krishnachary

java technical questions

2012-06-18T11:55:00.001+05:30

1.
public class Example1 {
int i=1000;
public static void main(String[] args) {
System.out.println("Mr. "+args[1]+"get salary "+i);
//compile time error:saying
//non static variable i can not be referenced from static area

}

}

2.class Base
{
public void m1()
{

}
}
class Example2 extends Base{
protected void m1()//m1() in Example2 can not m1() in Base
//attempting to assign weaker access privileges;was public
{

}

}

3.class B
{
final private void m1()
{

}
}
class Example3 extends B{
void m1()
{
//no error because private methods are not inherited
}

}

4.public class Example4 {
public static int m1(boolean b)
{

try
{
if(b)
{
return 1;
}
return 0;
}
finally
{
System.out.println("om sai");
}

}
public static void main(String[] args) {
m1(true);
}
//output: om sai

}

5.public class Example5 {

Example5() {
this(10,10);
//consrtuctor Example5 in class Example can not be applied to given types
//required: no argument
//found:int,int
}
public static void main(String[] args) {
Example5 e=new Example5();

}

}

6.class Ba
{
void fr(int x)
{
if(x>10)
{
System.out.println("super : "+x);
}
else
fr(++x);

}
}
class Example6 extends Ba{
void fr(int x)
{
if(x>10)
{
System.out.println("sub : "+x);
}
else
super.fr(x);

}
public static void main(String[] args) {
Example6 ex=new Example6();
ex.fr(10);
}

}
//output: sub 11

7.class Bas
{
void m1()
{
System.out.println("base class");
}
}
class Example7 extends Bas {
void m1()
{
System.out.println("derived class");
}
public static void main(String[] args) {

Example7 e=new Example7();
Bas b= (Bas)e;
b.m1();
}
//output:derived class
}

upto here perfect questions

last one just guess

8.public class Example9 {
int x;
public static void main(String[] args) {
int x=10;
Example9 e=new Example9();
e.m1(x);
System.out.println("x"+x);

}
public void m1(int y)
{
x=y*y;
}

}
//output: 10

android concepts and code

2012-06-11T15:26:00.001+05:30

http://androidmohan.blogspot.in/2012/06/android-concepts-and-code.html

Android Tools

2012-06-11T14:59:00.002+05:30

Android Tools

Emulator –

- Virtual Device

- Can develop test and debug apps

- Allows to run simultaneous apps

ADT – Android Development Tools

- Plugin for eclipse integrated development environment

- Increases speed and efficiency for developing android apps.

- Allows the apps to access DDMS tool from eclipse.

- Gives the wizard for basic new project creation.

DDMS – Dalvik Debug Monitor Service

- Works with the emulator or the mobile device

- Gives the information about the virtual devices and physical devices.

- Thread and Heap tab for easy display.

- Screen capture

- Exploring the files

- Causes Garbage collection

- Running Log cat

ADB – Android Debug Bridge

- Three core components

o Client

o Server

o Daemon – A computer program that runs in the background like a thread. Don’t have user control.

- Used to manage the state of an emulator or a device.

- Used to install any application directly from PC to mobile or emulator

- To manage SQLite DB.

AAPT – Android Asset Packaging Tool

- Used to package the .apk file

- Developers can use it directly to view , create and update .zip, .jar and .apk files.

AIDL – Android Interface Description Language

- Used for Inter process communication.

- Interface based. Saves developers time.

Sqlite3

- Allows to access the SQLite data files created and used by android apps

TraceView

- Provides a graphical viewer for execution logs saved by your app

MKSDCARD

- Helps you to create a disk image that you can use with the emulator

- Converts .class files to Android byte code.

ActivityCreator

- Creates basic files that the developer needs, when the developer not using Eclipse.

Hierarchy Viewer

- Gives the user interface to the projects and emulator

INSTALLATION

Required SWs

JDK 1.5 or higher

Eclipse 3.5 or higher

ADT Plugin for Eclipse

Android SDK.

Process

Install JDK and set path up to bin in to environment variables.

Extract Eclipse and open eclipse.exe file.

Then helpàinstall new SW à give path to ADT pluginàthen install ADT plugin.

Install Android SDK installer file. Then select the files and install.

Then go to Windowsà preferencesàAndroidà give path of Android SDK, up to the root folder of tools folder.

Then go to Windowsà Android SDK and AVD managerà Virtual Devicesà Create a new Virtual Device.

