# Exam 2

```Solutions to example exam 2
1
1. Describe how to scan a two-dimensional array. Describe
the pseudocode and explain as clearly as possible how it
works.
Solution:
See assignment 3.
- describe the main idea, which data it can be used on.
- Write the pseudo code
- Give example of how it works.
2
2. Write the code for two classes that inherit from the class
(SuperClass2) below and contains at least one self
method.
public class SuperClass2 {
int number = 2;
public int getNumber {
return number;
}
}
3
Question 2 – Solution
public class SubClass1 extends SuperClass2 {
// constructor
public SubClass1() {}
// method
public void print(){
System.out.println("SubClass1");
}
}
4
Question 2 – Solution
public class SubClass2 extends SuperClass2 {
// constructor
public SubClass2() {}
// method
public void print(){
System.out.println("SubClass2" + number);
}
}
5
3.Explain the FIFO-structure and the most common methods
we can use on the structure. Give an example.
Solution:
FIFO stands for First In First Out- structure. FIFO means that
the data that was added first in the in structure is removed first.
Operations:
enqueue(data) – adds the data last in the structure
Dequeue() - removes the first data in the structure
and returns it.
peek() - returns the first element in the structure
without removing it from the structure
isEmpty() - returns true if the structure is empty and false otherwise.
6
3.Explain the FIFO-structure and the most common methods
we can use on the structure. Give an example.
Example: The number 1 is placed last in the
FIFO-structure
2 3
enqueue(1)
2 3 1
7
3.Explain the FIFO-structure and the most common methods
we can use on the structure. Give an example.
Example: The number 2 is removed from the
FIFO-structure
2 3 1
dequeue()
3 1
8
3.Explain the FIFO-structure and the most common methods
we can use on the structure. Give an example.
Example: Look at the first element in the FIFO-structure
and return it
2 3 1
peek()
2
9
3.Explain the FIFO-structure and the most common methods
we can use on the structure. Give an example.
Example: Test if the FIFO-structure is empty.
2 3 1
isEmpty()
false
10
4. What will the program below print out? Explain example 5
and 10 in detail.
public class TestRegularExpression {
private static void tryReg(String
String
{
if (text.matches(regexp)) {
System.out.println(ex + "
} else {
System.out.println(ex + "
}
}
ex, String regexp,
text)
matchar.");
matchar INTE.");
11
Question 4
public static void main(String[] args) {
tryReg("Exempel 1" , "a?b.*", "bbc");
tryReg("Exempel 2" , "(ac)+b", "acacb");
tryReg("Exempel 3" , "ab*c?", "a");
tryReg("Exempel 4" , "ab*c?", "ac");
tryReg("Exempel 5" , "cb*a", "cba");
tryReg("Exempel 6" , "(ba)?b*", "babbbbbb");
tryReg("Exempel 7" , "(ba)?b*", "");
tryReg("Exempel 9" , "((aca)|(bb)).*c.*d?", "bbd");
tryReg("Exempel 10" , "((aca)|(bb)).*c.*d?",
"bbacabbccd");
}
}
12
Question 4 – Solution
tryReg("Exempel 1" , "a?b.*", "bbc");
Printout:
Exempel 1 matchar.
Explanation:
a?
b
.*
- option, a either exists or not
- b must exist
- something may exist
13
Question 4 – Solution
tryReg("Exempel 2" , "(ac)+b", "acacb");
Printout:
Exempel 2 matchar.
Explanation:
(ac)+
b
- ac must exist 1 or more times
- the string must end with b
14
Question 4 – Solution
tryReg("Exempel 3" , "ab*c?", "a");
tryReg("Exempel 4" , "ab*c?", "ac");
Printout:
Exempel 3 matchar.
Exempel 4 matchar.
Explanation:
a b* c? -
the string must begin with a
it must exist 0 or more b
option, the string may end with c
15
Question 4 – Solution
tryReg("Exempel 5" , "cb*a", "cba");
Printout:
Exempel 5 matchar.
Explanation:
c b* a -
the string must begin with c
it must exist 0 or more b
the string must end with a
“cba” starts with c, contains one b and ends with one a
→ the string matches the regular expression “cb*a”
16
Question 4 – Solution
tryReg("Exempel 6" , "(ba)?b*", "babbbbbb");
tryReg("Exempel 7" , "(ba)?b*", "");
Printout:
Exempel 6 matchar.
Exempel 7 matchar.
Explanation:
(ba)?
b*
-
option, the string may begin with ba
the rest of the string must consist of 0 or more b
17
Question 4 – Solution
tryReg("Exempel 9" , "((aca)|(bb)).c*.*d?", "bbd");
tryReg("Exempel 10" , "((aca)|(bb)).c*.*d?",
"bbacabbccd");
Printout:
Exempel 8 matchar INTE.
Exempel 9 matchar INTE.
Exempel 10 matchar.
Explanation:
((aca) | (bb))
.
c*
.*
d?
- the string must begin with aca or bb
- the string contains a symbol
- the string contains 0 or more c
- the string contain may contain something
- option, the string may end with d
18
Question 4 – Solution
tryReg("Exempel 10" , "((aca)|(bb)).c*.*d?",
"bbacabbccd");
Explanation:
((aca) | (bb))
.
c*
.*
d?
-
the string must begin with aca or bb
the string contain a symbol
the string contains 0 or more c
the string contain may contain something
option, the string may end with d
The string that matches the regular expression can be split
like this:
bb-a-c-abbcc-d
bb
– is fullfilled by ((aca) | (bb))
a
– is fullfilled by .
c
– is fullfilled by c*
abbcc – is fullfilled by .*
19
d
– is fullfilled by d?
