Containers in java
Container is java feature, it includes other java
programming elements like variables, method, constructor ………………
There are three types of container in java
1.
class
2.
Abstract class
3.
Interface
Date: july-14-2016
1.
class
class is a java feature. It able to represent all the real world entities
like Student, Employee, Customer, Product, Account ……..
Syntax:-
[Access_modifiers] class class_Name[extends Super_Class_Name][implements
Interface_List]
{
--Variables--
--Methods--
--Constructors--
--blocks--
--classes--
--abstract classes--
--interfaces--
--enums--
}
There are two types of Access Modifiers in java
1. To define scopes
to the programming elements like variables, methods, classes,
We have to use the following list of Access Modifiers
1.
public
2.
protected
3.
<Default>
4.
private
where “private” members are available up to the respective
class where the members are declared.
Where “<default>” member are available up to the
current packages not available to outside of the current packages.
Where “protected” member are available up to the present
package and up to the child classes available in other packages
Where “public” member are available throughout the
application or throughout the system.
From the above access modifiers, only public and
<default> access modifiers are allowed in class syntax, but inner classes
are able to allow all the above access modifiers.
Note :-
The access modifiers
like private and protected are defined on the bounded of the classes, so that,
these access modifiers is not applicable for classes, but, these access
modifiers an applicable for members and the classes including inner classes.
2.
To defined some extra nature to the programming
elements like variables, methods, classes ,… we have to use the following list
of access modifiers.
static
final
abstract
native
volatile
transient
synchronized
strictfp
----
----
From the above list of access modifiers only final, abstract
and scriptfp access modifiers are allowed in class syntax, but inner classes
are able to allow the access modifiers like static, final, abstract, strictfp
Note:-
In java application, “static” keyword is defined is on the
boundaries of the classes, so that, it can not be used for classes, we can use
static keyword for members of the classes including inner classes.
Where “class” is a java keyword, it can be used to represent
“class” object oriented features and it can be used to declare classes in java
application.
Where “Class_Name” is on identifiers to recognized the
classes independently.
Where “extends” is a java keyword, it can be used to provide
a super class name in the class syntax in order to reuse variable and methods
of the specified super class in the present java class .
Date: july-15-2016
Note 1:-
In class syntax, “extend” keyword is able to allow only are
super class name, it will not allow more then one super class name. if we
provide more then our super class name along with extends keyword then it will
represented multiple inheritance, it is not possible in java.
Where “implements” is a java keyword, it can be used to specify
one or more number of interface names to implements interface methods in the
present java class.
Note 2:-
In class syntax, “implements” keyword is able to allow more
then one interface name.
Note 3:-
In class syntax, both extends and implements keywords are
optional, we can write a class with out
extends keyword and with implemented keyword, we can write a class with out
implemented keyword and with extended keyword, we can write a class with out to
provide both extends and implement keywords. First we have to provide extends
keyword then we have to provide implements keywords.
1. public class A{ }--->Valid
2. public class A{ }--->Invalid
3. class A{ }--->Valid
4. private class A{ }--->Invalid
5. class A{private class B{}}-->Valid
6. class A{public class B{}}---->Valid
7. class A{protected class B{}}-->Valid
8. static class A{}--->Invalid
9. final class A{}---->Valid
10. abstract class A{}--->Valid
11. strictfp class A{}-->Valid
12. class A{static class B{}}--->Valid
13. class A{transient class B{}}-->Invalid
14. class A extends B{}-->Valid
15. class A extends B,C{}--->Invalid
16. class A extends B extends C{}-->Invalid
17. class A implement I{}-->Valid
18. class A implement I1,I2{}-->Valid
19. class A implement I extends B{}-->Invalid
20. class A extends B implement I{}-->Valid
Process to use classes in java application
a.
Declare a class by using “class” keyword.
b.
Declare variable and method as per the
application requirements in user defined class.
c.
In main class, in main() method, create
object for the respective class.
d.
Access the members of the respective class by
using the generated reference variable.
Ex
code:-
class Employee
{
String
eid="E-111";
String
ename="Sai";
float
esal=50000.0f;
String
eadd="Hyderabad";
String
eemail="jntusuperfastupdates@gmail.com";
String
emobile="91-9553667049";
public
void getEmployeeDetails()
{
System.out.println("Employee
details");
System.out.println("___________________");
System.out.println("Employee
Id :"+eid);
System.out.println("Employee
Name :"+ename);
System.out.println("Employee
Salary :"+esal);
System.out.println("Employee
Address :"+eadd);
System.out.println("Employee
Email :"+eemail);
System.out.println("Employee
Mobile :"+emobile);
}
}
class Test
{
public
static void main(String[] args)
{
Employee
emp=new Employee();
emp.getEmployeeDetails();
}
}
Output:-
Employee details
___________________
Employee Id :E-111
Employee Name :Sai
Employee Salary :50000.0
Employee Address :Hyderabad
Employee Email :jntusuperfastupdates@gmail.com
Employee Mobile :91-9553667049
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