Techno Mindz

Android operating system is stack of software components which is divided in four layers and five sections.

Linux kernel : 
Linux kernel provides a level of abstraction between the device hardware and it contains all the essential hardware drivers like camera, keypad, display etc. Also, the kernel handles all the things that Linux is really good at such as networking and a vast array of device drivers.

Libraries : 
On top of Linux kernel there is a set of libraries including open-source Web browser engine WebKit, well known library libc, SQLite database which is a useful repository for storage and sharing of application data, libraries to play and record audio and video, SSL libraries responsible for Internet security etc.

Android Libraries : 
This category encompasses Java-based libraries that are specific to Android development. Libraries in this category include the application framework libraries in addition to those that facilitate user interface building, graphics drawing and database access.

• android.app − Provides access to the application model.
• android.content − Facilitates content access, publishing and messaging between applications and application components. 
• android.database − Used to access data published by content providers and includes SQLite database management classes.
• android.opengl − A Java interface to the OpenGL ES 3D graphics rendering API.
• android.os − Provides applications with access to standard operating system services including messages, system services and inter-process communication.
• android.text − Used to render and manipulate text on a device display.
• android.view − The fundamental building blocks of application user interfaces.
• android.widget − A rich collection of pre-built user interface components such as buttons, labels, list views, layout managers, radio buttons etc.
• android.webkit − A set of classes intended to allow web-browsing capabilities to be built into applications.

instanceof operator is also known as type comparison operator. It compares an object with any specific type(may be class, interface etc.). It returns either true or false.
It is used to test whether given object is an instance of specified class or not.

Example :

class Test{
public static void main(String args[]){
Test t=new Test();
System.out.println(t instanceof Test ) ;

}

Output :
true

In the last post we learned some basic operators. Apart from these operators, there are some other operators we need to know about.

In this post post, we will learn Ternary operator.


Ternary operator(?:) : 
                                   This operator is also called conditional operator. It   contains three operands and is used to evaluate boolean expressions. Goal of this operator is to decide which value should be assigned to variable.
Syntax :
 Variable v=(expression) ? value if true : value if false ;                                                                               
Example : 



Output : 

Value of y : 15
Value of y : 10

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Java operators                                                                 instanceof operator

Unicode system  is universal international standard character encoding which is capable to represent most of the world's languages.

Before Unicode system there were several encoding systems

1 . ASCII - Supports language of united states.
2 . ISO 8859-1 - It supports western European language.
3 . KOI-8 - Supports Russian language.
4 . GB18030 and BIG-5 - Supports Chinese language.

This caused the following problem.

A particular code value corresponds to different letters in the various language standards and The encodings for languages with large character sets have variable length.Some common characters are encoded as single bytes, other require two or more byte.

                 To solve this problem, A new encoding system was developed called Unicode system which supports world's most of the languages. In unicode, character holds 2 bytes, so java also uses 2 bytes for characters.

Lowest value in unicode system- \u0000
Highest value in unicode system- \uFFFF

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Jdk, jre, jvm                                                                                                     Java operators

@Override
 public void onCreate(SQLiteDatabase sqLiteDatabase) {
            sqLiteDatabase.execSQL("create table\t"+TABLE_NAME+"\n"+"("+
            COLUMN_ONE+"\t integer primary key ,\n"+
            COLUMN_TWO+"\t"+"varchar(50),\n"+
            COLUMN_THREE+"\t"+"varchar(20));");
 }

  public void insertRecord(Customer customer){
    SQLiteDatabase db=getWritableDatabase();
    ContentValues cv=new ContentValues();
    cv.put(COLUMN_ONE,customer.getCustomerId());
    cv.put(COLUMN_TWO,customer.getCustomerName());
    cv.put(COLUMN_THREE,customer.getCustomerNumber());
    db.insert(TABLE_NAME,null,cv);
 }

public boolean delete(String customerId){

    boolean status=false;
    SQLiteDatabase db=getWritableDatabase();
    if(db!=null){

        status=db.delete(TABLE_NAME,COLUMN_ONE+"\t="+customerId,null)>0;
    }
    return status;
}

   public boolean update(String customerId,String customerName,String customerNumber){
    boolean status=false;
    String updateQuery="Update table\t"+TABLE_NAME+"\t set\t"+COLUMN_TWO+"\t="+customerName+"\t,"+
                        COLUMN_THREE+"\t="+customerNumber+"\t where\t"+COLUMN_ONE+"="+customerId;
    SQLiteDatabase db=getWritableDatabase();
    if(db!=null){
        ContentValues cv=new ContentValues();
        cv.put(COLUMN_TWO,customerName);
        cv.put(COLUMN_THREE,customerNumber);
       status=db.update(TABLE_NAME,cv,COLUMN_ONE+"\t="+customerId,null)>0 ;
    }
    return status;
}

                                                                                                               
JVM- jvm(java virtual machine) is a specification which does the following
         works.

1 . Loads code.
2 . Verifies code.
3 . Executes code.
4 . Provides Runtime environment in which byte code gets executed.



JVM internal architecture






JRE - jre acronym for java runtime environment  is an implementation of
         JVM. It contains set of libraries and other files that JVM uses at runtime.
         We can say JVM is a part of JRE.

     



JDK - JDK is the java development kit which contains development tools and
         JRE.




JVM, JRE and JDK all are platform dependent.

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                                                                                             Unicode system