A set is an interface in java which is used to maintain the list of an object is a sequence
The main difference between List and Set interface is set interface
always contains unique value no any duplicate value in set interface.
This Set
Interface is implemented by HashSet class and LinkedHashSet Class and extended
by SortedSet interface. The set interface doesn’t have own method for
implementation but it uses the its parent Collection interface method and
provide some restriction so that it doesn’t contain any duplicate value. Order
in the Set interface is implementation dependent. Set contain only one null
element.
HasSet
Class
The
HashSet Class is the implementation of Set interface. This class will contain
only unique values. It allows only one null element. Internally HashSet use
HashMap to stores the objects. the element will we store in the HashSet object
it will be stored as a HashMap means it will contain the key and value. The key
itself is a HashMap and it value is constant which is also called present.
Note: in above example I trying to insert the duplicate value but it
doesn’t insert and also it just includes one null value. It doesn’t have any
order to insert the elements.
LinkedHashSet Class
LinkedHashSet
Class is implement the Set Interface. But this class will insert the element in
ordered base. This class is extending the HashSet Class. Internally this class useLinkedHashMap
class to sotre the elements in an object.
Example
SortedSet
Interface
The
sortedSet Interface is implements the Set interface. This interface is used to
sort the elements in ascending order. It provides the several methods to get
the advantage of sorting. This interface cannot have null element and also
cannot have duplicate element. This interface also sorts the element according
to given comparator. This interface is extending by the NavigableSet
Interface than that NavigableSet interface is implements by TreeSet
Class. interface in java used list object
TreeSet
Class
The
TreeSet class is implement the NavigableSet interface and this interface
extends the SortedSet Interface. This class will sort the element according to
natural ascending order or according to given comparator.
Example
Map
interface is the interface of Java Collections Framework. Like List, Set and
Queue interface it cannot inherit the Collection interface. Map Interface
itself maintain the hierarchy like Collection Interface. This Map interface
stores each value as a key in an object. Every single value has a unique Key.
HashMap class and LinkedHashMap Class implement the Map Interface and SortedMap
extend the Map Interface.
o
Map
interface is a part of Java Collection Framework, but it doesn’t inherit Collection Interface.
o
Map
interface stores the data as a key-value pairs where
each key is associated with a value.
o
A
map cannot have duplicate keys but can
have duplicate values.
o Each
key at most must
be associated with one value.
o
Each
key-value pairs of the map are stored as Map.Entry objects. Map.Entry is an inner
interface of Map interface.
o
The
common implementations of Map interface are HashMap, LinkedHashMap and TreeMap.
o
Order
of elements in map is implementation dependent. HashMap doesn’t maintain any order of elements.LinkedHashMap maintains insertion order of elements. Whereas TreeMap places the elements according to
supplied Comparator.
o
The
Map interface provides three methods, which allows map’s contents to be viewed
as a set of keys(keySet() method), collection of values (values()
method), or set of key-value mappings (entrySet()
method).
HashMapClass
The
HashMap class implement the Map interface. This class store unique elements
with key and pair. The key is always unique. The class contain one null key and
multiple null values and this class has no order of maintenance.
Example
LinkedHashMap
Class
The LinkedHashMap
class implement the Map interface. This class store unique elements with key
and pair. The key is always unique. The class contain one null key and multiple
null values and this class has order of maintenance.
Example:
SortedMap
Interface
The
sortedMap Interface is implements the Map interface. This interface is used to
sort the elements in ascending order. It provides the several methods to get
the advantage of sorting. This interface cannot have null element and also
cannot have duplicate element. The elements will store as a Key and Value
base.
TreeMap
Class
The TreeMap
class is implement the NavigableMap interface and this interface extends the
SortedMap Interface. This class store unique elements with key and pair. The
key is always unique. The class contain one null key and multiple null values
and this class maintain the order according to the natural ascending order.
