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

Java static keyword

Java static keyword Java uses the static keyword for memory management. It can be used along with variables, methods, blocks, nested class. It is used to share the same variable method for the given class. Generally, the main method of a class is labelled as static. To create a member as static, precede its declaration with the keyword static. A static member can be accessed before any objects of its class are created and without reference to any object. When a method declared as static, it cannot call as non-static. Java uses the following members that can be static:

  • Method (class methods)
  • Variable (class variable)
  • Block
  • Nested class
Let’s have a look at below example to understand the concept of static keyword.
public class Demo{
static void method1()
{
System.out.println("This is method1");
}
public static void main(String[] args)
{
method1();
}}
Output
This is method1
Java static methods A method that does not act upon instance variable of the class is known as a static method. A static method is declared with a static keyword. The reason why the static method does not act upon instance variable because the JVM first execute the static method after that, it creates the object. Most used example of the static method is main() method. A static method belongs to the class; it does not belong to the object of the class. A static method can access static data member. It may change the value of static data member. It can be accessed before any object of the class is created. Example With the help of this example, we will understand the use of the static keyword. This is an example of a simple calculation.
Class Calc{ 
     static int cube(inta){ 
     return a*a*a; 
       } 
     public static void main(String args[]){ 
int result=Calc.cube(7);
System.out.println(result); 
  }  }
Output
343
Restrictions for static methods A static method has the following restrictions
  • These methods can only directly call other static methods.
  • These methods can only directly access static data.
  • These methods cannot refer to this or super in any way
Below is an example that demonstrates the restriction of static methods.
public class Demo1
{
static int x=20;  // static variable
int y=40;        //instance variable
static void method1()     // static method
{
x=40;
System.out.println("This is method1");
y=20;    // here it cannot make reference of a static variable
method2();   //cannot make static reference to the non static method
System.out.println(super.a);  // cannot use super
}
void method2()
{
System.out.println("This is method2");
}
public static void main(String[] args)
{
}}
  Why java main() is static? It is necessary for a java program because the JVM calls main() method before any objects are created. So, objects are not required to call a static method. If main() is a non-static method, then JVM  will create an object first, then it will call the main(). It may generate ambiguity and will lead to the problem of extra memory allocation. Java static variable Any variable declared as static is known as a static variable. A static variable is referred to the common property of all objects like company name of the employees, college name of students, etc. it gets memory only once in the class area at class loading time.
  • A static variable can be created at class level only.
  • Static variable and block are executed in the order they are given in the program
  • A static variable is used for fulfilling a common requirement.
  • Static variable allocates memory only once in a class.
  • Static variable makes the program memory efficient.
Syntax-
Public static variableName;
Example-
public class CompanyData
{
int id;
String name;
static String Comp_name="AAA pvt.ltd";
public static void main(String args[])
{
CompanyData c1=new CompanyData();
c1.id=100;
c1.name=" akash shakya ";
System.out.print(c1.id);
System.out.print(c1.name);
System.out.println(CompanyData.Comp_name);
CompanyData c2=new CompanyData();
c2.id=200;
c2.name=" Amritanshu shekhar ";
System.out.print(c2.id);
System.out.print(c2.name);
System.out.print(CompanyData.Comp_name);
            }}
Output-
100 akash shakya AAA pvt.ltd
200 Amritanshu shekhar AAA pvt.ltd
When to Use the static variables and methods? A static variable is used for common property of all objects. Example- in a company all the employee have the same company name. The static method is used for changing static variables. Let’s understand this scenario with below example.
Program

public class CompanyData1

{
            String name;
            int id;
            // static variable
            static String CompName;
            // static counter to set unique roll no
            static int counter = 0;
            public CompanyData1(String name)
            {
                        this.name = name;
                       
                        this.id = setId();
            }
                        static int setId()
            {
                        counter++;
                        return counter;
            }
           
            static void setComp(String name){
                        CompName = name ;
            }
            void getEmployeeInfo(){
                        System.out.println("name : " + this.name);
                        System.out.println("id : " + this.id);
                        System.out.println("compName : " + CompName);
            }

            public static void main(String[] args)
            {
                        CompanyData1.setComp("AAA pvt.ltd");
            CompanyData1 c1 = new CompanyData1("Alok");
                        CompanyData1 c2 = new CompanyData1("Bablu");
                        c1.getEmployeeInfo();
                        c2.getEmployeeInfo();
                       
            }
}
output:
name : Alok
id : 1
compName : AAA pvt.ltd
name : Bablu
id : 2
compName : AAA pvt.ltd
Java static block Static block initializes the static variables. The block is executed at the time of class loading in memory. A class can have more than one static block, and they execute in the same sequence as they are written in the program. JVM executes it before the main(). Till JDK 1.6 it is possible to execute a Java program by static block without main(), but after 1.6, earlier version does not support this feature. Example
class Demo2
{
static {
System.out.println(" This is static block ");
}
public static void main(String args[])
{
     System.out.println("This is main function");}}
Output
This is static block
This is main function
Multiple static blocks As we have discussed before, a java program can have more than one static block. They will execute in the order as they are given in the program. Example for Java multiple blocks is
public class Demo3 {
            static {
                        System.out.println("In static block1");
            }
            static {
                        System.out.println("In static block3");
            }
            static {
                        System.out.println("In static block2");
            }
public static void main(String args[])
{
            System.out.println("In main");
}
}
Output
In static block1
In static block3
In static block2
In main
Static Nested class in Java (Static class)- The top-level class cannot be declared with a static modifier, but nested classes can be declared as static. Such classes are called static class or nested static class. In Java, we cannot make a top-level class as static but can simulate a static class like following steps-
  • Declare the class as final, it prevents extension of the class.
  • Make a constructor private, it prevents instantiation by client code.
  • Make all the functions and members of the class as static.
Example Below is an example of a static nested class.
public class OuterDemo {
static int n=50;
            static class inner{
                        void msg()   
                         {
                         System.out.println("Number is "+n);
                         }
            public static void main(String[] args) {
 OuterDemo.inner obj=new OuterDemo.inner();
obj.msg();
            }}}
Output
Number is 50



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