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

Constructor in Java with Example

Java Constructor  The constructor is used for object initialization. It's a block of code that initializes a newly created object. It contains a collection of statements that are executed at the time of object creation. The constructor is not mandatory for a programmer to write it for a class, but for the ease of program and security purpose, we make constructors. If the user does not define any constructor for a class, compiler initializes member variables to its default values.

Rules for creating a Java constructor

Some rules for creating a Java constructor are as follows
  • A constructor name should be same as the class name.
  • A constructor should not return a value (not even void).
  • A constructor should not be abstract, final, static, and synchronize.
  • A constructor can use the access modifier in constructor declaration to control its access.
Example
publicclassDemo{
//This is the constructor
Demo()
{
   }
   ..
}
After a Constructor is created, now a question arises that how it works? The answer is when an object is created using new keyword; then a constructor is invoked for initializing the newly created object.
Demo obj= new Demo()
Here the new keyword creates the object of the class Demo and invokes the constructor to initialize the object of Demo class. Example
publicclass Hello {
   String name;
//Constructor
Hello(){
this.name = "Java Constructor.";
   }
publicstaticvoid main(String[] args) {
      Hello obj = newHello();
System.out.println(obj.name);
   }
}
Output
Java Constructor.

Types of constructors

There are three types of constructors.
  • Default constructor
  • Parameterized constructor
  • No-argument constructor
Default constructor Java uses a constructor by default to initialize the object of the class. If you do not write any constructor in Java program, Java compiler inserts a Default constructor in your Java program. Default constructor provides the default values to the objects depending on their type. See the below figure for understanding how a default constructor act. As you can see in the given figure, there is a user made .java file,Java compiler compiles the code and converts it into .class file and creates a constructor for the given class.

Parameterized constructor

A constructor that can have arguments or parameters is known as parameterized constructor. These parameters are used to initialize attributes. Example1
publicclassExDemo{
intx;
publicExDemo(inty) {
x = y;
  }   
publicstaticvoid main(String[] args) {
ExDemoObj = newExDemo(5);
System.out.println(Obj.x);
  }}
Output
5
You can pass more than one parameters in a constructor. Example2
 publicclass Employee {
intempId; 
   String empName; 
//parameterized constructor with two parameters
Employee(intid, String name){ 
this.empId = id; 
this.empName = name; 
   } 
void detail(){
System.out.println("Name: "+empName+" id: "+empId);
   } 
     publicstaticvoid main(String args[]){ 
     Employee e1 = newEmployee(12527,"Vijay"); 
     Employee e2 = newEmployee(12528,"Vikram"); 
     e1.detail(); 
     e2.detail(); 
   } 
}
Output
Name: Vijay id: 12527
Name: Vikram id: 12528
No-argument constructor A constructor that has no parameter or arguments is called as No-argument constructor. Signature of No-argument constructor is the same as default constructor; however, the body can have any code, unlike default constructor. If you write a constructor with arguments or no-arguments, then the compiler does not create a default constructor. Example
class ExDemo1
{
public ExDemo1()
     {
System.out.println("In No-arg constructor");
     }
publicstaticvoid main(String args[]) {
     new ExDemo1();
     }
}
Output
In No-arg constructor

Constructor overloading

Constructors allow overloading as methods do. Constructor overloading is a technique in Java that allows a class can have any number of the constructor, but each constructor should be different in the parameter list. Compiler differentiates constructors based on the number of parameters and their types. Let's have a look at the below example Example
class Student
    {
intRoll_no;
        String SName;
doubleMarks;
Student(intR,StringN,doubleM)        //Constructor 1
        {
Roll_no = R;
SName = N;
Marks = M;
        }
Student(String N,doubleM,intR)        //Constructor 2
        {
Roll_no = R;
SName = N;
Marks = M;
        }
void Display()
        {
System.out.print("\n\t" + Roll_no+"\t" + SName+"\t" + Marks);
        }
publicstaticvoid main(String[] args)
        {
            Student S1 = newStudent(1,"akash mishra",85.57);  // Statement 2
            Student S2 = newStudent(2,"vaibhav Saxena",87.65);  // Statement 1
System.out.print("\n\tRoll_no\tSName\tMarks\n");
S1.Display();
S2.Display();
        }
        }
Output
    Rollno      SName           Marks
     1         akashmishra      85.57
     2         vaibhavSaxena    87.65
Constructor chaining Constructor chaining is a technique of calling one constructor from another constructor concerning current object. You can pass the parameters through a bunch of different constructors.You can maintain your initializations from a single location. Constructor chaining can be applied in two ways
  • Within same class
  • From base class
Constructor chaining within the same class can be done using the this() keyword of the constructor of the same class. Constructor chaining from the base class can be done using the super() keyword that calls the constructor from the base class.

Constructor chaining within the same class using this()

  • this() should always be the first statement of the constructor for constructor chaining.
  • Constructors can be in any order for constructor chaining; it is not necessary to put them in order.
  • At least one constructor should be without this() keyword.
class ExDemo2
{
ExDemo2()
     { 
          this(11);
          System.out.println(" Default constructor");
     } 
     ExDemo2(intx)
     {
          this(10, 12);
          System.out.println(x);
     }
     ExDemo2(intx, inty)
     {
          System.out.println(x * y);
     }
publicstaticvoid main(String args[])
     {
     new ExDemo2();
     }
}
Output
120
11
Default constructor

Constructor chaining from base class usingsuper()
class ExDemo3
{
     String name;
     ExDemo3()
     {
          this("");
          System.out.println("This is No-argument constructor");
     }
     ExDemo3(String name)
     {
          this.name = name;
          System.out.println("This is parameterized constructor");
     }
}

class Child extends ExDemo3
{
     // constructor 3
     Child()
     {
          System.out.println("This is No-argument constructor " +
                             "of child class");     } 
     Child(String name)
     {  
          super(name);
          System.out.println("This is  parameterized " +
                             "constructor of Child class");
     }
     publicstaticvoid main(String args[])
     {
          Child obj = newChild("ExDemo3"); 
     }
}
Output
This is parameterized constructor
This is parameterized constructor of Child class
super() should be the first line of the constructor as super class constructor are invoked before the subclass constructor.

Java copy constructor

By default, Java does not support any copy constructor, but we can copy the values from one object to other like a copy constructor. Below is an example of copying values from one object to another object using Java constructor. Example                
classEmpl{ 
intid; 
    String name; 
Empl(inti,Stringn){ 
id = i; 
name = n; 
    }  
Empl(Emple){ 
id = e.id; 
name =e.name; 
    } 
void display(){System.out.println(id+" "+name);} 
publicstaticvoid main(String args[]){ 
Emple1 = newEmpl(125,"Raghav"); 
Emple2 = newEmpl(e1); 
e1.display(); 
e2.display(); 
   } 
}
Output
125 Raghav
125 Raghav



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