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 Program to find and replace characters on string in java Program to find the duplicate characters in a string Program to check whether a given character is present in a string or not Java Program to Print Permutations of String Java program to find frequency of characters in a string Java Program to remove duplicate characters in a string

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 Methods 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 file Reader Java Buffer Reader Java file Writer Java BufferedWriter Java InputStreamReader Scanner in Java Java StringReader Java StringReader Class Java PrintWriter Java File Java Read File Line By Line Java FileInputStream Java FileOutputStream Java Create File Java Delete File Java Open File Java Read File to String Java copy file Java Read JSON file Jar File in Java Java FileNotFoundException

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 JDBC Architecture Types of JDBC Drivers JDBC vs ODBC Java Database Connectivity with MySQL Statements in java Prepared statement in Java Resultset in java Java ResultSetMetaData DatabaseMetaData in Java Callable Statement in Java Transaction Management in java

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 add double quotes in a string in Java How to convert list to String in Java 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 find the length of an Array 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 import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction in Java How to call static method in Java How to compare characters in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String 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 Array and String based questions in Java Array and String with Examples in Java Best Practices to use String Class in Java What is string in Java why it's immutable Java String Java String Inbuilt functions Java String Matches vs Contains Sum of digits in string in java Check the presence of Substring in a String in java Java import packages Interfaces and Classes in Strings in Java Maximum length of string in java Hidden classes in Java Class memory in Java public static void main string args meaning in java Reverse a String in Java String Concatenation in Java Difference between String and Char Array in Java Buffer reader to read string in Java Split String into String Array in Java Reverse a String using Collections in Java

Objects and Classes in Java

Objects and Classes in Java

Classes and objects are the basic concepts of object-oriented programming. It revolves around the real world entity. In Java, the object is a physical and logical entity, whereas classes are logical entity only.

Objects in Java-

Objects are real-world entities that have state and behavior. Objects can be physical and logical. It is the instance of the class. Some example of objects are-

table, fan, chair, car, train, etc.

We can say objects are-

  • Real-world entities
  • Instances of the classes
  • Tangible or intangible
  • Entities which have state and behavior

Objects can be tangible or intangible both. The banking system is the example of the intangible object. Object corresponds to things found in the real world.

Every object has some characteristics like its name, method, and other information about it. Characteristics of an object are-

  • State
  • Behavior
  • identity

State- it contains the attribute and value of an object. It is the reflection of object properties.

Behavior- it contains methods of an object. It is the response reflection of an object to another object. It represents the functionality of an object like deposit, etc.

Identity- identity is a unique id. It is used internally by the JVM to identify the uniqueness of the object.

Example of an object

Object Car

Identity- 

Object name- car

Attributes-

Brand

Model

Color

speed

Behavior-

Run

Speed

Object declaration-

As an object is called an instance of the class so, when an object is created in a class, class is said to be instantiated. All the instances share the attributes and properties of the class, but the values of these attributes (state) are unique. A single class can have any number of instances.

Example-

public class Car
{
String brand;
String model;  //instance variable
int speed;
public Car(String brand, String model, int speed)
{
this.brand=brand;
this.model=model;
this.speed=speed;
}
public String getBrand()
{
return brand;
}
public String getModel()
{
return model;
}
public int getSpeed()
{
return speed;
}
public String method()
{
return("my cars brand is" +this.getBrand()+"\n my model is  " +this.getModel()
+ "my speed is " +this.getSpeed());
}
public static void main(String[] args)
{
Car c1=new Car(" toyota", "camery" ,250);
System.out.println(c1.method());
}}

Output-

my cars brand is Toyota
my model is  camery my speed is 250

Ways to create an object of a class-

  • Using a new keyword
  • Using class.forName(String  className) method
  • Using clone() method
  • Deserialization

Using new keyword-

It is most common and used way to create object in java.

Demo obj= new Demo()

Using Class.forName(String className) method-

In JAVA, there is a predefined class Class in java.lang package. The forName() method is a Java Class method. This method returns the class object associated with the class or interfaces with the given name in the parameter as String.

Demo obj=(Demo)Class.forName(“pack1.Demo”).newInstance();

Consider class Demo present in pack1 package.

