Week 3 - Intermediate Java - Handling Problems, Exceptions and Errors, Collections

Question 1

Describe the difference between exceptions and errors in Java.

Answer 1

In the java compilation process, the compiler checks that any checked exceptions that could be thrown are handled. If this is not the case, the compiler cannot compile the code. This is an example of a compilation error - not an exception.

Exceptions are never thrown during the compilation process - they can only be thrown when the code is executing (running). Compilation errors generally occur due to improper syntax, like calling a method that doesn’t exist, forgetting a semicolon on a line, using the wrong data type, using a reserved keyword incorrectly, and as we’ve shown, not handling checked exceptions properly.

Question 2

Exceptions are never …..

Answer 2

thrown during the compilation process - they can only be thrown when the code is executing (running).

Question 3

Compilation errors generally occur due to….(4)

Answer 3

improper syntax,
like calling a method that doesn’t exist,
forgetting a semicolon on a line,
using the wrong data type, using a reserved keyword incorrectly,
and as we’ve shown, not handling checked exceptions properly.

Question 4

The exception class hierarchy starts with the….

Answer 4

Throwable class which inherits from Object.

Question 5

The Exception and Error classes both extend

Answer 5

Throwable class

Question 6

An Error represents something that…

Answer 6

went so horribly wrong with your application that you should not attempt to recover from

Question 7

When the source code fails before it finishes compiling, this is known as a…?

Answer 7

Compilation error

Question 8

What class is a general class which provides an abstraction for all exceptions?

Answer 8

Exception

Question 9

Exceptions that require mandatory handling are called

Answer 9

checked exceptions, The compiler will check that such exceptions are handled by the program.

Question 10

The _____ class represents all possible objects that can be thrown by a throw statement and caught by a catch clause in a try..catch statement.

Answer 10

Throwable

Question 11

Subclasses of the class Exception which are not subclasses of ______ are checked exceptions.

Answer 11

RuntimeException

Question 12

If an error is predictable but unpreventable and reasonable to recover from, a checked exception should be used

Answer 12

True

Question 13

Since Java has exception-handling capability, programmers do not need to write code to handle exceptions.

Answer 13

False

Question 14

Exception handling can be done in one of two ways:

Answer 14

The first way is to place the statement in a try statement that has a catch clause that handles the exception.

The second way is to declare that the subroutine can throw the exception. This is done by adding a “throws” clause to the subroutine heading, which alerts any callers to the possibility that the exception might be generated when the subroutine is executed. The caller will, in turn, be forced either to handle the exception in a try statement or to declare the exception in a throws clause in its own header.

Question 15

Exception-handling is mandatory for…

Answer 15

any exception class that is not a subclass of either Error or RuntimeException.

Question 16

When risky code is written that has the possibility of throwing an exception, it can be dealt with in one of two ways:

Answer 16

Handling means that the risky code is placed inside a try/catch block

Declaring means that the type of exception to be thrown is listed in the method signature with the throws keyword. This is also called “ducking” the exception - you let the code which calls the method deal with it.

Question 17

If the exception is not handled anywhere in the program, it will propagate up through the

Answer 17

call stack until it is handled by the JVM which then terminates the program.

Question 18

When an exceptional condition occurs in the course of a Java program, a special class called an Exception can be thrown,…

Answer 18

which indicates that something went wrong during the execution of the program.

Question 19

If an exception is NOT handled anywhere in the program, what will occur?

Answer 19

The exception propagates up through the call stack until it is handled by the JVM which will then terminate the program.

Question 20

Exception handling is done via…?

Answer 20

A try-catch block

Question 21

“Ducking” or declaring an exception is done with which keyword?

Answer 21

throws

Question 22

Code that executes at the end of a try-catch block is designated with which keyword?

Answer 22

finally

Question 23

When risky code is written that has the possibility of throwing an exception, it can be dealt with in one of two ways:

Answer 23

Handling means that the risky code is placed inside a try/catch block

Declaring means that the type of exception to be thrown is listed in the method signature with the throws keyword. This is also called “ducking” the exception - you let the code which calls the method deal with it.

Question 24

What is troubleshooting?

Answer 24

Troubleshooting is a process that helps people identify issues or problems occurring in a system.

Question 25

_____ is a troubleshooting technique where you get more info on the specifications, configuration setup, and events that occurred.

Answer 25

Drilling down

Question 26

Troubleshooting occurs at a lower level than debugging.