Example
Note:
In
collection framework, the collections class provide the static method for
sorting the element of collection but that static method will only work with
Set Interface implement class TreeSet and we cannot sort the element of List
interface. So, in order to possess the sorting of List interface,we will use
Collections Class method for sort the List. In order to maintain the order of
any Collection interface than the java provide us two types of interfaces.
o
Collections
Class
o
Comparable
Interface
o
Comparator
Interface
Collections Class
As in
above we discuss some collection framework. Now Collection framework provide
some built-in algorithms which are commonly used in Java. These algorithms are
implements by Collections Class. Collections class implement lot of methods but
we are going to provide you some common and useful methods with implementation.
Example
Comparable
Interface
This
interface is used to maintain the order of user defined class. This interface
contains one method which is “compareTo (Object object)”. This method
compares the current object value with specified object value. This interface
sort the sequence of Any Collections class with single data member.
Example
In this
example we created two classes
EmployeeDetail.java
employee.java
Comparator Interface
This interface is used to maintain the order of user defined class. This
interface contains two methodsin which one is “compare (Object object1,
Object object2)” and second is “equals (Object object)”. The compare
method compares the both objects value each other. This interface sort the
sequence of Any Collections class with multiple data member.
Generics.............
Java
provide one of the power mechanism knowns as Generics. Generics provides the
concept of objects safe type. Which means the generics force the programmers to
specify the suitable Object type. By using generics then we no need of Type
Casting. interface in java used list object
Syntax
ClassOrInterface<type>
As you
notice in above program we created two arrayList one is without generic and
second is with generic type so it is possible to get error at run time during
execution of collection with generic because we don’t know the type of object. interface in java used list object
Generic Class
In this
section we will learn that how to create own generic class.
Syntax
class ClassName<T1, T2, T3,
…. ,Tn>{
}
T1, T2,
T3, ….. , Tn here T stand for Type.
Example with Generic Class
Now in above we create a simple Generic Class Type parameter. This class
contain one Type data member, one constructor and the setter and getter method
that Type data member. As we create the instance of above class then we specify
the Type parameter, once you specify the Type parameter then it will support
only that type of data otherwise it will throw exception. For example, if you
create the Instance of above class with String type than it will only support
String value.
interface in java used list object
Generic
work with only Derived type if you put any primitive type in parameter type it
will give you compile time error.
Example with Two Type Parameter
When you
want only some part of any class or interface to be a generic rather than the
whole class or interface to be a generic than generic methods or constructors
are the best solution of this type of thing.
You can
create both method and constructor in non-generic class, there is no any
restriction of that. You can also create static and non-static methods.
Example
interface in java used list object
Now in
above as we notice that you do not need to use Drive class forcefully, you can
also use primitive data type Instead of Derives datatypes.
Generic
Naming Convention
As you
notice that in above I always using T for generic. Actually it is not necessary
that for generic you can always write T. You just have to provide a Generic
with any Letter but letter should be a Capital here in above we specify T which
means Type so its easily for reading that’s why I specify it.
For
example, if you want to create Map <Key, Value> so its generic will be
look like this Map <K, V>. now this is what say K means Key and V Means
Value.
Generic
Interface
Like
generic class you can create generic interface.
Syntax
Interface
interfaceName<type> {
// implements
method declaration
}
Rules
o
To
implement the generic interface,you must have generic class.
o
Normal
class does not implement the generic interface. if you trying to implement the
generic interface non-generic class you will get compile time error.
o
Normal
class can implement the interface if and only if the generic interface has
wrapper class like: Integer, Double, Float, Long etc.
o
The
generic class that implement the generic interface that at least must has same
type of parameter and same number of parameter.For example: your generic
interface is “interface myInterfce<T1, T2, T3>” then implement
class must have same number of parameter and also same type of parameter “class
myClass<T1, T2, T3> implements myInterface<T1, T2, T3>” or “class
myClass<T1, T2, T3, T4> implements myInterface<T1, T2, T3>”.
But if you write this “class myClass<T1, T3, T5> implements
myInterface<T1, T2, T3>” then, you will get an error because the
number of parameter are same but type of parameter is different.
