Java Abstraction

Abstract class is a class that is declared abstract
*  it may or may not include abstract methods.
*  Abstract classes cannot be instantiated, but they can be subclassed.
*  If a class includes abstract methods, the class itself must be declared abstract.
* When an abstract class is subclassed, the subclass must have implementations for all of the 
   abstract  methods.
* When an abstract class inherited from an abstract class there is no need to 
  implement its super abstract methods

Abstract method is a method that is declared without an implementation:(without braces, and followed by a semicolon)
abstract void setUserName(String name);

Java Overloading

Overloading is the same method name with different parameters.
the Constructors can be overloaded
**Methods with Same name in The Class or its Subclasses with different Signature.

Signature (Parameters DataTypes or Number)ex
Class A{
public A(){....}
public A(int x){....}
public A(char x){....}
public void getSomeThing(){.....}
public void getSomeThing(char x){.....}
public void getSomeThing(String x,int y){.....}
public void getSomeThing(double x){.....}
}
Class B extends A{
public void getSomeThing(String x,char y){.....}
}
** You can pass float or double to method who's parameter datatype is double but contrary is prohibited


The overloaded methods can be static , final and or abstract.


Hint: Java uses method Parameters Types and count to specify which method.
Java doesn't differentiate between methods depending on there return DataType 


Hint: Use Overloading when you need multiple methods with different parameters, but methods do the same thing.
Don't use Overloading when methods do different tasks


For more info: http://www.java-samples.com/showtutorial.php?tutorialid=284

Null returned when using findViewById

Hello,
sometime you have nullpointerexception when using findViewById like the code snippet bellow
                TextView tv=(TextView)findViewById(R.id.textViewVV);
if(tv!=null)
tv.setText("Not Null");
this is done because you call different of the set layout
the solution is to call views from the layout you use on the current Activity
like this

setContentView(R.layout.test);

TextView tv=(TextView)findViewById(R.id.textViewVV);

if(tv!=null)

tv.setText("Good");

textViewVV is in test layout, so, this code works fine.

Read file into byte array in j2me

import java.io.InputStream; import java.io.OutputStream; import javax.microedition.io.Connector; import javax.microedition.io.file.FileConnection; /**
 * This class to read file from memory and create a file on phone memory
 * @author Mohammad Abu Hmead
 * 08.03.11
 */
public class CreateAndReadFileOnAndFromMemory {

    public static final String FILE_LOCATIO_IN_PHOTOS=System.getProperty("fileconn.dir.photos");
    public static final String FILE_LOCATIO_IN_VIDEOS=System.getProperty("fileconn.dir.videos");
    public static final String FILE_LOCATIO_IN_TONES=System.getProperty("fileconn.dir.tones");
    public static final String FILE_LOCATIO_ON_MEMORY_CARD=System.getProperty("fileconn.dir.memorycard");
    
    private String fileLocationURL="Not specified yet";

    public CreateAndReadFileOnAndFromMemory(String fileLocation,String fileNameWithItsExtension)
    {
        fileLocationURL=fileLocation+fileNameWithItsExtension;
    }
    public String getFileLocationURL(){
        return fileLocationURL;
    }
    public void setFileLocationURL(String fileLocationURL) {
        this.fileLocationURL = fileLocationURL;
    }

    public void writeIntoFile(String textToBeWritten) throws Exception
    {
            FileConnection fileConnection;

            fileConnection = (FileConnection) Connector.open(fileLocationURL, Connector.READ_WRITE);

            if(!fileConnection.exists())
                fileConnection.create();

            OutputStream outputStream=fileConnection.openOutputStream();
            outputStream.write(textToBeWritten.getBytes("UTF-8"));
            
            outputStream.flush();
            outputStream.close();
            fileConnection.close();
    }

    public boolean  createFileOnMem(byte[]  fileBs) throws Exception
    {
        boolean isCreated=false;
        try {
            FileConnection fileConnection;
            fileConnection = (FileConnection) Connector.open(fileLocationURL, Connector.READ_WRITE);
            if(!fileConnection.exists())
                fileConnection.create();

            OutputStream outputStream=fileConnection.openOutputStream();
            outputStream.write(fileBs);
            outputStream.flush();
            outputStream.close();
            fileConnection.close();
            isCreated=true;
        } catch (Exception e) {
        }
            

        return isCreated;
            
    }

    public byte[] readFileByts() throws Exception
    {
        byte[] filebBs=null;

        FileConnection fileConnection = (FileConnection)
                Connector.open(fileLocationURL, Connector.READ_WRITE);
        if(fileConnection.exists())
        {
            filebBs=new byte[(int)fileConnection.fileSize()];
            InputStream is=fileConnection.openInputStream();
            is.read(filebBs, 0, filebBs.length);
            is.close();
            is=null;
            fileConnection.close();
        }
        return filebBs;
    }

    public boolean deleteTheFile()
    {
        boolean isDeleted=false;
        FileConnection fileConnection;
        try {
            fileConnection = (FileConnection) Connector.open(fileLocationURL, Connector.READ_WRITE);
            if(fileConnection.exists())
            {
                fileConnection.delete();
                isDeleted=true;
            }
        } catch (Exception ex) {

        }
        return isDeleted;
    }
}