Answer 26

False

Question 27

Troubleshooting can be applied to any system.

Answer 27

True

Question 28

The Collections framework in Java is a

Answer 28

set of classes and interfaces that implement commonly used data structures. A collection is a single object which acts as a container for other objects.

Question 29

The important interfaces in the Collections API are:

Answer 29

Iterable - guarantees the collection can be iterated over
List - an ordered collection
Set - a collection does not contain duplicates
Queue - a collection that operates on a first-in-first-out (FIFO) basis
Map - contains key/value pairs. Does not extend Iterable.

Question 30

Iterable

Answer 30

guarantees the collection can be iterated over

Question 31

List

Answer 31

List - an ordered collection
This interface represents a collection of elements whose elements are arranged sequentially ordered.
List maintains an order of elements means the order is retained in which we add elements, and the same sequence we will get while retrieving elements.
We can insert elements into the list at any location. The list allows storing duplicate elements in Java.
ArrayList, vector, and LinkedList are three concrete subclasses that implement the list interface.

Question 32

Set - a collection does not contain duplicates

Answer 32

Set - a collection does not contain duplicates
This interface represents a collection of elements that contains unique elements. i.e, It is used to store the collection of unique elements.
Set interface does not maintain any order while storing elements and while retrieving, we may not get the same order as we put elements. All the elements in a set can be in any order.
Set does not allow any duplicate elements.
HashSet, LinkedHashSet, TreeSet classes implements the set interface and sorted interface extends a set interface.
It can be iterated by using Iterator but cannot be iterated using ListIterator.

Question 33

Queue

Answer 33

Queue - a collection that operates on a first-in-first-out (FIFO) basis
A queue is an ordered of the homogeneous group of elements in which new elements are added at one end(rear) and elements are removed from the other end(front). Just like a queue in a supermarket or any shop.
This interface represents a special type of list whose elements are removed only from the head.
LinkedList, Priority queue, ArrayQueue, Priority Blocking Queue, and Linked Blocking Queue are the concrete subclasses that implement the queue interface.

Question 34

Map

Answer 34

Map - contains key/value pairs. Does not extend Iterable.

Question 35

SortedSet Interface

Answer 35

This interface extends a set whose iterator transverse its elements according to their natural ordering.
TreeSet implements the sorted interface.

Question 36

Deque Interface

Answer 36

A deque (double-ended queue) is a sub-interface of queue interface.
This interface was added to the collection framework in Java SE 6.
Deque interface extends the queue interface and uses its method to implement deque. The hierarchy of the deque interface is shown in the below figure.
Deque hierarchy in JavaIt is a linear collection of elements in which elements can be inserted and removed from either end. i.e, it supports insertion and removal at both ends of an object of a class that implements it.
LinkedList and ArrayDeque classes implement the Deque interface.

Question 37

Map Interface

Answer 37

Map interface is not inherited by the collection interface. It represents an object that stores and retrieves elements in the form of a Key/Value pairs and their location within the Map are determined by a Key.
The hierarchy of the map interface is shown in the below figure.Map hierarchy in Java
Map uses a hashing technique for storing key-value pairs.
It doesn’t allow to store the duplicate keys but duplicate values are allowed.
HashMap, HashTable, LinkedHashMap, TreeMap classes implements Map interface.

Question 38

SortedMap Interface

Answer 38

This interface represents a Map whose elements are stored in their natural ordering. It extends the Map interface which in turn is implemented by TreeMap classes.

Question 39

A List is a collection that is

Answer 39

ordered and preserves the order in which elements are inserted into the list. Contrary to sets, duplicate entries are allowed. Also, elements are accessed by their index, which begins with 0 for the first element in the list.

Question 40

An ArrayList is a concrete class which implements

Answer 40

List. It is a data structure which contains an array within it, but can resize dynamically.

Question 41

A LinkedList implements both the

Answer 41

List and Queue interfaces, so it has all methods in both interfaces. The data structure is composed of nodes internally, each with a reference to the previous node and the next node - i.e. a doubly-linked list.

Question 42

Which of these is NOT a characteristic of the List interface?

It does not preserve the order in which elements are inserted.
Duplicate entries are allowed.
Elements are accessed by index
List inherits operations from Collections as well as adding some of its own.

Answer 42

It does not preserve the order in which elements are inserted.

