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Android startActivity(intent) doesn't finish current activity, but runs all the code from current activity

I have a section of code where I want to go to another activity. After parsing these lines of code, the app doesn't close current activity but keeps executing all the onCreate() method from the current activity.
Intent intent = new Intent(ExtraInformationActivity.this,
MainActivity.class);
startActivity(intent);
finish();
Should the finish() function immediately finish current activity and go to the new activity, or the app should execute all the code from the onCreate method? How can I immediately close current activity? Thanks

Calling finish() in an activity does not INSTANTLY close it, it will close it after it runs all of the lifecycle methods and whatever method you called finish() from.
So if you call finish() in onCreate, it will still call onStart, onResume, onPause, onStop and onDestroy (and all of the regular lifecycle methods).
That is how it works, and you can't change that. So you'll need to adjust your code to it.

to avoid running codes after calling finish, add return; after finish();
Read this
void finish () Call this when your activity is done and should be
closed.

When you are using startActivity(), there is no need to use finish().New activity automatically pops-up.

why onCreate() is called every time when its started activity is finished?

In my app, there is a activity A, which it's a main activity, also there are several fragments inside A. When you click the images in one of fragments, it will start a new Activity B. When you click back button, i will call finish() to finish the activity and return to Activity A. But when returning to the Activity A, onCreate() of A is called again. Why onCreate() is called each time? As i know, it should be just called once, and then onStart() should be called.
From segment to the Activity B is as below:
Intent i = new Intent(_scontext, ProductListing.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
_scontext.startActivity(i);
getActivity().overridePendingTransition(R.anim.push_out_to_left,R.anim.push_out_to_right);
When click back button in the Activity B, the code snippet is as following:
Intent _gobck = new Intent(_ctx,ProductDisplay.class);
startActivity(_gobck);
finish();
overridePendingTransition(R.anim.push_out_to_left,
R.anim.push_out_to_right);
What's wrong with the code? Am i missing anything?

You are starting the activity again. Remove the following code and it will work.
Intent _gobck = new Intent(_ctx,ProductDisplay.class);
startActivity(_gobck);

Since you already got your answer by #Rajitha Siriwardena but i just want to clear some of the points here,
As i know, it should be just called once, and then onStart() should
be called.
Above sentence is not a true first of all .
There is possibility to for your ActivityA to go in OnCreate even if you finish your ActivityB. If your ActivityB stay in foreground for a long time ,of-course your ActivityA will be in background in that case , so ultimately your Activity in onStop (remember not in onPause) and android Activity life cycle doc says, after onStop if your app want reach your Activity then it will goes in onCreate
So finish() ActivityB would work but there is no guarantee to your ActivityA called onCreate when you do so .

if you remove finish() from your backPress Activity will not be created and you don't need to write Intent it will manage it's back stack it self.

onCreate called despite using FLAG_ACTIVITY_REORDER_TO_FRONT

I have 2 activities (A and B) and they have 2 buttons to switch between.
A oncreate
B oncreate
A oncreate
A onresume
what I wanted to do is after sending intent from B to A oncreate should not be called but at this point it does. To overcome that I found FLAG_ACTIVITY_REORDER_TO_FRONT (from here) and thought it could called only onresume but it didn't.

FLAG_ACTIVITY_REORDER_TO_FRONT does exactly what you think it should do. However, if you start ActivityA and then ActivityA starts ActivityB and calls finish() on itself, then when ActivityB starts ActivityA with an Intent that has FLAG_ACTIVITY_REORDER_TO_FRONT there will be no instance of ActivityA to bring to the front. In this case Android will simply create a new one. I can only assume that is what you are seeing.

FLAG_ACTIVITY_REORDER_TO_FRONT changes activity history. If the requested activity is found in the history of previously visited activities (in a task), the older history record for this activity is cleared. So, while pressing back button, user will not encounter this activity in a task.
This flag won't affect the call to onCreate(), If activity does not exists in the task (not loaded or destroyed), onCreate() will be called to create it.

