Creating Alert dialogue boxes in Android:

public class ButtoneventActivity extends Activity implements View.OnClickListener {

    /** Called when the activity is first created. */

                private Button b1;

                private Button b2;

                private Button b3;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        b1=(Button)findViewById(R.id.button1);

        b1.setText("Click");

        b1.setOnClickListener(this);

        b2=(Button)findViewById(R.id.button2);

        b2.setText("alert");

        b2.setOnClickListener(this);

        b3=(Button)findViewById(R.id.button3);

        b3.setText("Conform");

        b3.setOnClickListener(this);

    }

                @Override

                public void onClick(View view) {

                                // TODO Auto-generated method stub

                                if(view==b1){

                                                AlertDialog showAlert=new AlertDialog.Builder(this).create();

                                                 showAlert.setTitle("it's clicked");

                                                 showAlert.setMessage("are you sure you want to Burn?");

                                                 showAlert.setButton("Burn",new OnClickListener(){

                                                                @Override

                                              public void onClick(DialogInterface dialog, int which) {

                                                                   // TODO Auto-generated method stub

                                                                                dialog.cancel();

                                                                }                                                             

                                                  });

                                                 showAlert.show();                         

                                        }

                                else if(view==b2){

                                               AlertDialog showAlert=new AlertDialog.Builder(this).create();

                                                 showAlert.setTitle("Button clicked");

                                                 showAlert.setMessage("are you sure you want to save?");

                                                 showAlert.setButton("save",new OnClickListener() {

                                                                @Override

                                                 public void onClick(DialogInterface dialog, int which) {

                                                                    // TODO Auto-generated method stub

                                                                                 dialog.cancel();

                                                                }       

                                       });

                                                 showAlert.setButton2("Cancle",new OnClickListener(){

                                                                                @Override

                                            public void onClick(DialogInterface dialog, int which) {

                                                                  //TODO Auto-generated method stub

                                                                                                 dialog.cancel();

                                                                                                                                                                                                       

                                       }                                 

                             });

                                                 showAlert.show();

                                }

                                else if(view==b3){

                                                AlertDialog showAlert=new AlertDialog.Builder(this).create();

                                                 showAlert.setTitle("Button clicked");

                                                 showAlert.setMessage("are you sure you want to save?");

                                                 showAlert.setButton("Yes",new OnClickListener(){

                                                                @Override

                                                  public void onClick(DialogInterface dialog, int which) {

                                                                        // TODO Auto-generated method stub

                                                                                 dialog.cancel();

                                                                }               

                               });

                                                 showAlert.setButton2("NO",new OnClickListener(){

                                                                                @Override

                                                      public void onClick(DialogInterface dialog, int which) {

                                                                               // TODO Auto-generated method stub

                                                                                                 dialog.cancel();               

                                                                                }     

                                                           });

                                                 showAlert.setButton3("Cancle",new OnClickListener(){

                                                                                @Override

                                     public void onClick(DialogInterface dialog, int which) {

                                                                // TODO Auto-generated method stub

                                                                                                 dialog.cancel();

                                                                                }      

                                        });  

                                  showAlert.show();   

                                               }

                             }

    }

Passing Data from One Intent to Another Intent:

Here I used two Activity classes to pass data from one activity to another activity through Intents.

Main Activity.java :  which Intent send the data:

public class MainActivity extends Activity implements OnClickListener {

     EditText name, pwd;

                Button sub;

                @Override

                protected void onCreate(Bundle savedInstanceState) {

                                super.onCreate(savedInstanceState);

                                setContentView(R.layout.main);

                                name=(EditText)findViewById(R.id.NameText);

                                pwd=(EditText)findViewById(R.id.PassWordText);

                                sub=(Button)findViewById(R.id.button1);

                                sub.setOnClickListener(this);

                }

                @Override

                public void onClick(View v) {

                                String ename=name.getText().toString();

                                String epwd=pwd.getText().toString();

                                Intent intn=new Intent(MainActivity.this,SecondActivity.class);

// here putExtra(keyvalue,value); // here keyvalue is a key value to identify value from first intent in another intent. Value is value which you are passing to another intent.

                                intn.putExtra("Name",ename);

                                intn.putExtra( "PassW",epwd);

                                startActivity(intn);

                }       }

Second Activity.java: which receives that data and prints that data:

public class SecondActivity extends Activity implements OnClickListener{

                Button get,search;

                EditText nm,pw;

                String sname,spwd;

                @Override

                protected void onCreate(Bundle savedInstanceState) {

                                super.onCreate(savedInstanceState);

                                setContentView(R.layout.second);

                                get=(Button)findViewById(R.id.button);

                                nm=(EditText)findViewById(R.id.editName);

                                pw=(EditText)findViewById(R.id.editPassWord);

                                search=(Button)findViewById(R.id.Searchbutton);

                                search.setOnClickListener(this);

                                get.setOnClickListener(this);

//Bundle is using to get the intent extra fileds from passing intent.

                                Bundle b=getIntent().getExtras();

                                sname=b.getString("Name");

                                spwd=b.getString("PassW");

                }

                @Override

                public void onClick(View v) {

                                // TODO Auto-generated method stub

                                if(v==get){

                                nm.setText(sname);

                                pw.setText(spwd);

                                }

                                else if(v==search){

                                                Intent intn=new Intent(Intent.ACTION_VIEW);

                                                intn.setData(Uri.parse("http://www.google.com"));

                                                startActivity(intn);

                }              }               }

Transient and Volatile Variable in JAVA

Transient variable: the class level variable that has transient keyword in its definition is called transient variable. Local variable cannot be declared as transient. It leads to CE: illeagal start expression.

We declare variable as transient to tell to JVM that we do not want to store variable value in a file in object serialization. Since local variable is not part object, declaring it as transient is illegal. For more details on object serialization and transient variable refer IOStreams concept.

Class example {

Static transient int x=10;

Transient int y=20;

}

Volatile variable: the class level variable that has volatile keyword in its definition is called volatile variable. . Local variable cannot be declared as volatile. It leads to CE: illeagal start expression.

We declare variable as volatile to tell to JVM that we do not want to modify variable value concurrently by multiple threads. If we declare variable as volatile multiple thread are allowed to change its value in sequence one after one.

Class example {

Static volatile int x=10;

Volatile int y=20;

}