Question 43

Which of these is not an additional operation provided by the List interface?

eliminate()
get()
set()
addAll()

Answer 43

eliminate()

Question 44

Which of these is not an additional operation provided by the List interface?

Answer 44

firstIndexOf()

Question 45

A ______ comprises a sequence of nodes with each node containing a reference to its successor and can be used to implement Stacks and Queues.

Answer 45

LinkedList

Question 46

A ______ is more efficient for random access and less efficient for inserting/removing elements when compared to ______

Answer 46

ArrayList, LinkedList

Question 47

Select the incorrect choice regarding LinkedList.

LinkedList is index driven.
LinkedList is faster at middle of the list retrieval/addition.
LinkedList implements List.
LinkedList implements Deque.

Answer 47

LinkedList is index driven.

Question 48

______ is a List implementation that also implements the Queue and Deque interfaces.

Answer 48

LinkedList

Question 49

Wrapper classes are

Answer 49

classes that let you treat primitives as Objects.

Question 50

Boxing is the….

Answer 50

process of converting a primitive to its wrapper class
Java has a feature called autoboxing which will automatically convert primitives to wrapper classes implicitly.

Question 51

Unboxing is the…

Answer 51

reverse - converting a wrapper class to its primitive.

Question 52

Wrapper classes have static helper methods like

Answer 52

.parseX() and .valueOf() for explicit primitive conversion.

Question 53

What is the correct name for the wrapper class for the int type?

Answer 53

Integer

Question 54

What is the process of converting a primitive to its wrapper class?

Answer 54

Boxing

Question 55

What is the process of converting a wrapper class to its primitive?

Answer 55

Unboxing

Question 56

What is the Java process that implicitly converts a primitive to its wrapper class?

Answer 56

Autoboxing

Question 57

The Queue places objects on a “waiting list”, typically based on

Answer 57

First-In-First-Out (FIFO)

Question 58

What is a queue data structure useful for?

Answer 58

Useful for storing objects prior to processing
Elements are added to the tail of the queue
Elements can be “popped” off the frot of the queue

Question 59

The Deque Interface extends the…

Answer 59

Queue interface

Question 60

Deque is useful for…

Answer 60

Short for “double-ended queue”
Pronounced “deck”
Supports element insertion and removal from both ends of the queue
Can be used to implement a stack, with Last-In-First-Out (LIFO) behavior

Question 61

Queue implementations include: (4)

Answer 61

LinkedList
ArrayDeque
PriorityQueue
ArrayBlockingQueue

Question 62

A ______ supports the insert and remove operations using a first-in first-out (FIFO) order.

Answer 62

Queue

Question 63

______ is a resizable array implementation of Deque that is likely to be faster than Stack when used as a stack, and faster than LinkedList when used as a queue.

Answer 63

ArrayDeque

Question 64

______ is an array-backed collection that acts as a “bounded buffer”, in which a fixed-sized array holds elements inserted by producer threads and extracted by consumer threads. Attempts to put an element into a full queue will result in the operation blocking; attempts to take an element from an empty queue will similarly block.

Answer 64

ArrayBlockingQueue

Question 65

______ is a List implementation that also implements the Queue and Deque interfaces

Answer 65

LinkedList

Question 66

Description of the Set Interface data structure?

Answer 66

The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.

Set also adds a stronger contract on the behavior of the equals and hashCode operations, allowing Set instances to be compared meaningfully even if their implementation types differ.

Question 67

A HashSet implements Set and is backed by a HashMap. It:

Answer 67

Guarantees no ordering when iterating
Allows one null value
Allows fast insertion and traversal
Does not maintain order in which you insert elements

Question 68

What is a TreeSet?

Answer 68

A TreeSet is a Set whose elements maintain sorted order when inserted. Internally, it is backed by a Sorted Tree. Insertion and removal of elements is slow, because the elements must maintain sorted order. It cannot contain any null values, since null cannot be compared to any object.

Question 69

Which of the following is NOT a method provided by the Set Interface?
delete()
contains()
isEmpty()
iterator()

Answer 69

delete()

Question 70

Which of the following is the main distinction with the Set interface?

Answer 70

Duplicate elements are not allowed in a Set

Question 71

Which of the following is NOT an implementation of the Set interface?

