Programming 2

Question 1

Difference between a byte-based stream and character-based stream.

Answer 1

Byte-based uses InputStream and OutputStream.
Character-based uses a Reader and Writer.

Question 2

Steps for a Java I/O operation

Answer 2

Get a file ready with the File class
Set up a Stream
Using Read or Write
Close the Stream

Question 3

Byte-based vs Character-based

Answer 3

Byte-based
Uses InputStream and OutputStream.
Setting up the stream creates a new file if one doesn’t already exist.
New line with \r\n
Best for raw data, e.g. mouse and keyboard.

Character-based
Uses Reader and Writer.
Creates a new file, or overwrites an existing one.
Best for pure text.

Question 4

ByteArray Stream

Answer 4

Reads and writes directly into memory.
Normally used for generating temporary data.

Question 5

Pipeline stream

Answer 5

Mainly used for communicating and connecting between threads.

Question 6

Object serialisation

Answer 6

Used to store objects to the disk so they can be written to a data stream.
Only properties are serialised.
Done with an ObjectOutputStream.

Question 7

Object deserialisation

Answer 7

Used to unflatten an object when pulling it off the disk.
Done with ObjectInputStream.

Question 8

Object versioning

Answer 8

A serialised object has a hash of the object’s class written as part of its state when serialised.
During deserialisation, the serial version UID is compared to the existing classes, and if they don’t match the deserialisation fails and it results in an InvalidClassException.

Question 9

Requirements for serialisation

Answer 9

An object can be serialised if:
All the fields are primitives or Strings.
Any class referenced in variables are also declared as Serializable.
(Ignoring static properties)

Question 10

Types of String comparisons

Answer 10

Double equals (==)
Checks if the variables point to the same String in the heap.
.equals()
Checks if the variables have equal values.

Question 11

Verification vs Validation

Answer 11

Verification: testing software correctly implements a specific function.
Validation: testing software satisfies customer requirements.

Question 12

White-box vs Black-box testing

Answer 12

White-box: using known inputs and outputs.
Black-box: used to test without knowledge on the internal workings of the software.

Question 13

Unit testing

Answer 13

Includes:
Identifying the code to be tested in isolation.
Developing a suite of test cases.
Writing a test harness for each case.

White-box testing done by developers.

Question 14

Integration testing

Answer 14

Repeatedly testing the combination of larger collections of code units.

A mix of white- and black-box testing done by testers.

Question 15

System testing

Answer 15

Testing the entirety of the system.

Black-box testing done at the end of development.

Question 16

Testing in isolation

Answer 16

If a class depends on another, a ‘fake’ subclass of the required class is made, a mock or stub object.

Question 17

A stub object

Answer 17

Passes data to the main program being tested in isolation.
Often uses hard-coded values for simplicity.

Question 18

A driver object

Answer 18

A fake main program that accepts test case data and passes it on to the components being tested.
Used to fulfil requirements of missing or incomplete components.

Question 19

Types of integration testing

Answer 19

Top-down
Bottom-up
Sandwich
Big Bang

Question 20

Top-down itegration

Answer 20

Tests the high-level moules in isolation with stub dependencies.
Adds in the actual modules being called and tests them together.
Repeats until all modules are included.

Question 21

Bottom-up integration

Answer 21

Tests the low-level moules in isolation.
Adds in the modules that call this module and tests them together.
Repeats until all modules are included.

Question 22

Sandwich integration

Answer 22

Identifies the top, middle, and bottom layers.
The top is tested with Top-down integration, the bottom with Bottom-up integration. Then the middle is included.

Question 23

Big Bang integration

Answer 23

Non-incremental, in which each unit is tested thoroughly in isolation.
Then the whole system is integrated and tested together at once.

Question 24

JVM

Answer 24

Java Virtual Machine

Question 25

WORA

Answer 25

Write Once, Run Anywhere

Question 26

Class loader and Method area

Answer 26

The class loader locates .class files, verifies them through their bytecode
Then loads them into the method area in the shared memory.

Question 27

Machine’s memory architecture

Answer 27

Comprised of:
Shared memory, one heap and one method area per JVM instance.
Private memory, one java stack and program counter per thread.

Question 28

Program Counter

Answer 28

Holds the address of the next bytecode instruction to execute, for each thread.

Question 29

Java stack

Answer 29

Holds state information for the thread.
E.g. which methods have been called, local variables, parameters, and used for performing calculations.

Question 30

Execution engine

Answer 30

The part of the JVM which describes how bytecode is executed, and what the expected behaviour should be. Done in terms of the JVM instruction set.

Question 31

The Heap

Answer 31

Located in the shared memory.
Stores object instances, the values of all non-static fields.
Can be primitives or references/pointers to other instances in the heap.

Non-primitive data are stored as their own object instance.

Question 32

Stack frame

Answer 32

When a thread calls a method, a new frame is pushed onto the thread’s Java stack. All local variables, parameters, and temporary calculations are done within this frame.

Question 33

Recursion

Answer 33

Defining an entity in terms of itself, e.g. a method calling itself, or a list containing a list.

Question 34

Defining a pointer in C for a primitive or array variable

Answer 34

Primitive variable:
*pointer = &var
Array variable:
*pointer = array
*pointer = &array[0]

Question 35

Accessing a pointer in C

Answer 35

Access to the memory location: *pointer
Access to the memory address: pointer