5a. What strings with a length less than 4 match this
regular expression: "(ab?)*c*".
5b. Which strings with length less than 4 match this
regular expression: "(abc?|ac)*"
5c. Which strings with length less than 4 match this
20
5a. What strings with a length less than 4 match this
regular expression: "(ab?)*c*".
Solution:
Length 0: “”
Length 1: a, c
Length 2: aa, ab, ac, cc
Length 3: aaa, aab, aba, abc, aac, acc, ccc
21
5b. Which strings with length less than 4 match this
regular expression: "(abc?|ac)*"
Solution:
Length 0: “”
Length 1: does not exist
Length 2: ab, ac
Length 3: abc
22
5c. Which strings with length less than 4 match this
Solution:
Length 0: “”
Length 1: a, b
Length 2: aa, ab, ad, ba, bb
bbb, bba, bab, abb, bba, baa, bad
23
6. What do package, public, protected, and
private mean? Which visibility has them? Give
examples of how they should be used.
24
Question 6 - Solution
Solution:
package:
- The class and its methods and instance variables
are only visible to the classes in the same package
- Can be used to collect classes which have a common
Example:
The classes Cat and Dog are about animals
and can be placed in the package animal
if we write this in the beginning of the file:
package animal;
25
Question 6 - Solution
Solution:
Before a class outside the package can gain access
to classes in the package, the class must be
import the package:
import animal.*;
26
Question 6 - Solution
Solution:
protected
The method or the instance variable is available to
the suclasses in the same and other packages.
protected
Should only be used on the methods and instance
variables which the classes in the same package
and subclasses should have in common.
27
Question 6 - Solution
Example:
In the package school we have the class Person which
contains an instance variable declared with protected.
public class Person {
protected name = "Kalle";
}
28
Question 6 - Solution
Example:
In the package school we have the class Person which
contains an instance variable declared with protected.
public class Person {
protected name = "Kalle";
}
All classes in the package school and the classes that
inherit Person can use name directly without calling
getter/setter.
29
Question 6 - Solution
Solution:
private is used on classes, methods and
instance variables that should only be visible
to the class itself.
30
Question 6 - Solution
Example:
Only the class itself should know that the stack is based on
a linked list. All other classes should only have to consider
how they are going to use the class Stack.
public class Stack {
private class Node
{
int data;
Node next;
Node(E v, Node n) {
data = v;
next = n;
}
}
}
31
Question 6 - Solution
Visibility among members
public protected package private
Same class
YES
YES
YES
YES
Class in the same package
YES
YES
YES
NO
Subclass in a different
package
YES
YES
NO
NO
Not subclass, different
package
YES
NO
NO
NO
32
7. Write the code for a class that implements the
interface(Interface7). The method reverse(int []
array) reverses the array array.
}
public interface Interface7 {
public void reverse(int[] array);
33
Question 7 – Solution
public class Uppgift7 implements Inteface7 {
// Constructor
// Implement the method
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
34
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
4
3
1
35
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
i
4
3
1
36
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
4
i
4
3
1
37
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
1
i
4
3
1
Array.length – 1- i
38
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
1
i
4
3
4
Array.length – 1- i
39
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
4
i
3
4
40
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
1
4
i
3
4
41
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
1
3
i
3
4
Array.length – 1- i
42
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
swap: 4
1
3
i
4
4
Array.length – 1- i
43
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
3
4
i
4
44
Question 7 – Solution – Execution1
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
3
4
4
45
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
3
4
5
4
46
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
i
3
4
5
4
47
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
1
i
3
4
5
4
Array.length – 1- i
48
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
3
i
4
5
1
49
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
3
i
4
5
1
Array.length – 1- i
50
Question 7 – Solution – Execution2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
5
4
i
3
1
51
Assignment 7 – Solution – Execution 2
public class Uppgift7 implements Inteface7 {
public void reverse(int[] array) {
for(int i = 0; i < array.length / 2; i++){
int swap = array[i];
array[i] = array[array.length -1 – i];
array[array.length -1 – i] = swap;
}
}
}
array:
4
5
4
3
1
52
8. Write the code for the methodpublic boolean
isSorted() which returns true if the valuesin a
Stack<E> are in an ascending order. The method
should also be able to handle the same value in
different positions.
53
public class Stack<E extends Comparable<E>> {
private class Node
{
E data;
Node next;
Node(E v, Node n)
{
data = v;
next = n;
}
}
private Node top;
54
public void push(E v)
{
Node newTop = new Node(v,top);
top = newTop;
}
public E pop()
{
E v = top.data;
top = top.next;
return v;
}
}
55
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
}
return true;
}
}
56
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
3
data
next
2
57
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
3
data
next
2
58
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
3
data
next
2
59
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
data
return true;
top
}
currentNode:
3
next
data
next
2
60
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
61
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
62
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
63
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
64
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
65
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
66
Question 8 – Solution – Execution1
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
3
data
next
2
67
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
2
data
next
3
68
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
2
data
next
3
69
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
top
data
next
2
data
next
3
70
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
71
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
72
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
73
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
74
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
75
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
76
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
77
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
78
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
79
Question 8 – Solution – Execution2
public boolean isSorted() {
if(top == null)
return true;
else {
Node currentNode = top;
while(currentNode.next != null) {
if(currentNode.data.compareTo(
currentNode.next.data) > 0)
return false;
currentNode = currentNode.next;
}
return true;
}
currentNode:
top
data
next
2
data
next
3
80
```
Arab people

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