Java Date
In java
following classes are able to represent the date and time in java.
o
Java.util.Date
class
o
Java.sql.Date
class
o
Java
.text class
Java.util.Date
class
In java
the java.util.Date class used to represent the date and time. It provides some
constructor and methods
Constructor
No.
|
Constructor
|
Description
|
1)
|
Date(long milliseconds)
|
Creates a sql date object
for the given milliseconds since January 1, 1970, 00:00:00 GMT.
|
Methods
No.
|
Method
|
Description
|
1)
|
void setTime(long time)
|
changes the current sql
date to given time.
|
2)
|
Instant toInstant()
|
converts current sql date into Instant object.
|
3)
|
LocalDatetoLocalDate()
|
converts current sql date
into LocalDate object.
|
4)
|
String toString()
|
converts this sql date object to a string.
|
5)
|
static Date
valueOf(LocalDate date)
|
returns sql date object
for the given LocalDate.
|
6)
|
static Date valueOf(String date)
|
returns sql date object for the given String.
|
Java.text
class
In Java
the java.text is a package which contains lot of class and interface and this
package provides the two different classes for date and time. Which are the
following
o
DateFormat
class
o
SimpleDateFormat
class
DateFormat
Class
This
class provide the different type of method to format the date and time
DateFormat
Fields
o
protected Calendar calendar
o
protected NumberFormat numberFormat
o
public static final int ERA_FIELD
o
public static final int YEAR_FIELD
o
public static final int MONTH_FIELD
o
public static final int DATE_FIELD
o
public static final int HOUR_OF_DAY1_FIELD
o
public static final int HOUR_OF_DAY0_FIELD
o
public static final int MINUTE_FIELD
o
public static final int SECOND_FIELD
o
public static final int MILLISECOND_FIELD
o
public static final int DAY_OF_WEEK_FIELD
o
public static final int DAY_OF_YEAR_FIELD
o
public static final int DAY_OF_WEEK_IN_MONTH_FIELD
o
public static final int WEEK_OF_YEAR_FIELD
o
public static final int WEEK_OF_MONTH_FIELD
o
public static final int AM_PM_FIELD
o
public static final int HOUR1_FIELD
o
public static final int HOUR0_FIELD
o
public static final int TIMEZONE_FIELD
o
public static final int FULL
o
public static final int LONG
o
public static final int MEDIUM
o
public static final int SHORT
o
public static final int DEFAULT
Methods
No.
|
Public Method
|
Description
|
1)
|
final String format(Date
date)
|
converts given Date
object into string.
|
2)
|
Date parse(String source)throws ParseException
|
converts string into Date object.
|
3)
|
static final
DateFormatgetTimeInstance()
|
returns time formatter
with default formatting style for the default locale.
|
4)
|
Static final DateFormatgetTimeInstance(int style)
|
returns time formatter with the given formatting style for the
default locale.
|
5)
|
static final
DateFormatgetTimeInstance(int style, Locale locale)
|
returns time formatter
with the given formatting style for the given locale.
|
6)
|
static final DateFormatgetDateInstance()
|
returns date formatter with default formatting style for the
default locale.
|
7)
|
static final
DateFormatgetDateInstance(int style)
|
returns date formatter
with the given formatting style for the default locale.
|
8)
|
static final DateFormatgetDateInstance(int style, Locale locale)
|
returns date formatter with the given formatting style for the
given locale.
|
9)
|
static final
DateFormatgetDateTimeInstance()
|
returns date/time
formatter with default formatting style for the default locale.
|
10)
|
static final DateFormatgetDateTimeInstance(intdateStyle,inttimeStyle)
|
returns date/time formatter with the given date formatting style
and time formatting style for the default locale.
|
11)
|
static final
DateFormatgetDateTimeInstance(intdateStyle, inttimeStyle, Locale locale)
|
returns date/time
formatter with the given date formatting style and time formatting style for
the given locale.
|
12)
|
static final DateFormatgetInstance()
|
returns date/time formatter with short formatting style for date
and time.
|
13)
|
static Locale[]
getAvailableLocales()
|
returns an array of
available locales.
|
14)
|
Calendar getCalendar()
|
returns an instance of Calendar for this DateFormat instance.
|
15)
|
NumberFormatgetNumberFormat()
|
returns an instance of
NumberFormat for this DateFormat instance.
|
16)
|
TimeZonegetTimeZone()
|
returns an instance of TimeZone for this DateFormat instance.
|
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