Answer 71

StackSet

Question 72

Which of the following is NOT a method provided by the Set Interface?
length()
add()
remove()
size()

Answer 72

length()

Question 73

HashMap is a Map which:

Answer 73

Stores elements in key-value pairs
Insertion/Retrieval of element by key is fast
Tradeoff is that it does not maintain the order of insertion
Permits one null key and null values

Question 74

HashMap is a Map which:

Answer 74

Stores elements in key-value pairs
Insertion/Retrieval of element by key is fast
Tradeoff is that it does not maintain the order of insertion
Permits one null key and null values

Question 75

TreeMap is a Map whose:

Answer 75

Keys are stored in a Sorted Tree structure
Main benefit is that keys are always in a sorted order
Insertion/Retrieval are slow
Cannot contain null keys as null cannot be compared for sorting

Question 76

HashTable is an older, thread-safe implementation of a

Answer 76

HashMap. It does not allow null keys or null values

Question 77

A Map is useful if you have to

Answer 77

search, update or delete elements on the basis of a key.

Question 78

Map implements the Collection interface.

Answer 78

False

Question 79

The Map interface defines an iterator() method.

Answer 79

False

Question 80

Syntax for hashmap

Answer 80

Map<Integer,String> map=new HashMap<Integer,String>();

Question 81

Define the access modifiers in Java

Answer 81

Access modifiers are simply keywords in Java that provides accessibility of a class and its member. They set the access level to methods, variable, classes and constructors.
public, protected default, private

Question 82

There are 4 types of access modifiers available in Java

Answer 82

public
default
protected
private

Question 83

Define public access modifiers

Answer 83

The member with public modifiers can be accessed by any classes. The public methods, variables or class have the widest scope.

Question 84

Define default access modifiers

Answer 84

default: When we do not mention any access modifier, it is treated as default. It is accessible only within same package

Question 85

Define protected access modifiers

Answer 85

protected: The protected modifier is used within same package. It lies between public and default access modifier. It can be accessed outside the package but through inheritance only

Question 86

Define private access modifiers

Answer 86

private: The private methods, variables and constructor are not accessible to any other class. It is the most restrictive access modifier. A class except a nested class cannot be private.

Question 87

____ modifier allows access by any class.

Answer 87

public

Question 88

____ modifier allows access outside the package but through inheritance only.

Answer 88

protected

Question 89

____ is the most restrictive access modifier.

Answer 89

private

Question 90

Java provides a number of non-access modifiers to achieve many other functionalities. (3)

Answer 90

The static modifier for creating class methods and variables.
The final modifier for finalizing the implementations of classes, methods, and variables.
The abstract modifier for creating abstract classes and methods.

Question 91

Java provides a number of non-access modifiers to achieve many other functionalities. (3)

Answer 91

The static modifier for creating class methods and variables.
The final modifier for finalizing the implementations of classes, methods, and variables.
The abstract modifier for creating abstract classes and methods.

Question 92

Static Variables:

Answer 92

The static keyword is used to create variables that will exist independently of any instances created for the class. Only one copy of the static variable exists regardless of the number of instances of the class.
Static variables are also known as class variables. Local variables cannot be declared static.

Question 93

Static Methods

Answer 93

The static keyword is used to create methods that will exist independently of any instances created for the class.

Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables.

Class variables and methods can be accessed using the class name followed by a dot and the name of the variable or method.

Question 94

Final Variables

Answer 94

A final variable can be explicitly initialized only once. A reference variable declared final can never be reassigned to refer to a different object.

However, the data within the object can be changed. So, the state of the object can be changed but not the reference.

With variables, the final modifier often is used with static to make the constant a class variable.

Question 95

Final Methods

Answer 95

A final method cannot be overridden by any subclasses. As mentioned previously, the final modifier prevents a method from being modified in a subclass.

The main intention of making a method final would be that the content of the method should not be changed by any outsider.

Question 96

Final Classes

Answer 96

The main purpose of using a class being declared as final is to prevent the class from being subclassed.

If a class is marked as final then no class can inherit any feature from the final class.

Question 97

Abstract Methods

Answer 97

An abstract method is a method declared without any implementation. The methods body (implementation) is provided by the subclass. Abstract methods can never be final or strict.

Any class that extends an abstract class must implement all the abstract methods of the super class, unless the subclass is also an abstract class.
If a class contains one or more abstract methods, then the class must be declared abstract. An abstract class does not need to contain abstract methods.

The abstract method ends with a semicolon. Example: public abstract sample();

Question 98

Abstract Class

Answer 98

An abstract class can never be instantiated. If a class is declared as abstract then the sole purpose is for the class to be extended

A class cannot be both abstract and final (since a final class cannot be extended). If a class contains abstract methods then the class should be declared abstract. Otherwise, a compile error will be thrown.

