Pass By Value and Pass By Reference in java

Java Constuctor

• The constructor in Java have same name as name of class in which they belong.
• The constructor in java does not have any return type, science never return anything.
• The main use of constructor is to initialize the value of the reference variable to instance variable. 
• Java provide a default constructor which takes no arguments and performs no special actions or initializations,when no explicit constructor are provided.

Type conversion

Type Casting  refers to changing an entity of one datatype into another. This is important for the type conversion in developing any application. If you will store a int value into a byte variable directly, this will be illegal operation. For storing your calculated int value in a byte variable you will have to change the type of resultant data which has to be stored.

Automatic Conversion

In Java type conversions are performed automatically when the type of the expression on the right hand side of an assignment operation can be safely promoted to the type of the variable on the left hand side of the assignment. Thus we can safely assign:

byte -> short -> int -> long -> float -> double

lets take an example,

// 64 bit long integer

long myLongValue;

// 32 bit standard integer 

int myIntValue;

myLongValue = myIntValue;

Java follows two types of casting

• Upcasting
•  Downcasting

Upcasting

Casting a reference with the class hierarchy in a direction from the sub classes towards the root then this type of casting is termed as upcasting. Upcasting does not require a cast operator.

DownCasting

On the other hand, casting a reference with hierarchal class order in a direction from the root class towards the children or subclasses, then it is known as downcasting.

Here we discussing one example,where we converting int value to byte.

int x=10;

byte b =(byte) x;

here first we assign the int x to 10;Then we try to convert int x to byte and try to store in the variable byte b.for that we using byte b =(byte) x;

Explicit Conversion (Casting)

Automatic type casting does work in case of narrowing i.e. when a data type requiring more storage is converted into a data type that requires less storage. E.g. conversion of a long to an int does not perform because the first requires more storage than the second and consequently information may be lost. In such situations an explicit conversion is required. 

Variable declaration

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.

Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables.

In java programing language all variables must first be declared before they can be used.This structure involves starting the variable’s type and name.

int nm=1;

Doing so tells your program that a field named “nm” using to hold numerical data .Where “int” is the variable data type and “nm” is the variable name.where we initializing the integer nm value as 1.

byte:

• Byte data type is a 8-bit signed two's complement integer.
• Minimum value is -128 (-2^7)
• Maximum value is 127 (inclusive)(2^7 -1)
• Default value is 0
• Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an int.
• Example : byte a = 100 , byte b = -50

short:

• Short data type is a 16-bit signed two's complement integer.
• Minimum value is -32,768 (-2^15)
• Maximum value is 32,767(inclusive) (2^15 -1)
• Short data type can also be used to save memory as byte data type. A short is 2 times smaller than an int
• Default value is 0.
• Example : short s= 10000 , short r = -20000

int:

• Int data type is a 32-bit signed two's complement integer.
• Minimum value is - 2,147,483,648.(-2^31)
• Maximum value is 2,147,483,647(inclusive).(2^31 -1)
• Int is generally used as the default data type for integral values unless there is a concern about memory.
• The default value is 0.
• Example : int a = 100000, int b = -200000

long:

• Long data type is a 64-bit signed two's complement integer.
• Minimum value is -9,223,372,036,854,775,808.(-2^63)
• Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
• This type is used when a wider range than int is needed.
• Default value is 0L.
• Example : int a = 100000L, int b = -200000L

float:

• Float data type is a single-precision 32-bit IEEE 754 floating point.
• Float is mainly used to save memory in large arrays of floating point numbers.
• Default value is 0.0f.
• Float data type is never used for precise values such as currency.
• Example : float f1 = 234.5f

double:

• double data type is a double-precision 64-bit IEEE 754 floating point.
• This data type is generally used as the default data type for decimal values. generally the default choice.
• Double data type should never be used for precise values such as currency.
• Default value is 0.0d.
• Example : double d1 = 123.4

boolean:

• boolean data type represents one bit of information.
• There are only two possible values : true and false.
• This data type is used for simple flags that track true/false conditions.
• Default value is false.
• Example : boolean one = true

char:

• char data type is a single 16-bit Unicode character.
• Minimum value is '\u0000' (or 0).
• Maximum value is '\uffff' (or 65,535 inclusive).
• Char data type is used to store any character.
• Example . char letterA ='A'
  
  

AlertDialog box with Three buttons in Android

In this activity we using 3 buttons,which are NeturalButton,PositiveButton,NegativeButton.
Here also discussing the coding to dismiss the Activity,dialog box and how moving to next Activity.


