Using Static Variables in Android

Using static variables in Android

static fields are attached to the Class instance as a whole, which is in turn attached to the ClassLoader which loaded the class. the_instance would be unloaded when the entire ClassLoader is reclaimed. I am 90% sure this happens when Android destroys the app (not when it goes into the background, or pauses, but is completely shut down.)

So, think of it as living as long as your app runs. Is Singleton a good idea? People have different views. I think it's fine when used appropriately, myself. I don't think the answer changes much on Android. Memory usage isn't the issue per se; if you need to load a bunch of stuff in memory, that's either a problem or it isn't, regardless of whether you encapsulate the data in a Singleton.

Does android save static variables?

May This Help you:

Lets start with a bit of background: What happens when you start an application?


The OS starts a process and assigns it a unique process id and allocates a process table.A process start an instance of DVM(Dalvik VM); Each application runs inside a DVM.
A DVM manages class loading unloading, instance lifecycle, GC etc.

Lifetime of a static variable: A static variable comes into existence when a class is loaded by the JVM and dies when the class is unloaded.

So if you create an android application and initialize a static variable, it will remain in the JVM until one of the following happens:

1. the class is unloaded

2. the JVM shuts down

3. the process dies

Note that the value of the static variable will persist when you switch to a different activity of another application and none of the above three happens. Should any of the above three happen the static will lose its value.

For More Detail: Read the Answer of Samuh in this Link... Click Here

Android Studio static or non-static variables and methods

The static keyword in java is used for memory management mainly. We can apply java static keyword with variables, methods, blocks and nested class.
if we talk about static variable then we difine it as
The static variable can be used to refer the common property of all objects (that is not unique for each object) e.g. company name of employees,college name of students etc.

The static variable gets memory only once in class area at the time of class loading.

and if we talks about it uses:
when you want to share your variable or methods only single copy through out the class without creating different copy, you should use static.

Advantages
It makes your program memory efficient (i.e it saves memory).

When to use static variable and sharedpreference in android

You can use static when there is not huge amount of data in the application.
sharedpreference can be used if the data is more also and can be stored and retrieved as and when it is required.

Is it safe to use static class variables in an android application

I have seen passing references in StackOverflow that these might not be safe.

They are not "safe" insofar as your process will be terminated from time to time, wiping out your static data members (and your custom Application, for that matter). Hence, static data members are good for a cache and not much else.

Within that scope, they are "safe".

You just need to make sure that this data is either stored somewhere persistent (e.g., file) or otherwise can be regenerated once the process is terminated and later is started up again. This is no different than with Application.

However I've tried two different applications using the same class, and even when running both applications side by side on a Galaxy S3 in multi-window mode, the static class variables remain separate.

Correct. Those are separate processes, with separate copies of your class and objects.

Public static variables and Android activity life cycle management

If the process is killed then all static variables will be reinitialized to their default values.

So whatever value you have set in Activity A will not persist

Android: Does passing values through static variable cause securtiy issues?

You mean Intent can be said less secure than static variables?

Whenever you call startActivity(), startService(), bindService(), or sendBroadcast() on a Context, the Intent leaves your process, goes to a core OS process, and then goes to whatever process contains the component you are trying to work with. That includes cases where the component calling the method is in the same process as the component it is trying to work with. All else being equal, a static variable is more secure, in that it does not leave the process (unless you do that yourself).

As far as we know, Intent objects are secure against spies. However, there have been bugs in this area in the past, and I cannot rule out the possibility of bugs in the future.

from all application scope I meant static variables are shared and everybody inside application can see it

You are responsible for all of the code in your application, except for the framework implementation.

if an application have several process, static variables are shared among them

No.

or each process hold different instances of static variable?

Yes.

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