Java

Front 1

What is the relationship between a class and an object?

Back 1

A class defines the structure and behaviour of all entities of a given type, an object is one instance of that type of entity

Front 2

How does a class model object state?

Back 2

State of an object defined in a class by the fields

Front 3

How does a class model state behaviour?

Back 3

Behaviour of an object defined in a class by the methods

Front 4

What is the purpose of the static keyword?

Back 4

Static members belong to the class instead of a specific instance

Only one instance of a static field exists

Front 5

What are the purpose of get and set methods?

Back 5

Get methods return the value of a field

Set methods set the value of a field

Front 6

What is the purpose of a constructor method?

Back 6

The constructor method is called to create a new class object

Front 7

What three tasks does the new operator conduct?

Back 7

Instantiates a class by allocating memory for a new object

Returns a reference to that memory

Invokes the object's constructor

Front 8

Given a class, can you identify its fields, constructors and methods?

Back 8

Field: private typeName;

Constructor: public className( typeName) { ... }

Methods: public getTypeName() { return typeName; }

Front 9

How does the use of private and public access modifiers assist encapsulation?

Back 9

The fields within the class are private, only the class needs to access them

The interface is public, allowing the user to access/modify the internal state

Front 10

What are the benefits of encapsulation?

Back 10

Encapsulation protects the data fields from unauthorised access

Also ensures that data fields are modified consistently

Encapsulation allows you to change the way data is stored without affecting the external use of an object

Front 11

What is the difference between a primitive and a reference type?

Back 11

Primitive types are basic types of data

Reference types are any instantiable class, as well as arrays

Front 12

What are the 8 primitive types?

Back 12

Byte, short, int, long, float, double, boolean, char

Front 13

Name some examples of reference types

Back 13

String, Scanner, Random, Die, int[], String[]

Front 14

Are generic parameters compatible with both types?

Back 14

No, only reference types

Front 15

What is meant by auto-boxing and unboxing?

Back 15

Auto-boxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes

If the conversion goes the other way, it's unboxing

Front 16

Could you implement a simple class based on a UML design?

Back 16

Top bar: class name

Middle bar: field names, types

Bottom bar: methods

Front 17

Can you identify and draw a composition relationship?

Back 17

Front 18

Can you identify and draw an aggregation relationship?

Back 18

Front 19

Can you identify and draw an inheritance relationship?

Back 19

Front 20

Given a short case study that identifies classes and their relationships, can you combine these concepts into a UML class diagram?

Back 20

Front 21

Given two classes, can you identify a superclass and a subclass?

Back 21

The subclass will always extend its superclass

Front 22

Can a subclass stop methods from being inherited?

Back 22

No, but there are ways around it

Making the relevant method in the superclass private

Or moving the method into the subclass

Front 23

What is the meaning of methods that are inherited?

Back 23

Inherited methods are those which are predefined from the superclass and passed down to the subclass

Front 24

What is the meaning of methods that are overridden?

Back 24

Overridden methods are those which are inherited form the superclass, but are redefined by the subclass

Front 25

What is the meaning of methods that are newly defined?

Back 25

The term "redefinition" isn't usually used with regards to Java methods - either override or overload

To overload in Java is to create two methods in the same class with the same name, but different signatures

Front 26

Are you familiar with the substitution principle?

Back 26

Substitutability is a principle in OO programming, stating that, in a program, if S is a subtype of T, then objects of type T may be replaced with objects of type S

Front 27

What is the difference between upcasting and downcasting?

Back 27

Up-casting is casting to a supertype

Down-casting is casting to a subtype

Front 28

If an object of type X is assigned to a variable of type Y, what are the implications in terms of the methods that can, and cannot be invoked?

Back 28

You can only use methods that would be defined in object X's interface

If you later decide to use a different implication of X, it is easy

Front 29

Do you understand the implications of making a method final?

Back 29

You can declare some, or all of a class' methods final

You use the final keyword in a method declaration to indicate that the method cannot be overridden by subclasses

Front 30

Can you describe the diamond problem that may arise if multiple inheritances were permitted?