Using clone() method-

clone() method is an Object class method. This method creates and returns a copy of the object class.

Demo obj=(Demo)obj.clone();

Using Deserialization-

Deserialization is a process of reading an object from a saved file.

FileInputStream file=new FileInputStream(filename);
ObjectInputStream in=newObjectInputStream(file);
Object obj=in.readObject();

Classes in java-

Classes are the user-defined blueprint of objects. It contains a set of properties and method that are common to all objects of one type.

We use the keyword class for creating a class.

Syntax-

class ClassName
{
Methods
Fields
…….
…….
}

A Java class contains-

  • Methods
  • Fields
  • Constructors
  • Blocks
  • Nested classes and interfaces

Methods in Java-

In Java, a method is a block of code meant for any certain operation. It runs when it calls. Methods can be called anywhere in the program. Methods are like functions.

Advantages-

Code re-usability is the main advantage of methods we can use the code many times by defining only once.

Code optimization is also an advantage of methods. We can reduce the line of code of a program by defining methods.

To create a method-

Methods should be defined within the class. It should be determined by method name followed by parenthesis (). There are some predefined methods in java, like System.out.println(). An example of creating method is below.

public class Demo{
  static void method1() {
    // code to be executed
  }
}

In the given example we have defined method ‘method1’ within the demo class.

To call a method-

To call a method write method name followed by parenthesis () and thereafter semicolon ‘; ‘.  Like in the below program, I defined method1 for printing “in method 1”. When I will call the method1() it will give the output as “in method 1”.

public class Demo{
  static void method1() {
    System.out.println("in method 1");
  }
  public static void main(String[] args) {
    method1();
  }
}

Output-

In method 1

Fields-

A class field may contain many things like variables constant and other data types.

A class contains any of the following variables-

  • Local variables
  • Class variable
  • Instance variable

Local variable-

Local variables are defined within the methods, constructor, or blocks. These variables are initialized within the block and destroyed when the method is completed. 

Class variable-

Class variables are defined within the class outside any methods with the static keyword.

Instance variable-

An instance variable is defined within the class outside any methods. These variables are initialized when the class is initialized. Instance variable can be accessed anywhere in the program.

Constructors-

One of the most important subtopics of the class is a constructor. Every class contains a minimum of one constructor. If we do not define it manually, then Java compiler will create a constructor by default.

When a new object is initialized, a constructor is invoked. It initializes the objects. Its name is as class name. More than one constructor can be created in a single class.

Let's have a look at the below example-

public class  Student
{
public Student()
{
…….// initializing objects
…….
}}

Block in Java-

A block contains one or more statements enclosed in braces. Generally, a block is used to group several statements so that they can be used on the requirement.

Below is an example of a simple block.

{ //block start
        int a = 50;
        a++;
} //block end

Java example for objects and classes-

Example1-

This is a simple example for how to define class and fields.

class Shop{ 
//fields 
float mrp;/instance variable 
String name; 
//main method 
public static void main(String args[]){  
  Shop s1=new Shop();//creating an object of Shop 
  //Printing values
  System.out.println(s1.mrp);//accessing member variable
  System.out.println(s1.name); 
} 
}

Output-

0.0
null

Example2-

For initialization through reference variable-

Initialization means storing the data into a variable. In this example, we will store the value into an object through the reference variable.

class Shop1{ 
int mrp; 
String name; 
public static void main(String args[]){ 
  Shop1 s1=new Shop1(); 
  s1.mrp=24575; 
  s1.name="Samsung LED"; 
  System.out.println(s1.mrp+" "+s1.name);
} 
}

Output-

24575 Samsung LED

Example3-

Initialization through method-

In this example, we will create two objects of the Shop class and initializing the value of these objects through methods.

class Shop2{ 
float mrp; 
String name; 
void record(int m, String n){ 
  mrp=m; 
  name=n; 
} 
void display(){System.out.println(mrp+" "+name);} 
public static void main(String args[]){ 
  Shop2 s1=new Shop2(); 
  Shop2 s2=new Shop2(); 
  s1.record(24575,"Samsung LED"); 
  s2.record(22000,"MI Smart TV"); 
  s1.display(); 
  s2.display(); 
} 
}

Output-

24575.0 Samsung LED
22000.0 MI Smart TV



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