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Why my android application is exiting when I press the Back key

I am developing a small application at the moment it consists on 3 Activities.
Now when I start my application it starts fine and I can navigate from activity1 to activity 3 properly and without any problem.
Activity1-->Activity2--->Activity3
The problem comes that when I press the back button of my mobile device to go back to activity2, the application simply closes.
Can somebody please suggest how to figure it out what is happening.
that is how i am going to Activity2 from Activity2
Intent activity3 = new Intent(Activity2.this,Activity3.class);
Activity2.this.startActivity(activity3);
Activity2.this.finish();
Note:I am not using emulator I am using mobile and doing all the debugging directly on the mobile.
Thanks

This is because you are calling the finish() function which removes the activity from the stack. Remove the line Activity2.this.finish(); and you should be going back the way you wanted.

Because you call finish() method.
Due to this from activity stack your last activity is removed so that's way your current activity is finished on backPressed().
To overcome this You must remove
Activity2.this.finish();
from your code.

Activity Process

I have 4 activities. A,B,C and D.
From each activity user can start any activity.
i.e. Activity A has 3 buttons to start B,C and D. In same way all other activities also has 3 buttons.
Now my question is If user go in this sequence A->B->C->B.Now If user press back button then this sequence happens. B->C->->B->A. I want to change in this way B->->C->A. how can i do this?

I don't clearly understand your question, but maybe try use:
android:launchMode="singleInstance"
You want to keep the same instance all the time, not create a new one, yes?

finish activity B using finish() when you moved in the forward direction that means A>B(finish())>C>B

Like #Krishnakant said you need to add finish(); everytime, As far as I'm aware the back button is called as the Achille's heel for android programming as coding or adding handlers to it is not easy.

use intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT); before staring any activity.

how do i close a specefic activity and get to previous activity Programatically?

Here i have a few activities that consist different menus in my app..
The problem is that i want to add a are you sure popup box to exit the current menu and return back but calling finish() method on the click event of yes button of popup box causes all activities to terminate and app exits...
I want to make a way to terminate only the foreground activity and
return to last activity programatically (i.e without using back key)

Can u post some source code regarding how you start you new activities? Are you starting multiple activities at all? finish() method only finishes the current activity and not the entire stack of activities, thus the system automatically brings to front the previous activity from the stack. I can't understand your question please provide some further details.

Android Multi-Screen Application

How do you handle multiple screens in an android application? I have developed with the tab bar at the bottom without problem, however what I am wanting to do is replace all the content on the screen with the content from a new .xml layout file I have created in the project. Additionally, how would I tie the back end code to the new layout file? I'm sure this question probably exists already and is googleable (may have made up a new word). However, I don't know exactly what it is that I am looking for. Thanks in advance for your help.

What you need to do is, create a new Activity and add it to the AndroidManifest.xml:
<activity android:name="ActivityClassName" android:label="Label for the Activity"></activity>
and can be called in a method:
public void startActivity() {
Intent someName = new Intent(CurrentClass.this, ActivityClassName.class);
startActivity(someName);
}

Android applications generally use a separate Activity for each screen, and switch between them using Activity.startActivity and Activity.startActivityForResult. You can pass arbitrary data to an Activity via Intent.putExtra.
Hope this helps,
Phil Lello

It really depends on how you want your application to flow.
Let's consider the scenario where a user does the following:
Starts your first activity
Presses the 2nd tab
Presses the 3rd tab
Presses the back button
If you use a separate activity for each screen, then the following would happen
Activity 1 is started
Activity 2 is started
Activity 3 is started
Activity 3 is closed, user returns to Activity 2
(in this case pressing the back button again would you take you back to Activity 1, and pressing it again would exit your application)
If you used one activity for all the tabs, then the following would occur
Activity 1 is started
Activity 1 sets tab content to tab 2 content
Activity 1 sets tab content to tab 3 content
Activity 1 is closed, user returns to home screen
If you are using a screen with tabs, then the second method (a single Activity with a TabHost or similar) is the preferred method, otherwise the user will end up making a large activity-stack just switching between tabs (meaning if they switch between tabs a lot they'll have to press the back button a lot of times to exit).
If you want to go for the single activity approach, then do some research on TabHost and TabContentFactory. In the createTabContent method of your factory you can inflate a View/layout from XML to set as the tab content using View.inflate. Look those up and come back ask another question if you get stuck ;)

i think you may want to play with more than one activity.... you can have multiple activities and one xml for each of them... in this way you can have different screens... check these links. Multiple Activities, Creating an Activity.... hope this helps...

android, starting and exiting activities

I have not really understood the handling of activities and the stack.
I have 3 activities, A - a splashcreen, B- a menu and C another Activity. I start the splash and exits it after a while when the menu is started.
In code I handle them all like this:
startActivity(new Intent(this, ContactInfoMenu.class));
finish();
Now, if I start the app and goes A-B-C, when I hit "Back" in C screen I jump back to B-the menu. Another "Back" exits the application, just like I want.
BUT .. if I go A-B-C-B-C - the "Back" button in C screen exits the whole app instead of getting me back to the B screen?
Why is that? It does like that in all my "subscreens", I can only enter them once, if I enter them a second time the "Back" button exits the app. And I have not tried to catch the "Back" action anywhere? Shouldn't I always call "finish()" when I start a new activity?
Regards

Finish is good for leaving the current activity and going back to the previous one. Otherwise, try to avoid calling finish() if you can help it.
There are a set of flags that you can pass when you start an activity that do a better job of determining how that activity behaves on the stack. These include:
FLAG_ACTIVITY_NO_HISTORY - your activity will not remain on the stack after another activity covers it.
FLAG_ACTIVITY_CLEAR_TOP - a good way to pop off a bunch of activities when you need to "go back" to a certain activity.
Many of these flags can be set in the manifest. Reading up on them will give you a better idea about "The Android Way".

Basically, You don't need to call finish() every time you go to another activity. If system is low on memory it will close your activity instance by itself.

finish() is more often used when yor are inserting some information in one page and then moving on to some other page. In that case, you might need to fininsh your first activity.
But in case where you need to shuffle between views, you must not use a finish() function, because it will cause the whole application to finish.
Try using back button of your own in your views to shift between activities, where you can move to any other activity of your application or even to the Main Screen.