代写CSE 12 Winter 2024 Midterm Exam代做留学生Java程序
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Winter 2024
Midterm Exam
Concept 1 (6 pts). Java Generics
(Problem 1 - 5) Read the following generic class, Triplet, and answer the questions. The class has three generic variables, first, second, and third.
public class Triplet
1. Which of the following statement is true based on Line 1
A. Triplet is a child of Comparable
B. Generic type T must be a child of Comparable
C. Both A and B are correct
D. Neither A nor B is correct
private T first, second, third;
public Triplet(){
first = second = third = null;
}
public Triplet(T first, T second, T third){
this.first = first;//Line 2
2. True or False: If we remove this. in Line 2, the assignment won’t be correct.
A. True
B. False
this.second = second;
this.third = third;
}
public Triplet(Triplet p){
this.first = p.first;//Line 3
3. True or False: If we remove this. in Line 3, the assignment won’t be correct.
A. True
B. False
this.second = p.second;
this.third = p.third;
}
public int compareTo(Triplet other){
if(other.first.equals(first) && other.third.equals(third)){
return second.compareTo(other.second);
}
else{
return other.first.compareTo(first);
}
}
public static void main(String[] args){
//Line 4
}
}
4. Which of the following is the correct way to create a Triplet of Strings at the location of Line 4?
A. Triplet
B. Triplet
C. Triplet
D. All the approaches work.
E. None of the answers is correct.
5. Based on the definition of the CompareTo method from Java, please answer the question.
compareTo compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
Based on the compareTo method, which of the following Triplet
A. Triplet of (1, 3, 5)
B. Triplet of (2, 4, 4)
C. They are the same.
6. Which of the following is the correct way to create a generic array of type E with 10 elements? This problem isn't related to the problems above.
A. new E[10];
B. new Object[10];
C. (E[]) new Object[10];
D. More than once choices are correct
E. None of the answer is correct
Concept 2. (4 pts) JUnit and Testing
7. True or False: The @Test tag is used in JUnit to indicate the method is a tester method.
A. True B. False
(Problems 8 - 10). Suppose we need to write a tester for the following function dosth.
public class Foo{
String name;
public int dosth (){
//code to find a pattern in the name and returns the location of the first occurrence.
//this code may possibly throw a NullPointerException
} }
8. True or False: We need to change the signature of dosth to public boolean dosth (int a) throws NullPointerException to avoid a compiler error.
A. True B. False
9. True or False: In our tester, if we assume no exception is thrown, we only need to test if the dosth method returns the correct value. We shouldn’t test if this method changes name.
A. True B. False
10. True or False: If we use Junit test to test for exceptions, we can use try catch in our tester to test if the correct exception is thrown.
A. True B. False
Concept 3 (8 pts). ArrayList
(Problems 11 - 17). In our class and PA, we created our own generic ArrayList class. A part of the generic class is shown below (slightly modified from our PA2 code). Please answer the following questions
public class ArrayList < Problem 11 >{
Object[] arr; int size;
public ArrayList(E[] arr, int size){ this.arr = arr;
this.size = size; }
public E median (){
//Method to complete
}
//other methods
public static void main(String args[]){ Integer [] arr = new Integer[3];
arr[0] = 20; arr[1] = 10; arr[2] = 90;
ArrayList
System.out.println(arr[0]); //Problem 17 }
}
The median method will return the median of the array arr. It should throw a NullPointerException ifarr is null. It should throw an IllegalArgumentException if size is even. Please note that this method should not change arr. For example, ifarr is {1, 4, 2, 3, 1}, the median method should return 2. Ifarr is {“a”, “c”, “b”}, the method should return “b”. In other words, it should always return the element in the middle after sorting.
public E median(){
if( Problem 12 ){
throw new NullPointerException(); }
if( Problem 13 ){
throw new IllegalArgumentException(); }
Object[] tmp = Problem 14 ; for(int i = 0; i < size; ++i){
Problem 15 ;
}
Arrays.sort(tmp);
return (E) tmp[ Problem 16 ]; }
11. True or False. For the generic type for the ArrayList class, we should let it extend Comparable interface so we can guarantee the median method to work.
A. True B. False
12. Select the correct statement for problem 12
A. arr == null B. arr.length == 0 C. size == 0 D. More than one choice is correct. E. No
choice is correct
13. Select the correct statement for problem 13
A. size%2==0 B. arr.length%2 == 0 C. Both A and B are correct D. No choice is correct
14. Select the correct statement for problem 14. Select the best choice and pay attention to the for loop beneath problem 14 blank.
