Properties class in Java
The properties object contains key and value pair
both as a string. It is the subclass of Hashtable.
It can be used to get property
value based on the property key. The Properties class provides methods to get
data from properties file and store data into properties file. Moreover, it can
be used to get properties of system.
Advantage of properties
file
Easy Maintenance: If any information is changed from the
properties file, you don't need to recompile the java class. It is mainly used
to contain variable information i.e. to be changed.
Methods of Properties class
The commonly used methods of
Properties class are given below.
|
Method
|
Description
|
|
public
void load(Reader r)
|
loads
data from the Reader object.
|
|
public
void load(InputStream is)
|
loads
data from the InputStream object
|
|
public
String getProperty(String key)
|
returns
value based on the key.
|
|
public
void setProperty(String key,String value)
|
sets
the property in the properties object.
|
|
public
void store(Writer w, String comment)
|
writers
the properties in the writer object.
|
|
public
void store(OutputStream os, String comment)
|
writes
the properties in the OutputStream object.
|
|
storeToXML(OutputStream
os, String comment)
|
writers
the properties in the writer object for generating xml document.
|
|
public
void storeToXML(Writer w, String comment, String encoding)
|
writers
the properties in the writer object for generating xml document with
specified encoding.
|
Example of Properties class to get
information from properties file
To get information from the
properties file, create the properties file first.
db.properties
1. user=system
2. password=oracle
Now, lets create the java class
to read the data from the properties file.
Test.java
1. import java.util.*;
2. import java.io.*;
3. public class Test {
4. public static void main(String[] args)throws Exception{
5. FileReader reader=new FileReader("db.properties");
6.
7. Properties p=new Properties();
8. p.load(reader);
9.
10. System.out.println(p.getProperty("user"));
11. System.out.println(p.getProperty("password"));
12. }
13. }
Output:system
oracle
Now if you change the value of
the properties file, you don't need to compile the java class again. That means
no maintenance problem.
Example of Properties class to get all the
system properties
By System.getProperties()
method we can get all the properties of system. Let's create the class that
gets information from the system properties.
Test.java
1. import java.util.*;
2. import java.io.*;
3. public class Test {
4. public static void main(String[] args)throws Exception{
5.
6. Properties p=System.getProperties();
7. Set set=p.entrySet();
8.
9. Iterator itr=set.iterator();
10. while(itr.hasNext()){
11. Map.Entry entry=(Map.Entry)itr.next();
12. System.out.println(entry.getKey()+" = "+entry.getValue());
13. }
14.
15. }
16. }
Output:
java.runtime.name = Java(TM) SE Runtime Environment
sun.boot.library.path = C:\Program Files\Java\jdk1.7.0_01\jre\bin
java.vm.version = 21.1-b02
java.vm.vendor = Oracle Corporation
java.vendor.url = http://java.oracle.com/
path.separator = ;
java.vm.name = Java HotSpot(TM) Client VM
file.encoding.pkg = sun.io
user.country = US
user.script =
sun.java.launcher = SUN_STANDARD
...........
Example of Properties class to create
properties file
Now lets write the code to
create the properties file.
Test.java
1. import java.util.*;
2. import java.io.*;
3. public class Test {
4. public static void main(String[] args)throws Exception{
5.
6. Properties p=new Properties();
7. p.setProperty("name","Bhupender
Dagar");
8. p.setProperty("email","bsdagar01@gmail.com");
9.
10. p.store(new FileWriter("info.properties"),"My java Examples");
11.
12. }
13. }
Let's see the generated
properties file.
info.properties
1. #My
java Examples
2. #Thu Oct 03 22:35:53 IST 2013
3. email=bsdagar01@gmail.com
4. name=Bhupender
Dagar
Difference between
ArrayList and Vector
ArrayList and Vector both implements List
interface and maintains insertion order.
But there are many differences between ArrayList
and Vector classes that are given below.
|
ArrayList
|
Vector
|
|
1)
ArrayList is not synchronized.
|
Vector
is synchronized.
|
|
2)
ArrayList increments 50%of current array size if number of
element exceeds from its capacity.
|
Vector increments
100% means doubles the array size if total number of element exceeds
than its capacity.
|
|
3)
ArrayList is not a legacyclass, it is introduced in JDK 1.2.
|
Vector
is a legacy class.
|
|
4)
ArrayList is fast because it is non-synchronized.
|
Vector
is slow because it is synchronized i.e. in multithreading
environment, it will hold the other threads in runnable or non-runnable state
until current thread releases the lock of object.
|
|
5)
ArrayList uses Iteratorinterface to traverse the elements.
|
Vector
uses Enumeration interface to traverse the elements. But it
can use Iterator also.
|
Example of Java ArrayList
Let's see a simple example where we are using
ArrayList to store and traverse the elements.
1. import java.util.*;
2. class TestArrayList21{
3. public static void main(String args[]){
4.
5. List<String> al=new ArrayList<String>();//creating arraylist
6. al.add("Sonoo");//adding object in arraylist
7. al.add("Michael");
8. al.add("James");
9. al.add("Andy");
10. //traversing elements using Iterator
11. Iterator itr=al.iterator();
12. while(itr.hasNext()){
13. System.out.println(itr.next());
14. }
15. }
16. }
Output:
Sonoo
Michael
James
Andy
Example of Java Vector
Let's see a simple example of java Vector class
that uses Enumeration interface.
1. import java.util.*;
2. class TestVector1{
3. public static void main(String args[]){
4. Vector<String> v=new Vector<String>();//creating vector
5. v.add("umesh");//method of Collection
6. v.addElement("irfan");//method of Vector
7. v.addElement("kumar");
8. //traversing elements using Enumeration
9. Enumeration e=v.elements();
10. while(e.hasMoreElements()){
11. System.out.println(e.nextElement());
12. }
13. }
14. }
Output:
umesh
irfan
kumar
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