The NeturalButton is using to dismiss the dialog box.



b.setNeutralButton("dismiss dialog", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
dialog.dismiss();
}
});

Here the PositiveButton button is using to move from one Activity to another.



b.setPositiveButton("go to next class", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
Intent i=new Intent(AlertDialogExpActivity.this,ss.class);
startActivity(i);
}
});

Here the NegativeButton is using to finish the activity.


b.setNegativeButton("finish class", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
AlertDialogExpActivity.this.finish();
}
});



package com.ann;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;

public class AlertDialogExpActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    public void onClick(View v){
    Builder b=new AlertDialog.Builder(this);
    b.setTitle("AlertDialog with Three Buttons");
    b.setMessage("This is the messageee...!!!");
    b.setNeutralButton("dismiss dialog", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
dialog.dismiss();
}
});
    b.setPositiveButton("go to next class", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
Intent i=new Intent(AlertDialogExpActivity.this,ss.class);
startActivity(i);
}
});
    b.setNegativeButton("finish class", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
AlertDialogExpActivity.this.finish();
}
});
    AlertDialog d=b.create();
    d.show();
    }
}

XML Parsing

AndroidXMLParsingActivity.java

package com.androidhive.xmlparsing;

import java.util.ArrayList;
import java.util.HashMap;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class AndroidXMLParsingActivity extends ListActivity {

    // All static variables
    static final String URL = "http://api.androidhive.info/pizza/?format=xml";
    // XML node keys
    static final String KEY_ITEM = "item"; // parent node
    static final String KEY_ID = "id";
    static final String KEY_NAME = "name";
    static final String KEY_COST = "cost";
    static final String KEY_DESC = "description";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

        XMLParser parser = new XMLParser();
        String xml = parser.getXmlFromUrl(URL); // getting XML
        Document doc = parser.getDomElement(xml); // getting DOM element

        NodeList nl = doc.getElementsByTagName(KEY_ITEM);
        // looping through all item nodes <item>
        for (int i = 0; i < nl.getLength(); i++) {
            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();
            Element e = (Element) nl.item(i);
            // adding each child node to HashMap key => value
            map.put(KEY_ID, parser.getValue(e, KEY_ID));
            map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
            map.put(KEY_COST, "Rs." + parser.getValue(e, KEY_COST));
            map.put(KEY_DESC, parser.getValue(e, KEY_DESC));

            // adding HashList to ArrayList
            menuItems.add(map);
        }

        // Adding menuItems to ListView
        ListAdapter adapter = new SimpleAdapter(this, menuItems,
                R.layout.list_item,
                new String[] { KEY_NAME, KEY_DESC, KEY_COST }, new int[] {
                        R.id.name, R.id.desciption, R.id.cost });
        setListAdapter(adapter);
        // selecting single ListView item
        ListView lv = getListView();
        lv.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                // getting values from selected ListItem
                String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
                String cost = ((TextView) view.findViewById(R.id.cost)).getText().toString();
                String description = ((TextView) view.findViewById(R.id.desciption)).getText().toString();
               
                // Starting new intent
                Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
                in.putExtra("n", name);
                in.putExtra("c", cost);
                in.putExtra("d", description);
                startActivity(in);

            }
        });
    }
}


SingleMenuItemActivity.java

package com.androidhive.xmlparsing;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class SingleMenuItemActivity  extends Activity {
   
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.single_list_item);
        
        // getting intent data
        Intent in = getIntent();
        
        // Get XML values from previous intent
        String name = in.getStringExtra("n");
        String cost = in.getStringExtra("c");
        String description = in.getStringExtra("d");
        
        // Displaying all values on the screen
        TextView lblName = (TextView) findViewById(R.id.name_label);
        TextView lblCost = (TextView) findViewById(R.id.cost_label);
        TextView lblDesc = (TextView) findViewById(R.id.description_label);
        
        lblName.setText(name);
        lblCost.setText(cost);
        lblDesc.setText(description);
    }
}

XMLParser.java





package com.androidhive.xmlparsing;

import java.io.IOException;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import android.util.Log;

public class XMLParser {

    // constructor
    public XMLParser() {

    }

    /**
     * Getting XML from URL making HTTP request
     * @param url string
     * */
    public String getXmlFromUrl(String url) {
        String xml = null;

        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            xml = EntityUtils.toString(httpEntity);

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        // return XML
        return xml;
    }
   
    /**
     * Getting XML DOM element
     * @param XML string
     * */
    public Document getDomElement(String xml){
        Document doc = null;
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        try {

            DocumentBuilder db = dbf.newDocumentBuilder();

            InputSource is = new InputSource();
                is.setCharacterStream(new StringReader(xml));
                doc = db.parse(is); 