A. arr B. new Object[size] C. Both A and B are correct D. No choice is correct
15. Select the correct choice for problem 15
A. tmp[i] = arr[i] B. tmp[i] = this.arr[i] C. Both A and B are correct D. No choice is correct
16. Select the correct choice for problem 16
A. arr.length/2 B. size/2 C. Both A and B are correct D. No choice is correct
17. What will be printed out by the line for problem 17 in the main method? Assume we have implemented all methods correctly.
A. 20 B. 10 C. 90
18. If the arr in the ArrayList looks like the following and the array has a capacity of 5. If we call append(2). what will be the capacity of the array after expand capacity based on PA2?
|
9 |
12 |
3 |
7 |
8 |
A. 6 B. 7 C. 8 D. 10 E. 12
Concept 4 (9 pts). LinkedList
Problems 19-25. Look at the following Node class and answer questions. We assume that the constructors will properly connect a node with the node after it.
class Node
E data;
Node next; Node prev;
public Node(E data) { this.data = data;
next = null;
prev = null; }
public Node(E data, Node after) { this.data = data;
this.next = Problem 20 ;
this.prev = Problem 21 ;
if ( Problem 22 != null) {
after.prev.next = Problem 23 ; }
after.prev = Problem 24 ; }
}
public class Main {
public static void main(String[] args) {
Node
Node
} }
19. True or False: This linked list using this Node class should be a doubly linked list.
A. True B. False
20. What should be the correct statement for problem 20?
A. after.prev B. after C. after.next D. None is correct E. More than 1 is correct
21. What should be the correct statement for problem 21?
A. after.prev B. after C. after.next D. None is correct E. More than 1 is correct
22. What should be the correct statement for problem 22?
A. after.prev B. after C. after.next D. None is correct E. More than 1 is correct
23. What should be the correct statement for problem 23?
A. this B. this.next C. after.next D. after.prev E. None is correct
24. What should be the correct statement for problem 24?
A. this B. this.next C. after.next D. after.prev E. None is correct
25. Which of the following is "hello"?
A. n0.prev.data B.n2.next.data C. n2.prev.data D. More than 1 is correct.
E. None is correct
26. True or False: For our linked list assignment PA3, our contains method from the linked list class throws an exception if the starting location is negative.
A. True B. False
27. What are the instance variables of our MyLinkedList class for PA3? Select all that apply
A. int size B. Node head C. Node tail D. int capacity E. int index
Concept 5 (3 pts): Iterators in Linked List
Problems 28 - 30 are about the following iterator. None of the questions are sequential to each other.
28. True or False: Given the current state of the iterator, the mostrecent call to move the iterator must be it.next() instead of it.previous()
A. True B. False
29. True or False: Given the current state of the iterator, when we call it.previous() now, 10 will be returned.
A. True B. False
30. True or False: Given the current state of the iterator, if we call it.remove() the node with value 20 will be deleted.
A. True B. False
Concept 5 (7 pts): Runtime
31. Select the correct tight O notation for the f(n) = 2n + 5
A. O(1) B. O(n) C. O(n2) D. O(n3) E. None of the answer is correct
32. Select the correct tight O notation for the f(n) = 2n2 + 2n + 5
A. O(1) B. O(n) C. O(n2) D. O(n3) E. None of the answer is correct
33. True or false: Iff(n) and g(n) both∈ O(h(n)), then f(n)∈θ(g(n)). We are not judging based on the tight bound for this problem.
A. True B. False
34. What’s the runtime of the following code? We assume the tight bound here. for (int i = 0; i < n/2; i++){
arr[i] = 0; }
for (int i = n-1; i >=0; i--){
for (int j = i+1; j < n/2; j++){
arr[j]++; }
A. O(1) B. O(n) C. O(n2) D. O(n3) E. None of the answer is correct
(Problems 33 - 35). Given the following code and answer the questions. Assume that the size of the linkedlist is n.
//Block 1
LinkedList
ListIterator
System.out.println(it.next()); }
//Block 2
LinkedList
for (int i = 0; i
}
35. What is the runtime of block 1 code to traverse the list? We are looking for the tightest bound.
A. O(n) B. O(n2) C. O(nlogn) D. O(logn) E. None of the answers is correct
36. What is the runtime of block 2 code to traverse the list? We are looking for the tightest bound.
A. O(n) B. O(n2) C. O(nlogn) D. O(logn) E. None of the answers is correct
37. True or False. For blocks 2, there is no difference between the best case and worst case scenarios give the same list size n.
A. True B. False