JVM and OOPS Introduction

 static Keyword :
◦ The static keyword is used in java mainly for memory
management.
 Types Of Static Members :
◦ Java supporting four types of static members
1. static variables
2. static blocks
3. static methods
4. main method

 Non-static Members :
◦ Class level members which don’t have static keyword in their
creation statement are called non-static members.
 Types Of Non-static Members :
◦ Java supporting four types of non-static members
1. Non-static variables
2. Non-static blocks
3. Non-static methods
4. Constructors

 Package:
◦ It is a Java folder used to group related classes , interfaces
and enums.
 Class :
◦ Class is a collection of data members and member functions
 Interface :
◦ Interface is a fully unimplemented class , it is used for
defining set of object operations.
 Abstract Class :
◦ A class that is declared with abstract keyword, is known as
abstract class in java

 DataType :
◦ Data type gives information about size of the memory location
and range of data that can be stored inside that location .
1. Primitive types
2. Referenced types
 Primitive Types:
◦ Primitive Data types is used to store single value at a time.

Size and Default value of Primitive type:
Data Type Name Size [ byte( s ) ] Default Value
byte 1 0
short 2 0
int 4 0
long 8 0
float 4 0.0
double 8 0.0
char 2 ‘u0000'
boolean 1 false

 Types of Loop :
◦Java has very flexible three looping mechanisms.
1. while loop
2. do…while
3. for loop
 Enhanced for Loop :
Syntax :
for (data_type variable: array_name){
---------
---------
}

 Switch-case:
◦ A switch statement allows you to test the value of an
expression and, depending on that value, to jump directly to
some location within the switch statement.
 Syntax: switch (expression) {
case value1:
//statement s
break;
------------------------
case value n:
//statements
default:
//default statement sequence
}

 Using String in Switch-case:
◦ In Java SE 7 and later, you can use a String object in
the switch statement's expression.
 Use of instanceof keyword:
◦ The instanceof operator allows you to determine the type of
an object.
Example:- if(employee instanceof Person){
---------------------
---------------------
}

 Class:
oA class can be defined as a template/blue print that describes
the behaviours/states that object of its type support.
 Syntax to declare a class:
class <class_name>{
data member;
method;
}
 Object:
◦ object is the physical reality of a class.
 Object’s characteristics :
1.State
2.Behaviour
3.Identity

 Relationship with Objects:
◦ Java supports three types of relationship:
1.IS-A.(Inheritance)
2.HAS-A.(Composition)
3.USES-A.(Aggregation)
 OOPs Features:
◦ We have mainly four OOPs Features:
1.Encapsulation
2. Inheritance
3. Abstraction
4. Polymorphism

 Encapsulation:
◦ The process of creating a class by Hiding internal data from
the outside.
 Inheritance:
◦ The process of creating a class to reuse exited class member
using our class name or objects is called inheritance.

 Abstraction :
◦ The process of defining a class by providing necessary
details to class objects operation by hiding or removing its
implementation details called abstraction.
 Polymorphism:
◦ The process of defining a class by with multiple methods
with same name but different implementation is called
polymorphism.
 Types of Polymorphism:
1. Compile-time polymorphism.
2. Run-time polymorphism.

 Behaviors of Polymorphism:
◦ we can developed polymorphism by using
1. Method Overloading.
2. Method Overriding
 Return Type Declaration:
◦ Use the return statement to return the value.
◦ Declare a method's return type in its method declaration.
◦ Declare Within the body of the method.

 Types Of Constructor:
◦ Default constructor (no-argument constructor):
A constructor that have no parameters
Ex-
◦ Parameterized constructor:
A constructor that have parameters

 Constructor Overloading:
◦ A class can have any number of constructors that differ in
parameter lists.
 Constructor Chaining:
◦ Calling one constructor from other.
 this Keyword:
◦ this is a reference variable that refers to the current object.
 super Keyword :
◦ super is a reference variable that is used to refer immediate
parent class object.

 Array:
◦ Array is a collection of similar type of elements that have
continuous memory location.
 Array Declaration:
◦ 1 Dimensional Declaration-
Ex-int[] x;
◦ 2 Dimensional Declaration-
Ex-int[][] x;

 Array Initialization :
◦ Syntax-
Datatype arrayName = new datatype[size];
 Array Assignment :
◦ Syntax-
DataType[] arrayRefVar = {value0, value1, ..., value
k};
 Anonymous Array:
◦ Array without any name.
◦ Syntax-new
datatype[]{10,20,30};

JVM and OOPS Introduction

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JVM and OOPS Introduction