Now the Set up is completed.

Generate map key steps in android

2012-06-11T14:58:00.001+05:30

https://developers.google.com/maps/documentation/android/mapkey

c:\>keytool.exe -list -alias androiddebugkey -keystore "C:\android\debug.keystore" -storepass android -keypass android

MD5 Key .............................

https://developers.google.com/android/maps-api-signup?hl=en-US

Basic Android Terminal and ADB Shell Command List

2012-06-11T14:19:00.000+05:30

While rooting your Android Phone or installing custom ROM on your mobile or partitioning your android device to install applications, requires some android terminal command and ADB (Android Debug Bridge) shell command knowledge. Below is the list of some basic android commands that are being used on Android platform frequently and that every android user

must know.

Basic Android Terminal and ADB Shell Command List

1. How to open a cmd in Android Phone
Method 1: “Start” – “”Program”-” “Accessories” – “” Command Prompt ”
Method 2: “Start” – “” Run “, type cmd ENTER

2. How to restart Android Phone
When the phone and Computer is connected to the data cable, you can enter the following command

1	adb shell reboot === ENTER

3. Restart Android into Recovery Mode
With the data cable connected to your phone and computer, enter the following command

1	adb shell reboot recovery === ENTER

4. Convert back to ext2 partition
Restart the phone into Recovery mode, press “Alt + X” into the console. Open cmd and enter the following command

adb shell === ENTER

tune2fs-O ^ has_journal / dev/block/mmcblk0p2 === carriage return

e2fsck / dev/block/mmcblk0p2 === carriage return (optional, can be a problem area in section 2, when used)

5. Pulling applications from Android phone to computer

1 2	adb pull /system/sd/app app adb pull /system/sd/app-private app-private

6. Pushing applications back to android phone from the computer

1 2	adb push app /system/sd/app adb push app-private /system/sd/app-private

7. Delete existing apps on Android SD

1 2	adb shell rm -r /system/sd/app adb shell rm -r /system/sd/app-private

8. Repair gravity System or switch to screen
Sometimes frequent brushing of phone can cause gravity system or switch to screen failure. Just follow the steps below-
Restart the phone into Recovery mode, press “Alt + X” into the console
Open cmd and enter the following command

1 2	mount / data === carriage return rm / data / misc / akmd * / data / misc / rild * === ENTER

9. Ext2/ext3/ext4 formatted partition
Enter the following command in the cmd

adb remount === ENTER

adb shell === ENTER

rm-r / system / sd / * === carriage return

10. Remove/ system / app under the application
Under normal circumstances / system / app is not under an application. Use the following methods to remove these applications.
Open cmd and enter the following command

1 2	adb remount === ENTER adb rm / system / app / Stocks.apk === Enter

11. If the start Time is too Long
Just enter the following command in order to view the boot process.

1	adb logcat === ENTER

12. Through Terminal Partition SD card
It will erase everything on your SD card

$ su

# cd /data

# wget http://64.105.21.209/bin/lib/droid/sdsplit

# chmod 555 sdsplit

# /data/sdsplit -fs *size* (add -nc to the end for JFv1.5ADP)

13. From the Recovery Screen, send an update file to your SD card.

adb shell mount /sdcard

adb shell rm /sdcard/update.zip

adb push *filename* /sdcard/update.zip

14. Restoring a nandroid backup via Fastboot
Start command-prompt/terminal cd to the nandroid folder and enter following commands

fastboot erase boot

fastboot erase recovery

fastboot flash system system.img

fastboot flash boot boot.img

fastboot flash userdata data.img

fastboot flash recovery recovery.img

fastboot reboot

15. Clear Search History in Android

Search History is accounted for Mobile Memory. It can also leak your privacy information as well. Just follow the steps below to clear android history.

