Java provides various datatypes to store various data values. It provides 7 primitive datatypes (stores single values) namely, boolean, byte, char, short, int, long, float, double.Java strictly specifies range and behaviors of all the primitive datatypes. Making the users choose the required datatypes based on the application thus reducing the unused occupancy of memory.For example, if you need to store an integer constant of single digit using integer would be a waste of memory instead, you can use byte type since 8 bits would be necessary to store it.ExampleFollowing Java example lists out the ranges of the primitive datatypes.public class ... Read More

The println() method of the System class accepts aStringas parameter an prints the given String on the console.Examplepublic class PrintData {    public static void main(String args[]) {       System.out.println("Hello how are you");    } }OutputHello how are youIn addition to this you can print data on the console in several other ways, some of them are −Using Output StreamsUsing output stream classes, you can write dat on the specified destination. You can print data on the screen/console by passing the standard output Stream object System.out as source to them.Exampleimport java.io.IOException; import java.io.OutputStreamWriter; public class PrintData {   ... Read More

When you create instance variables in Java you need to initialize them, else the compiler will initialize on your behalf with default values which are −byte: 0short: 0int: 0long: 0float: 0.0double: 0.0boolean: falsestring: nullExampleIn the following Java program prints the default values of the numeric and non-numeric primitive variables in java.public class DefaultValues {    byte byteVariable;    short shortVariable;    int intVariable;    long longVaraible;    float floatVariable;    double doubleVariable;    boolean boolVariable;    String stringVariable;    public static void main(String args[]){       DefaultValues obj = new DefaultValues();       System.out.println("Default values of numeric variables ... Read More

When a class has two or more methods by the same name but different parameters, at the time of calling, based on the parameters passed, respective method is called (or respective method body will be bonded with the calling line dynamically). This mechanism is known as method overloading.Exampleclass Test{    public int addition(int a, int b){       int result = a+b;       return result;    }    public int addition (int a, int b, int c){       int result = a+b+c;       return result;    }    public static void main(String args[]){ ... Read More

A static block is a block of code with a static keyword. In general, these are used to initialize the static members of a class. JVM executes static blocks before the main method at the time loading a class.Examplepublic class MyClass {    static{       System.out.println("Hello this is a static block");    }    public static void main(String args[]){       System.out.println("This is main method");    } }OutputHello this is a static block This is main methodA constructor is similar to method and it is invoked at the time creating an object of the class, it is ... Read More

Whenever you inherit/extend a class, a copy of superclass’s members is created in the subclass object and thus, using the subclass object you can access the members of both classes.ExampleIn the following example we have a class named SuperClass with a method with name demo(). We are extending this class with another class (SubClass).Now, you create an object of the subclass and call the method demo().class SuperClass{    public void demo() {       System.out.println("demo method");    } } public class SubClass extends SuperClass {    public static void main(String args[]) {       SubClass obj = new ... Read More

Inheritance can be defined as the process where one (parent/super) class acquires the members (methods and fields) of another (child/sub).If two classes are related to each other with inheritance. If the super class and sub class contains same methods (same name and arguments), When we invoke this it using the sub class object, the method of the sub class will be executed. This mechanism is known as overriding.Overriding final methodsOnce you declare a method final it cannot be overridden If you try to do so, it generates a compile time error −Exampleclass Super{    public final void demo() {     ... Read More

A method which does not have body is known as abstract method. It contains only method signature with a semi colon and, an abstract keyword before it.public abstract myMethod();To use an abstract method, you need to inherit it by extending its class and provide implementation (body) to it. If a class contains at least one abstract method, you must declare it abstract.In other words, if you extend an abstract class it is mandatory to implement (override) all the abstract methods in it or, declare it abstract else a compile time error will be generated for each abstract method (that you ... Read More

Yes, the super class reference variable can hold the sub class object actually, it is widening in case of objects (Conversion of lower datatype to a higher datatype).But, using this reference you can access the members of super class only, if you try to access the sub class members a compile time error will be generated.ExampleIn the following Java example, we have two classes namely Person and Student. The Person class has two instance variables name and age and one instance method displayPerson() which displays the name and age.The Student extends the person class and in addition to the inherited ... Read More

When write a Java program/class first of all you need to compile it using the javac command as −javac [name of the class].javaIf your program gets compiled without errors, a .class file (byte code) is created with the specified name. Then you need to execute it using the java command (JVM) as −java [class name]ExampleSuppose we Have created a simple class Calculator which adds two or, three numbers in the file with name Calculator.java in the path D:\sample as −public class Calculator {    int addition(int a , int b){       int result = a+b;       ... Read More