricket.



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