Steps are as follows:

1. Make sure your mobile phone has Root authority.
2. Open the super-terminal.
3. Enter the following command

1 2	su rm / data / data / com.android.vending / databases / suggestions.db

4. Exit Hyper Terminal and restart the phone.

If you have a good one to add please post it in comment section

ExampleOnTimePickerDialog

2012-06-07T15:18:00.001+05:30

public class ExampleontimepickerdialogActivity extends Activity {

/**Private members of the class*/
private TextView displayTime;
private Button pickTime;

private int pHour;
private int pMinute;

/** This integer will uniquely define the dialog to be used for displaying time picker. */
static final int TIME_DIALOG_ID = 0;

/** Callback received when the user "picks" a time in the dialog */
private TimePickerDialog.OnTimeSetListener mTimeSetListener =
new TimePickerDialog.OnTimeSetListener() {
public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
pHour = hourOfDay;
pMinute = minute;
updateDisplay();
displayToast();
}
};

/** Updates the time in the TextView */
private void updateDisplay() {
displayTime.setText(
new StringBuilder()
.append(pad(pHour)).append(":")
.append(pad(pMinute)));
}

/** Displays a notification when the time is updated */
private void displayToast() {
Toast.makeText(this, new StringBuilder().append("Time choosen is ").append(displayTime.getText()), Toast.LENGTH_SHORT).show();

}

/** Add padding to numbers less than ten */
private static String pad(int c) {
if (c >= 10)
return String.valueOf(c);
else
return "0" + String.valueOf(c);
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

/** Capture our View elements */
displayTime = (TextView) findViewById(R.id.timeDisplay);
pickTime = (Button) findViewById(R.id.pickTime);

/** Listener for click event of the button */
pickTime.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showDialog(TIME_DIALOG_ID);
}
});

/** Get the current time */
final Calendar cal = Calendar.getInstance();
pHour = cal.get(Calendar.HOUR_OF_DAY);
pMinute = cal.get(Calendar.MINUTE);

/** Display the current time in the TextView */
updateDisplay();

}

/** Create a new dialog for time picker */

@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case TIME_DIALOG_ID:
return new TimePickerDialog(this,
mTimeSetListener, pHour, pMinute, false);
}
return null;
}
}

=============== Xml file ===============

<?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" >

<TextView
android:id="@+id/timeDisplay"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Time will appear here after being selected"
android:textSize="30sp" />

<Button
android:id="@+id/pickTime"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change the time" />

</LinearLayout>

Dialog box examples

2012-06-07T14:07:00.000+05:30

An alert box with a single button
A dialog box with two buttons
A dialog box containing a list
A dialog box containing checkboxes

Note:

We will be using Android Platform 1.5 for developing our application.

To demonstrate how to create dialog boxes firstly we will be creating a basic application with four buttons and clicking on each of these buttons will display a different kind of dialog box. We will be using XML based layout for our Application's User Interface. Create a new Android project with the following properties -

Project Name - DialogBox
Name of the Application - Dialog Box
Package name - com.botskool.DialogBox
Activity Name - Dialog Box

There will be four buttons and a string as listed below -

information string
alert button (This button will be used to display an alert box)
yesno button (This will be used to display a dialog box with Yes/No buttons)
selectlist button (This will be used to display a dialog box which contains a list)
selectlistwithcheckbox (This will be used to display a dialog box which contains a list along with checkbox)

Copy the following code in DialogBox.java -

import android.app.Activity;

import android.app.AlertDialog;

import android.content.DialogInterface;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class DialogBox extends Activity implements OnClickListener{

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

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

/** We need to set up a click listener on the alert button */

Button alert = (Button) findViewById(R.id.alertbutton);

alert.setOnClickListener(this);

/** We need to set up a click listener on the yesno button */

Button yesno = (Button) findViewById(R.id.yesnobutton);

yesno.setOnClickListener(this);

/** We need to set up a click listener on the selectlist button */

Button selectlist = (Button) findViewById(R.id.selectlist);

selectlist.setOnClickListener(this);

/** We need to set up a click listener on the selectlistwithcheckbox button */

Button selectlistwithcheckbox = (Button) findViewById(R.id.selectlistwithcheckbox);

selectlistwithcheckbox.setOnClickListener(this);

}

public void onClick(View view) {

/** check whether the alert button has been clicked */

if (view == findViewById(R.id.alertbutton)) {

// Code here to display alert box

}

/** check whether the yesno button has been clicked */

if (view == findViewById(R.id.yesnobutton)) {

// Code here to display the dialog box with Yes/No button

}

/** check whether the selectlist button has been clicked */

if (view == findViewById(R.id.selectlist)) {

//Code here to display the dialog box containing a list.

}

/** check whether the selectlistwithcheckbox button has been clicked */

if (view == findViewById(R.id.selectlistwithcheckbox)) {

//Code here to display the dialog box with checkbox

}

Copy the following code in main.xml -

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

<TextView

android:layout_width="fill_parent"