Back 30

The diamond problem is an ambiguity that arises when two classes, B and C, inherit from A, and class D inherits from both B and C

The compiler gets confused as to which methods it should use

Front 31

Explain the purpose of the @Override annotation

Back 31

The @Override annotation is used to redefine methods for different classes

Front 32

Can you explain the purpose of the toString() method and its conventional formation?

Back 32

This method is inherited from the Object class, and defines how you print out an object in a string format

For example:

return "Person:[name: " + name + ", age: " + age + "]";

Front 33

Can you explain the purpose of the equals() method?

Back 33

They are used to test equivalence in objects

Front 34

Given a UML class diagram, can you write an overridden equals() method?

Back 34

@Override

public boolean equals(Object obj) {

if(obj == this)

return true;

if(obj == null || obj.getClass() != this.getClass())

return false;

Person guest = (Person) obj;

return age == guest.getAge() && name = guest.getName();

}

Front 35

What is the difference of testing equality using the equals() method or the == operator, and where are they both appropriately used?

Back 35

== compares memory addresses, equals() compares the values in the objects

Front 36

What is the default behaviour of the equals() method you inherit from Object?

Back 36

It is the same as the comparison operator; it compares memory addresses

Front 37

Can you explain the purpose of the compareTo() method?

Back 37

It is used for comparing two strings lexicographically

Each character of both strings is converted into a Unicode value, and so if both the strings are equal, it returns 0, else it returns a positive/negative value

Front 38

Given a UML class diagram, can you implement a compareTo() method?

Back 38

@Override

public int compareTo(Object that) {

if(this == that) return 0;

primitive numbers use >, <

booleans use &&, and (... && !...)

Other Objects use a comparison int, and the compareTo method recursively

Front 39

Would you be able to use the compareTo() method in a test class to compare objects?

Back 39

You can call the method to test two objects, that can be equal, to test equality

Front 40

Can you explain how compareTo() assists in sorting a list?

Back 40

It defines whether an object should be placed before or after another object, from whatever is returned from the method

Front 41

Why might you choose to declare an interface type and initialise this with a concrete class type?

Back 41

An interface gives you the ability to specify a set of behaviours that all classes implementing the interface will share in common

We can define variables and collections that don't have to know what kind of object they will hold

Front 42

Can you use informed decisions to identify an appropriate data structure to use?

Back 42

In class X, there is an ArrayList of type Y, which shows the aggregate relationship

X has many Y, stored in an ArrayList

Front 43

Can you implement some of the common methods that an aggregate class would contain, e.g. add, remove, size, etc - all via delegation?

Back 43

Kennel k = new Kennel();

Dog d1 = new Pug("Carlie");

Dog d2 = new Labrador("Rex");

k.addDog(d1);

k.addDog(d2);

System.out.println(k.getDogs());

Front 44

What enables an aggregate class to be used within a for-each loop

Back 44

The class must implement iterable, as well as a method that defines what it should iterate over

Front 45

Can you write a for-each loop?

Back 45

for(Module m : StudentProfile.getCourse().getModulesOnCourse())

System.out.println(m.toString());

Front 46

Can you outline the three components that make up a stream pipeline, with one or more example of each?

Back 46

A source - collection, array, generator function, I/O channel

Zero or more intermediate operations that return a new stream - filter, map, limit, etc.

A terminal operation that produces a non-stream result - forEach, count, anyMatch, etc.

Front 47

What is a functional interface?

Back 47

An interface that is defined with only a single abstract method

Front 48

What is a lambda expression?

Back 48

A lambda expression is an anonymous function that can be used to create delegates, or expression tree types

Front 49

Can you write basic functions using lambda expressions?

Back 49

Names.stream().filter(Name -> Name.length() > 5).forEach(System.out :: println);

Front 50

How do functional interfaces provide a basis for lambda expressions?

Back 50

A functional interface is a runnable block of code which can be the target of a lambda expression

Front 51

Can you explain how the Border Pane lays out its child nodes?

Back 51

Nodes can be placed in five regions - top, bottom, centre, left, right

If application doesn't need regions, there is no need to define it, and no space is allocated to it

Front 52

Can you explain how a Border Pane behaves when its container is resized?

Back 52

If the window is larger than the space needed for each region, the space is given to the centre node by default

If the window is smaller, the nodes may overlap

Front 53

Can you explain how the HBox lays out its child nodes?