            } catch (ParserConfigurationException e) {
                Log.e("Error: ", e.getMessage());
                return null;
            } catch (SAXException e) {
                Log.e("Error: ", e.getMessage());
                return null;
            } catch (IOException e) {
                Log.e("Error: ", e.getMessage());
                return null;
            }

            return doc;
    }
   
    /** Getting node value
      * @param elem element
      */
     public final String getElementValue( Node elem ) {
     Node child;
  if( elem != null){
         if (elem.hasChildNodes()){
                 for( child = elem.getFirstChild(); child != null; child = child.getNextSibling() ){
                 if( child.getNodeType() == Node.TEXT_NODE  ){
                    //System.out.println(child.getNodeValue());
                         return child.getNodeValue();
                    
                 }
                 }
             }
  }
         
         return "";
     }
     
     /**
      * Getting node value
      * @param Element node
      * @param key string
      * */
     public String getValue(Element item1, String str) {       
            NodeList n = item1.getElementsByTagName(str);
        //    System.out.println(n.item(0));
            return this.getElementValue(n.item(0));
        }
}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
    <!-- Main ListView
         Always give id value as list(@android:id/list)
    -->
    <ListView
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"> 
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <!-- Name Label -->
        <TextView
            android:id="@+id/name"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="#dc6800"
            android:textSize="16sp"
            android:textStyle="bold"
            android:paddingTop="6dip"
            android:paddingBottom="2dip" />
        <!-- Description label -->
        <TextView
            android:id="@+id/desciption"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="#acacac"
            android:paddingBottom="2dip">
        </TextView>
        <!-- Linear layout for cost and price Cost: Rs.100 -->
        <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <!-- Cost Label -->
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#5d5d5d"
            android:gravity="left"
            android:textStyle="bold"
            android:text="Cost: " >
        </TextView>
        <!-- Price Label -->
        <TextView
            android:id="@+id/cost"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#acacac"
            android:textStyle="bold"
            android:gravity="left">
        </TextView>
        </LinearLayout>
    </LinearLayout>

</LinearLayout>

single_list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
  <!-- Name Label -->
  <TextView android:id="@+id/name_label"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textSize="25dip"
            android:textStyle="bold"
            android:paddingTop="10dip"
            android:paddingBottom="10dip"
            android:textColor="#dc6800"/>
  <!-- Description Label -->
  <TextView android:id="@+id/description_label"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="#acacac"/>
  <!-- Price Label -->
  <TextView android:id="@+id/cost_label"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              android:textStyle="bold"/>
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.androidhive.xmlparsing"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".AndroidXMLParsingActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <!-- Single List Item View -->
        <activity
            android:label="Single Menu Item"
            android:name=".SingleMenuItemActivity" >
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />

</manifest>

Alarm with Service and BroadcastReceiver

 AlarmServiceActivity.java


package com.ann;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class AlarmServiceActivity extends Activity {
    EditText txt;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
       
    }
    public void start(View v){
        txt=(EditText)findViewById(R.id.txt);
        int i=Integer.parseInt(txt.getText().toString());
        Intent intent=new Intent(this,myBroadcast.class);
        PendingIntent intt=PendingIntent.getBroadcast(this, 234, intent, 0);
       
        AlarmManager alarm=(AlarmManager)getSystemService(ALARM_SERVICE);
       alarm.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()+(i*1000), intt);
       //startService(new Intent(this,Myservice.class));

       Toast.makeText(this, "Alarm set in " + i + " seconds",
                Toast.LENGTH_LONG).show();
       
    }
   public void stop(View v){
      Intent i=new Intent(this,Myservice.class);
      stopService(i);
   }
  
   
}

myBroadcast.java

package com.ann;


import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.media.MediaPlayer;
import android.sax.StartElementListener;
import android.widget.Toast;

public class myBroadcast extends BroadcastReceiver {
//MediaPlayer mp;
    @Override
    public void onReceive(Context context, Intent intent) {
        Intent sintent=new Intent(context,AlarmServiceActivity.class);
        sintent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(sintent);
        Toast.makeText(context, "Don't panik but your time is up!!!!.",
                Toast.LENGTH_LONG).show();

        context.startService(new Intent(context,Myservice.class));


}
 }

Myservice.java


package com.ann;

import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.IBinder;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

public class Myservice extends Service {
    MediaPlayer mp;

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }
    public void onCreate(){
        mp=new MediaPlayer();
        mp=MediaPlayer.create(this, R.raw.roja);
        //mp.setLooping(false);
       
    }
    @Override
    public void onStart(Intent intent, int startId) {
        // TODO Auto-generated method stub
        try{
        Toast.makeText(this, "My service started ",Toast.LENGTH_LONG).show();   
        Log.w("inside","onStart");

        mp.start();
        }catch(Exception e){}
    }
    @Override   
    public void onDestroy() {   
        Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
        Log.d("inside", "onDestroy");
        mp.stop();
        }   
    
}
}


AndroidManifest.xml 


<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.ann"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".AlarmServiceActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service android:name="Myservice"></service>
        <receiver android:name="myBroadcast"></receiver>
    </application>

</manifest>