The abstract keyword is used to declare methods abstract methods and abstract classes. Once a method is declared abstract we should not specify body for those. And once a class is declared abstract it cannot be instantiated. Example Live Demo abstract class Employee { private String name; private String address; private int number; public Employee(String name, String address, int number) { System.out.println("Constructing an Employee"); this.name = name; ... Read More

You can pass final variables as the parameters to methods in Java. A final variable can be explicitly initialized only once. A reference variable declared final can never be reassigned to refer to a different object. However, the data within the object can be changed. So, the state of the object can be changed but not the reference. With variables, the final modifier often is used with static to make the constant a class variable. Example Live Demo public class Test{ public void sample(final int data){ System.out.println(data); ... Read More

The scope of the private modifier lies with in the class. Members that are declared private cannot be accessed outside the class. Private access modifier is the most restrictive access level. Class and interfaces cannot be private. Variables that are declared private can be accessed outside the class, if public getter methods are present in the class. Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world. Example The following class uses private access control public class Logger { private String format; ... Read More

A final variable can be explicitly initialized only once. A reference variable declared final can never be reassigned to refer to a different object. However, the data within the object can be changed. So, the state of the object can be changed but not the reference. With variables, the final modifier often is used with static to make the constant a class variable. Therefore, once we declare a final variable it is mandatory to initialize the final variable at the time of declaration or using constructor. If not, a compile time error may occur saying “The blank final field num ... Read More

Default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc. The scope of the default access modifier lies within the package. When a class or its members associated with default access modifier then. Example Variables and methods can be declared without any modifiers, as in the following examples: String version = "1.5.1"; boolean processOrder() { return true; }

When a variable, method or constructor that are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class. The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected. Protected access gives the subclass a chance to use the helper method or variable, while preventing a nonrelated class from trying to use it. Example The following parent class uses protected access control, to allow its child class ... Read More

Class variables also known as static variables are declared with the static keyword There would only be one copy of each class variable per class, regardless of how many objects are created from it. You can access a class variable without instantiation using the class name as className.variableName. Example Live Demo public class Test{ static int num = 92; public static void main(String args[]) throws Exception { System.out.println(Test.num); } } Output 92

The public modifier has the widest scope. When a class or its members declared public they are accessible from everywhere. A default class or its members are available to any other class in the same package. However, if the public class we are trying to access is in a different package, then the public class still needs to be imported. Because of class inheritance, all public methods and variables of a class are inherited by its subclasses. Example The following function uses public access control − public static void main(String[] arguments) { // ... } ... Read More

Local variables are declared in methods, constructors, or blocks. Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block. A local variable is the one which is declared within a method. The scope of this variable is within the method. Example public abstract class Sample { public static void main(String args[]){ int data = 4044; System.out.println(data); } } Output 4044

When we haven’t initialized the instance variables compiler initializes them with default values.For boolean type, the default value is false, for float and double types default values are 0.0 and for remaining primitive types default value is 0.ExampleLive Demopublic class Sample {    int varInt;    float varFloat;    boolean varBool;    long varLong;    byte varByte;    short varShort;    double varDouble;    public static void main(String args[]){       Sample obj = new Sample();       System.out.println("Default int value ::"+obj.varInt);       System.out.println("Default float value ::"+obj.varFloat);       System.out.println("Default boolean value ::"+obj.varBool);     ... Read More