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

Abstract classes in Java

Abstract classes in Java Java uses the 'abstract’ keyword to make a class abstract. Such classes are known as abstract classes, and the process is known as abstraction. In programming language, abstract classes are generic classes (or types of objects) used as a basis to create particular objects that conform to its protocol, or the set of operations it supports. Some important points regarding abstract classes

  • An Abstract class is a class that contains abstract as well as concrete methods.
  • An Abstract class can't be instantiated in other words. We cannot create the object of an abstract class.
  • An abstract class is a class that has at least one abstract method, and maybe there can be some regular methods.
  • An abstract class can have static methods and constructors.
  • An abstract class can have final methods which will prevent the subclass from changing the body of the method.
  • We can achieve 0 to 100 percent abstraction using Java abstract classes.
In an object-oriented programming language, classes contain the objects, attributes (properties) and behaviors (methods) which can be based on previously defined classes. Java uses inheritance to derive the specific implementation of abstract classes. When this principle applied for many successions, it creates a hierarchy of classes.  In this situation, abstract classes are at the top and are used to enforce methods that need to be overridden in the subclasses. This process avoids potential runtime errors.

Declaration of abstract class

abstract class Demo
{
abstract method1();
void method2();{
}}

Rules for abstract class

Here are some points that should be remembered before you make an abstract class. We can call them as rules
  • To use an abstract class, we have to inherit it from the other class.
  • To use an abstract class, you need to create another class which extends this class.
  • A class derived from a parent abstract class must contain all the methods of the parent class.
  • The object of the abstract class cannot be created.
  • If the child class does not contain all the method of a parent class, then it should be declared as an abstract class.

Why we need an abstract class?

Let's assume a Student class that contains method info() and its subclasses, name, id etc.. Since every name contains a different id like 'a' contain id 111 and 'b' contains id 222, so there is no point to implement this method to parent class because every child class overrides the method to provide its implementation detail. So when we know that all the student classes will override this, then there is no point to implement this method in the parent class. Thus making this method abstract is a good option. By making this method abstract, we force all the child classes to implement this.

Abstract methods

An abstract method is a method that has only the method definition. An abstract method does not have implementation and body. It defines only the signature of the method. Syntax  abstract void method(double X, double Y); If a class contains at least one abstract method, then it should be declared as abstract. public abstract class Demo{   // declare fields   // declare nonabstract methods   abstract void method();} If an abstract class is subclassed, then subclass will provide the implementation for all abstract method of the parent class. However, if it will not provide the implementation then the subclass must be declared as abstract.

Some scenarios of Abstract class

Example 1
abstract class Food{ 
abstract void eat(); 
} 
//in abstraction, implementation is unknown by end user 
class Pizza extends Food{ 
void eat(){System.out.println("Pizza is fantastic");} 
} 
class Burger extends Food{ 
void eat(){System.out.println("Burger is delicious");} 
} 
//In abstraction, method is called by programmer or user 
class TestAbstraction{ 
public static void main(String args[]){ 
Food obj=new Burger();//In Abstraction, object is provided through method 
obj.eat(); 
} 
} 
Output
Burger is delicious
In the given example, Food is the abstract class and its implementation is provided by the Pizza and Burger classes. Mostly, implementation detail is hidden for us (which is hidden to the end user), and an implementation class object is provided by the factory method. Example 2 This example explains that a Java program may contain an abstract class, an abstract method, method body (non-abstract method), data member, constructor, and even main() method. Have a look at the below example.
abstract class Pc{ 
        Pc(){System.out.println("PC repaired successfully");
        } 
        abstract void performance(); 
        void changeOS(){
     System.out.println("Win 10 installation is successful");
       } 
      } 
     //Creating a Child class which inherits Abstract class 
      class Hp extends Pc{ 
      void performance(){System.out.println("performance is Superb..");} 
      } 
     //Creating a Test class which calls abstract and non-abstract methods 
      class TestAbstraction1{ 
      public static void main(String args[]){ 
       Pc obj = new Hp(); 
       obj.performance(); 
       obj.changeOS(); 
      } 
     }
Output
PC repaired successfully
Performance is Superb..
Win 10 installation is successful



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