Week 1-6

Question 1

What is machine code?

Answer 1

Low level hexadecimal instructions

Question 2

What is assembly language?

Answer 2

Low-level programming language with symbols for instructions.

Question 3

What is high level programming language?

Answer 3

Easier to understand. Translated to machine code by compiler.

Question 4

Explain life-cycle of a C-file?

Answer 4

Starts as basic text file.
Compiler takes C file and produces an executable.
When we execute loaded into memory.
CPU executes.

Question 5

What are the problems with machine code?

Answer 5

Computer systems are different.
OS provide different libraries
Different CPUs cannot execute the same program and have different instructions
Programs must be compiled again for the different CPU types.

Question 6

Why do we download different versions of software for each OS?

Answer 6

Cause each OS has different libraries and code must be compiled differently for each.

Question 7

What is the advantage of JVM?

Answer 7

Write code once, run on any OS?

Question 8

What is a java program compiled to?

Answer 8

bytecode

Question 9

Why do we not need dynamic memory allocation?

Answer 9

JVM garbage collector frees memory automatically.

Question 10

What does IDE stand for?

Answer 10

Integrated Development Environment

Question 11

When we perform calculations with different typing in java, what type does the result take?

Answer 11

The longest type.

Question 12

What is autoboxing and unboxing?

Answer 12

A: Primitive type converted to wrapper object. E.g. Integer i = 4;
U: Wrapper object converted to primitive type. int i = intObj;

Question 13

Syntax for array declaration in java.

Answer 13

int[] numbers = new int[size];

Question 14

Syntax to get length of array test.

Answer 14

test.length

Question 15

Syntax for ArrayList.

Answer 15

ArrayList<TYPE> array = new ArrayList<TYPE>();</TYPE></TYPE>

Question 16

What is OOP?

Answer 16

Is based on the concept of objects which can encapsulate both data and behavior. Designed to model real-world entities and their interactions.

Question 17

What is cohesion?

Answer 17

Programs are broke up into classes. Classes contain related functionalities. The more related the higher the cohesion.

Question 18

Difference between object and class.

Answer 18

Class is an idea. E.g. idea of a ‘chair’
Object is an instance of idea, real thing.

Question 19

What is a default constructor?

Answer 19

Constructor with no parameters, that initializes instance variables to their default values.

Question 20

T or F. We can have more than one constructor.

Answer 20

True.

Question 21

What does a constructor implicitly return?

Answer 21

A reference to where the object is in memory.

Question 22

How does copying a primitive differ from copying an object in java?

Answer 22

If I copy a primitive, a whole new copy is made in memory, so changing the copy won’t affect original.

If I copy an object, a reference is all that is copied, so if I edit the copy, the original will also be affected.

Question 23

Syntax for default constructor.

Answer 23

public Name() {

}

Question 24

Main syntax.

Answer 24

public static void main(String[] args) {
}

Question 25

What does a constructor explicitly return?

Answer 25

A constructor does not return any value, not even void

Question 26

What does API stand for?

Answer 26

Application Programmer Interface

Question 27

Syntax for enums.

Answer 27

enum type {Coffee, Biscuits, Milk}; private type t; Object o = new Object(type.Milk);

Question 28

Define encapsulation.

Answer 28

The process of hiding implementation details inside a class, but allowing methods to be accessed.

Question 29

Explain visibility access levels.

Answer 29

Same class (public, protected, default, private) Same package (public, protected, default) A subclass (public, protected) Anywhere else (public)

Question 30

Give the visibility things in order of decreasing security.

Answer 30

private default protected public

Question 31

What is an immutable class?

Answer 31

A class without a mutator (setter) method.

Question 32

What is a class variable? Syntax for a class variable.

Answer 32

A variable shared among all instances of a class. static int name = 1;

Question 33

Syntax for constant.

Answer 33

public static final int CONSTANT = 0;

Question 34

Why would a static method be used? What are their features?

Answer 34

For a utility role. Cannot use instance variables and not connected to objects but still call with class name.

Question 35

What are the only variables that can be used by static methods?

Answer 35

static variables.

Question 36

Explain static imports using Math as an example.

Answer 36

import static java.lang.Math.*; means that we can call sqrt() without doing Math.sqrt();

Question 37

What are singleton variables?

Answer 37

Special case of static class variables. Is an object that we need only one instance of.

Question 38

Syntax for interface.

Answer 38

public interface InterfaceName { }

Question 39

T or F. An interface can also provide method implementation without any extra syntax.

Answer 39

False.

Question 40

T or F. A class that implements an interface must override all abstract methods of the interface.

Answer 40

True.

Question 41

T or F. All methods in an interface are public.

Answer 41

True

Question 42

What is polymorphism?

Answer 42

Means classes can implement the same methods differently even if part of the same interface.

Question 43

What are default methods in java?

Answer 43

Allow method implementation within an interface in java by placing keyword default in front.

Question 44

T or F. You can override the visibility of a method being overwritten from implemented interface.

Answer 44

False.

Question 45

T or F. You can instantiate an interface.

Answer 45

False.

Question 46

How is inheritance defined?

Answer 46

extends keyword

Question 47

If a subclass inherits a private variable what happens?

Answer 47

The variable exists but cannot be accessed or changed.

Question 48

What is the default superclass?

Answer 48

Object

Question 49

T or F. If A extends B and we cast A to B. What methods can be accessed?

Answer 49

Only the methods of B

Question 50

Syntax for calling superclass constructor.

Answer 50

super(parameters);

Question 51

Syntax for running superclass function.

Answer 51

super.functionName(parameters);

Question 52

Overriding equals syntax.

Answer 52

public boolean equals (Object obj){ if (obj instanceof BankAccount){ BankAccount b = (BankAccount) obj; return b.accountNumber == this.accountNumber; } else { return false; } }

Question 53

How does inheritance work with interfaces?

Answer 53

Simply adds more requirements for class that implements subclass.

Question 54

What is the difference between an abstract class and an interface?

Answer 54

Abstract classes can contain instance variables. Abstract classes are implemented with extends

Question 55

Syntax for abstract class.

Answer 55

public abstract class AbstractShape { }

Question 56

What is a final class?

Answer 56

A class that cannot be extended.

Question 57

What is a final method?

Answer 57

A method which cannot be ovverriden.

Question 58

What must be done to a method called it within a constructor?

Answer 58

It must be declared as final.