Back 53

The HBox layout provides an easy way for arranging a series of nodes in a single, horizontal, row

Front 54

Can you explain how the HBox behaves when its container is resized?

Back 54

The padding property can be set to manage the distance between the nodes and the edges of the HBox

Spacing can be set to manage the distance between the nodes

Front 55

Can you explain how the VBox lays out its child nodes?

Back 55

The VBox layout is identical to HBox, except its nodes are laid out in a vertical column

Front 56

Can you explain how the VBox behaves when its container is resized?

Back 56

The padding property can be set to manage the distance between the nodes and the edges of the VBox pane

Spacing can be set to manage the distance between the nodes

Margins can be set to add additional space around the individual controls

Front 57

Can you explain how the StackPane lays out its child nodes?

Back 57

The StackPane layout places all of its nodes within a single stack, with each new node added on top of the previous node

Front 58

Can you explain how the StackPane behaves when its container is resized?

Back 58

The alignment property can be set to manage how children are positioned in a StackPane

This property affects all children, so margins can be set to adjust the position of individual children in the stack

Front 59

Can you explain how the Grid Pane lays out its child nodes?

Back 59

The Grid Pane enables you to create a flexible grid of rows and columns in which to lay out nodes

Nodes can be placed in any cell, and can span cells as needed

Front 60

Can you explain how a Grid Pane behaves when its container is resized?

Back 60

Gap properties can be set to manage the spacing between rows and columns

The padding property can be set to manage the distance between the nodes and the edges of the grid

Front 61

Can you explain how the Flow Pane lays out its child nodes?

Back 61

The nodes within a Flow Pane are laid out consecutively and wrap at the boundary set for the pane

Nodes can flow vertically or horizontally

Front 62

Can you explain how a Flow Pane behaves when its container is resized?

Back 62

Gap properties can be set to manage the spacing between the rows and the columns.

The padding property can be set to manage the distance between the nodes and the edges of the pane

Front 63

Can you explain how the Tile Pane lays out its child nodes?

Back 63

A Tile Pane is similar to a Flow Pane

Nodes are in a grid, where each cell is the same size

Nodes can be laid out vertically or horizontally

Horizontal tiling wraps the tiles at the Tile Pane's width boundary, vertical at the height boundary

Front 64

Can you explain how a Tile Pane behaves when its container is resized?

Back 64

Gap properties can be set to manage the spacing between the rows and columns

The padding property can be set to manage the distance between the nodes and the edges of the pane

Front 65

Can you explain how an Anchor Pane lays out its child nodes?

Back 65

Anchor Panes enable you to anchor nodes to the top, bottom, left, right, or centre of the pane

Front 66

Can you explain how the Anchor Pane behaves when its container is resized?

Back 66

As the window is resized, the nodes maintain their position, relative to the anchor point

Nodes can be anchored to more than one position, and more than one node can be anchored to the same position

Front 67

What is the benefit of separating the controller in a typical MVC design?

Back 67

It allows for flexibility

Because the view doesn't care about the underlying model, supporting multiple file formats is easier - just add a model subclass for each

Front 68

What is an immutable object?

Back 68

An immutable object is one who's state cannot be changed

Front 69

Can you provide an example that shows how the String class is immutable?

Back 69

A string is initialised to a value, using the concat() method on that string returns a new string

The state of the original string is not changed as the value from concat() is not stored

Front 70

What is the difference between a String literal and a String object?

Back 70

A String literal is initialised like this:

String a = "abc";

If String b = "abc", a == b would return true

String c = new String("abc"); is a String object

String d = new String("abc");

c == d would return false because they have different references

Front 71

Can you explain how to make an immutable class?

Back 71

Declare the class as final, so it can't be extended

Make all fields private so that direct access is not allowed

Don't provide setter methods for variables

Make all mutable fields final so that its value can only be changed once

Initialise all fields via a constructor, performing deep copy

Perform cloning of objects in the getter methods to return a copy, rather than returning actual object reference

Front 72

Can you identify the requirement for, and implement, defensive copies?

Back 72

Any mutable objects within a field should be copied when being passed to a method