An abstract class may contain both abstract methods as well normal methods.

Question 99

The _____ keyword is used to create variables that will exist independently of any instances created for the class

Answer 99

static

explanation: In object-oriented programming, the static keyword is used to define a variable or a method that is associated with the class itself, rather than with any specific instance of the class. This means that the variable or method can be accessed using the class name, rather than an object reference.

For example, let’s say you have a class called Car. You might define a static variable called numCars to keep track of the total number of cars created, like this:

class Car {
static int numCars = 0;
// Other class members here…
}

In this case, the numCars variable belongs to the Car class as a whole, rather than to any particular instance of Car. It’s declared as static, which means that it’s not tied to any specific object, and can be accessed using the class name (Car.numCars) rather than an instance (myCar.numCars).

Static variables are useful when you want to keep track of some information that’s related to the class as a whole, rather than to any specific instance. They’re also used to create constants, which are variables that can’t be changed after they’re initialized.

Static methods work in a similar way. They belong to the class as a whole, rather than to any specific instance, and can be accessed using the class name. They’re often used for utility functions that don’t require any state information from an instance of the class.

Question 100

A class can be both abstract and final.

Answer 100

False

Question 101

How often can a final variable be initialized?

Answer 101

Only once

Question 102

An abstract class can have both abstract methods and non-abstract methods. T/F?

Answer 102

True

Question 102

An abstract class can have both abstract methods and non-abstract methods. T/F?

Answer 102

True

Question 103

What is a static member in Java?

Answer 103

A static member in Java is a member of a class that is not associated with an instance of a class, but rather belongs to the class itself.

Question 104

How is the static keyword used in Java?

Answer 104

The static keyword in Java is mainly used for memory management and is used to share the same variable or method of a given class. It can be applied to variables, methods, blocks, and nested classes.

Question 105

What can the static keyword be applied to in Java?

Answer 105

The static keyword can be applied to blocks, variables, methods, and classes.

Question 106

What is a non-access modifier in Java?

Answer 106

A non-access modifier in Java is a keyword that is used to modify the default behavior of a class or its members. The static keyword is a non-access modifier in Java.

Question 107

What is the purpose of the static keyword in Java?

Answer 107

The purpose of the static keyword in Java is mainly for memory management and sharing the same variable or method of a given class.

Question 108

What is a constant variable in Java?

Answer 108

A constant variable in Java is a variable that cannot be changed after it is initialized.

Question 109

What type of methods are often declared as static methods?

Answer 109

Utility functions that don’t require any state information from an instance of the class are often declared as static methods.

Question 110

How can you access a static member in Java?

Answer 110

You can access a static member in Java using the class name, rather than an object reference.

Question 111

The static keyword is a non-access modifier in Java that is applicable for the following:

Answer 111

Blocks
Variables
Methods
Classes

Question 112

When a member is declared static, it can be accessed before any

Answer 112

objects of its class are created, and without reference to any object.

Question 113

A _________ is a member of a class that is not associated with an instance of a class.

Answer 113

static member

Question 114

Static variables can be created at the class level only

Answer 114

True

Question 115

Define the term variable scope.

Answer 115

When a variable is declared in a Java program, it is attached to a specific scope within the program, which determines where the variable resides.

Question 116

The different scopes of a variable in Java are:

Answer 116

Instance, or object, scope
Class, or static, scope
Method scope
Block scope

Question 117

Instance scope means that the variable is

Answer 117

attached to individual objects created from the class. When an instance-scoped variable is modified, it has no effect on other, distinct objects of the same class.

Question 118

Class, or static, scope

Answer 118

Resides on the class definition itself.

Question 119

Method scope

Answer 119

Declared within a method block; only available within the method in which they are declared.

Question 120

Block scope

Answer 120

Only exist within the specific control flow block (for, while, etc.)

Question 121

When a variable is attached to individual objects created from the class, it has what type of scope?

Answer 121

Instance, or object, scope

Question 122

When a variable resides in the class definition itself, it has what type of scope?

Answer 122

Class, or static, scope

Question 123

When the scope of a variable declared within a method block, it has what type of scope?

Answer 123

Method scope

Question 124

When a variable only exists within the specific control flow block, it has what type of scope?

Answer 124

Block scope