What is android permissions and security

Android Security : 

• Android Applications installs with unique Group Id
• each Android application is started in its own process
• Each application's file is private to this user, Other applications cannot access this files
• Every android applications are isolated from other running applications

Android Permissions: 

• Android operating system has permission Model
• Android apps must be required few permissions Example: camera, internet, contacts etc,
• permissions we can define on manifest file and java file 

Permissions before API level 23: 

• before API level 23 we need to ask persimmons before installing an app or application 
• if user denied the permissions applications cannot install, the user must grant all permissions 
• permissions cannot be denied after installations of an app.

Android Runtime Permissions: 

• API level 23 onwards introduced runtime permissions, 
• target level 23 onwards we need to define runtime permissions on the app
• we have two types of permissions Levels those are normal and dangerous permissions. 

Normal permissions:

Normal permissions are harmless for user Privacy or Operations of other applications 

Example: internet permissions, etc

Dangerous permissions: 

these permissions are harmful to user Privacy, example: contacts details ets.

int permissionCheck = ContextCompat.checkSelfPermission(Activity_Persmissions.this,
        Manifest.permission.WRITE_CALENDAR);
if (ContextCompat.checkSelfPermission(Activity_Persmissions.this,
        Manifest.permission.READ_CONTACTS)
        != PackageManager.PERMISSION_GRANTED) {

    // Should we show an explanation?    if (ActivityCompat.shouldShowRequestPermissionRationale(Activity_Persmissions.this,
            Manifest.permission.READ_CONTACTS)) {

        // Show an explanation to the user *asynchronously* -- don't block        // this thread waiting for the user's response! After the user        // sees the explanation, try again to request the permission.
    } else {

        // No explanation needed, we can request the permission.
        ActivityCompat.requestPermissions(Activity_Persmissions.this,
                new String[]{Manifest.permission.READ_CONTACTS},
                MY_PERMISSIONS_REQUEST_READ_CONTACTS);

        // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an        // app-defined int constant. The callback method gets the        // result of the request.    }