You can't just cancel onCreate. If B is full screen activity android can kill A activity and will recreate it when you try to restart it with FLAG_ACTIVITY_REORDER_TO_FRONT flag and call it's onCreate method. If Activity A will be still alive at the monent when you try to bring it to front, onCreate method should not be called.
Maybe in your case you should try to use fragments?

OnCreate instead of OnResume/OnRestart?

I have some Activities, let's say Activity A, B and C.
In the Activity A I call the B through a Menu with an onOptionsItemSelected:
Intent main = new Intent (this, MainActivity.class);
this.startActivity(main);
Now, when I'm in the B activity, I can call the A one back in the same way (with Intent and startactivity): how can i handle it to call the OnResume or the OnRestart method of A instead of the OnCreate one?
I'm logging it and anytime I move from an activity to another one, it always call the OnCreate method: what can I do?

Configure your Activity A as "singleTask" or "singleInstance" in the manifest.xml. Then Acitivity A's onResume() will be fire instead of onCreate() when you call Activity A from Activity B (assuming Activity A was already instantiated like you describe). There are drawbacks to this kind of configuration so read this.
example manifest:
<activity android:name=".YourActivityA"
android:configChanges="keyboardHidden|orientation"
android:launchMode="singleTask">

You cannot control whether the OnCreate/OnResume/OnRestart methods are called directly. It is based on whether the previous activity is still in memory or not.
http://developer.android.com/guide/components/activities.html
http://developer.android.com/images/activity_lifecycle.png

I'm logging it and anytime I move from an activity to another one, it always call the OnCreate method: what can I do?
To return to Activity A from Activity B, if you use:
startActivity(), then A's onCreate() will always be called.
finish(), then A's onCreate() may or may not be called. (It depends on whether A was destroyed by you or the OS.)

Issue with activity called with Intent.FLAG_ACTIVITY_CLEAR_TOP

I want to finish my app calling the first activity with Intent.FLAG_ACTIVITY_CLEAR_TOP and finishing it. However, when it finishes, the app restarts automatically, and goes directly to Activity 2.
Why? Isn't the stack of activity supposed to be empty after finishing an activity called with Intent.FLAG_ACTIVITY_CLEAR_TOP?
My stack is Activity2>(more activities)>Activity1.
In Activity2
Intent exit_intent=new Intent(context, Activity1.class);
exit_intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
exit_intent.putExtra("EXIT", true);
context.startActivity(exit_intent);
In Activity1
if (getIntent().getBooleanExtra("EXIT", false)) {
finish();
}

From the javadoc:
If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.
CLEAR_TOP will wipe out all Activities ABOVE Activity1: if Activity2 is below Activity1 then once Activity1 finishes you will see Activity2.

Are you sure finish() is being called properly in Activity1? I'm getting the feeling it's not, because:
I'm not sure where that if statement goes inside your Activity. It should be in onNewIntent.
If you are making that if statement inside the onNewIntent method, it's still wrong. The docs specify that getIntent() will always return the original intent that started the Activity, unless you call setIntent().
To conclude, maybe something else is getting called in your Activity1 (can't tell without the full code) that starts Activity2 instead of finishing.
If what I described is not the case, and your activity stack indeed looks like Activity2 > Activity1 like the others have described yes, it will not work. Just call finish() in Activity2?

According to the docs:
If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.
So it doesn't clear the entire activity stack, only any other activities that were on top of an old instance of the activity being launched.

You have it right but are you catching the intent inside onNewIntent method of your first activity? also activity 2 should be launched after activity 1 in order for this to work.

From Intent doc:
public static final int FLAG_ACTIVITY_CLEAR_TOP
If it has declared its launch mode to be "multiple" (the default) and you have not set FLAG_ACTIVITY_SINGLE_TOP in the same intent, then it will be finished and re-created.