Basic definitions in Java

CLASS

1.collection of obects is called as classs and it is logical entity

2.class is a group of object which have common properties

OBJECT

1.it is defined as an instance of a class

2.an entity that has state and behavior calles as object

JDK==Java Development Kit

JRE==Java Runtime Environment

JVM==Java Virtual Machine

API==Application programming interface-->predefined function that are ready to use

BUILDIND BLOCKS OF JAVA:

1.object

2.variables

3.methods

4.blocks

Variables are 2 types

1.static, 2.Non-static

TYPE CASTING

conversion of data from one type to another type

2 types of casting

inplicit(widening) and explicit(narrow)

implicit== smaller type to larger type

explicit== larger to smaller

Wrapper classes 

convert primitive to object type

Java methods

method is block of code or collection of statement

types of method

1.predefined

2.userdefined

Java Constructors

constructor is a member method which has the same name as class name and never return anything

2types of constructor

 1. default 2.parameterized

Constructor Overloading

it is having more than one constructor with different parameter

Static keyword

it is used for constant variable or method that is same for every instance of class

This keyword

this is a reference variable that refers to the object. 

Packages

it is group of similar type of classes,interface and sub-packages. it is used to group related classes.

2 types of package

1.user defined package

2.built in packages -->eg: java.utill.array

Access Modifiers

it specifies the accessibility of method, constructors, class.

access modifiers are 1.private 2.package 3.protected 4.public 

1.private== within a class

2.package/default == within a package

3.protected== outside the package using extend keyword

4.public == outside the package

OOPs(object oriented principles)

1.Inheritance

Process of defining new object with the help of old objects. extend keywors is used

types

1.single,2.multilevel,3.hierarchial,4.multiple,5.hybrid

Method Overloading

if a class has multiple methods with same name but in different parameter

Method Overriding

child classs having same methos as parent class

Super Keyword

it is reference variable used to refer the immediate parent class object

Final Keyword

cannot be change the values

2.Polymorphism

object of a class behave differently while communicating  with diffrent objects. overloading is used

2 types= compiletime,runtime

3.Abstraction

hiding the internal detail of a object 

interface will achive complete abstraction

Interface

it is bluebrint of a class and it is static constants and abstacts method and cannot have a body

4.Encapsulation

procees of data together in a single unit. using getters and setters

COLLECTION 

The Collection in Java is a framework that provides an architecture to store and manipulate the group of objects.

ArrayList

The ArrayList class implements the List interface. It uses a dynamic array to store the duplicate element of different data types.

Creating arraylist

ArrayList<String> list = new ArrayList<String>();  

LinkedList

it uses a doubly linked list internally to store the elements. It can store the duplicate elements.

HashMap

Java HashMap is a hash table based implementation of Map interface.faster

HashSet

HashSet is a Set. It creates a collection that uses a hash table for storage.slow

Hash Code

The hashCode method is an inbuilt method that returns the integer hashed value of the input value

File Handling in Java

File handling in Java implies reading from and writing data to a file. The File class from the java.io package, allows us to work with different formats of files.

Java Annotations

Java Annotation is a tag that represents the metadata i.e. attached with class, interface, methods or fields to indicate some additional information which can be used by java compiler and JVM.

Annotations in Java are used to provide additional information, so it is an alternative option for XML and Java marker interfaces.

Built-In Java Annotations used in Java code

@Override

@SuppressWarnings

@Deprecated

Garbage Collection

Garbage Collection is process of reclaiming the runtime unused memory automatically. In other words, it is a way to destroy the unused objects.

Exception Handling

Exception Handling is a mechanism to handle runtime errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc

Java Enums

The Enum in Java is a data type which contains a fixed set of constants.