AlertDialog : An alert dialog box supports 0 to 3 buttons and a list of selectable elements, including check boxes and radio buttons. Among the other dialog boxes, the most suggested dialog box is the alert dialog box.

ProgressDialog: This dialog box displays a progress wheel or a progress bar. It is an extension of AlertDialog and supports adding buttons.

DatePickerDialog: This dialog box is used for selecting a date by the user.

TimePickerDialog: This dialog box is used for selecting time by the user.

Android is a stack of software for mobile devices which has Operating System, middleware and some key applications. The application executes within its own process and its own instance of Dalvik Virtual Machine. Many Virtual Machines run efficiently by a DVM device. DVM executes Java language’s byte code which later transforms into .dex format files.

Features of Android :

- Components can be reused and replaced by the application framework.
- Optimized DVM for mobile devices
- SQLite enables to store the data in a structured manner.
- Supports GSM telephone and Bluetooth, WiFi, 3G and EDGE technologies
- The development is a combination of a device emulator, debugging tools, memory profiling and plug-in for Eclipse IDE.

It is advisable to use container classes of the STL so that you don’t have to go through the pain of writing the entire code for handling collisions, making sure its working well, testing it repeatedly with an overhead of time consumption.

Suppose you have some data that has values associated with strings and its fields consist of grades> in this situation you can directly use hash table instead of having it created by yourself.

Type checking is the operation on which the arguments that can only be applied for.

Static type checking performs the type checking operation before the execution of the program. To perform this operation, the arguments, expressions, variables must be given a data type.

Dynamic type checking performs the type checking operation at the time of the program execution. To perform this operation, the arguments, expressions, variables must be given a data type.

- Inheritence permits code reusability. 

- Reusability saves time in program development. 

- It encourages the reuse of proven and debugged high-quality software which reduces the problems after a system becomes functional.

Access specifiers in C++ determines the scope of the class members.

Public: If a class member is public, it can be used anywhere without the access restrictions.

Private: if a class member is private, it can be used only by the members and friends of class.

Protected: If a class member is protected, it can be used only by the members and friends of class and the members and friends of classes derived from class.

Scope resolution operator allows a program to reference an identifier in the global scope that is hidden by another identifier with the same name in the local scope.

A Stack is a linear structure in which insertions and deletions are always made at one end i.e the top - this is termed as last in, first out (LIFO). Stacks are useful when we need to check some syntex errors like missing parentheses.