[Solved] SOLVED:Exam 1 Review Problems

1. Suppose we have a class A which has a constructor that takes a single integer.(a) After the following statements have been executed, how many A objects will exist(not counting garbage objects) and which objects are they? Explain your answerand include in your explanation a picture of Javas memory.A a = new A(100);A b = new A(150);A c = b;b = a;a = null;(b) After the following statements have been executed, how many A objects will exist(not counting garbage objects) and which objects are they? Explain your answerand include in your explanation a picture of Javas memory.A a1 = new A(200);A a2 = new A(250);A a3 = a2;a2 = a1;a1 = null;2. Here is a simple Point and Circle class.class Point class Circle{ private double x, y; { private Point c; // centerprivate double r; // radiuspublic Point(double x, double y){ this.x = x; public Circle(Point c, double r)this.y = y; { this.r = r;} this.c = c;public double getX(){ return x; } }public double getY(){ return y; } // more stuff} }(a) The constructor in Circle has a privacy leak. Explain why.Hint: Consider the following code.Point p = new Point(1,2);Circle c = new Circle(p, 10);p.setX(100);(b) Rewrite the Circle constructor to fix this problem.3. Consider this code that creates some Location objects:Location a, b, c;a = new Location(10,20);b = new Location(10,20);c = b;After this code executes, what are the values of these boolean expressions?a==ba.equals(b)a==ca.equals(c)b==cb.equals(c)Also, write two clear sentences that explain the difference between == and the equals()method.4. Consider this code that creates some Location objects:Location a, b, c;a = new Location(10,20);b = (Location)a.clone( );c = a;c.shift(2,0);After this code executes, what are the values of these boolean expressions?a==ba.equals(b)a==ca.equals(c)b==cb.equals(c)5. What does the following program print out. Explain why.class Thing{ public int a;public int b;public Thing(int a, int b){this.a=a; this.b=b}}public class Test{ public static void f(Thing x, int y){x.a++;y++;}public static void main(String[] args){Thing x = new Thing(1,1);int y = 1;f(x, y);System.out.println(x.a = + x.a + and x.b = + x.b);System.out.println( y = + y);}}6. Suppose that we have classes A, B, C and D. Suppose that B is a subclass of A, that C is asubclass of B, and D is a subclass of A. Suppose that we make the following declarations.A a1 = new A();A a2 = new C();D d1 = new D();For each part below, explain what, if any, errors would be caused by the statement inthat part. Be sure to consider both compile time and run time errors.(a) A a3 = new B();(b) B b1 = new A();(c) B b2 = (B) a1;(d) B b3 = (B) a2;(e) B b4 = (B) d1;(f) B b5 = (C)(A)new D();7. Consider the following classes:public class Organization extends Object {Organization() { /* null constructor */ }public void printMe() { System.out.println(Organize.); }}public class Company extends Organization {Company() { /* null constructor */ }public void printMe() { System.out.println(Be productive.); }}public class MidCap extends Company {MidCap() { /* null constructor */ }public void printMe() { System.out.println(Think big.); }}public class InternetCo extends MidCap {InternetCo() { /* null constructor */ }public void printMe() { System.out.println(Be cool.); }public static void main(String[] args) {Company mid = new MidCap();MidCap netscape = new InternetCo();Object obj = new Organization();Organization startup = new Company();mid.printMe();netscape.printMe();((Organization) obj).printMe();obj = netscape;((MidCap) obj).printMe();obj = startup;((Organization) obj).printMe();}}What is the output from running the InternetCo class?8. Suppose we implement the IntArrayBag class using two partially-filled, parallel arraysinstead of a single (partially-filled) array. The first array, data, holds the values of theitems in the bag and the second array, dataCounts, holds a count of the number of timesthat the associated item is in the bag. In other words, data[i] is an integer in the bag,and dataCounts[i] is the number of times that integer is in the bag.We assume that there is an instance variable manyDataItems that tells us how many ofthe entries from the partially-filled arrays data and dataCounts are used to hold itemsfrom the bag (so manyDataItems <= data.length). The instance variable manyItemsis a count of how many items are in the bag.We assume that the part of the array data that stores the bag does not have any duplicateentries and we assume that each value in dataCounts is strictly greater than zero for allelements with index less than manyDataItems.(a) Describe what is meant by the capacity of a bag in this implementation.(b) Describe an advantage that this implementation of IntArrayBag has over the singlearray implementation from the textbook.(c) Describe a disadvantage that this implementation of IntArrayBag has when com-pared to the single array implementation from the textbook.(d) Write an implementation for each of the add(int element) and remove(int target)methods (see the next page).public class IntArrayBag{ // use two partially-filled parallel arraysprivate int[ ] data; // the data itemsprivate int[ ] dataCounts; // how many times each item is in the bagprivate int manyDataItems; // number of elements in partially-filled arrayprivate int manyItems; // total number of items in the bagpublic IntArrayBag( ){ final int INITIAL_CAPACITY = 10;data = new int[INITIAL_CAPACITY];dataCounts = new int[INITIAL_CAPACITY];manyDataItems = 0;manyItems = 0;}public IntArrayBag(int initialCapacity){ if (initialCapacity < 0) throw new IllegalArgumentException(Capacity<0.);data = new int[initialCapacity];dataCounts = new int[initialCapacity];manyDataItems = 0;manyItems = 0;}/** Add a new element to this bag. If the new element would take this* bag beyond its current capacity, then the capacity is increased. **/public void add(int element){}//add()/** Remove one copy of a specified element from this bag.* If target was found in the bag, then one copy of target* has been removed and the method returns true. Otherwise* the bag remains unchanged and the method returns false. **/public boolean remove(int target){}//remove()}//IntArrayBag9. Here is part of the definition for a LinkedList class.class LinkedList{private ListNode head;private int size;public LinkedList(){this.head = null;this.size = 0;}// a private classclass ListNode{public int item; // An item in the list.public ListNode next; // Reference to next item in the list.}// LinkedList methods}(a) Write a methodpublic void add( int element )that adds a new node at the head of the linked list. (Notice that the inner classListNode only has a default constructor.)(b) Write a methodpublic int remove( )that removes from the linked list the node at the head of the list and returns theint that was stored in that node. Throw an exception if the linked list is empty.(c) Explain how you would modify the add method so that the following two lines ofcode will compile.LinkedList list = new LinkedList();list.add(3).add(2).add(5).add(0).add(8);10. On the last page of these review problems is an implementation of the IntNode class.(a) Write an implementation of the static methodpublic static int countZeros( IntNode node )that will count the number of zeros that occur in the given linked list of ints.(b) Write an implementation of a static methodpublic static String list2String( IntNode node )that returns a String representation of the linked list referred to by the parameternode. If the linked list is empty, the String representation should be [] (twosquare brackets next to each other). If the linked list is not empty, the Stringrepresentation should look like this, [ 3 52 0 2 -4 16 ], with a space beforeeach entry of the list and a space before the closing bracket.(c) Write a methodpublic static IntNode removeFirst( IntNode head )that returns a reference to the second node from the linked list referred to by theparameter head.(d) Write a methodpublic static IntNode addFirst( int element, IntNode head )that returns a reference to the new head of a linked list with a node containingelement followed by the list referred to by the parameter head.(e) Write a methodpublic static void set( int element, int i )that modifies the list referred to by the parameter head so that the ith node inthe list has its data changed to element. If there is no ith node in the list, thenthe list is not modified.11. Once again using the IntNode class, consider the following three lines of code.IntNode head = new IntNode(4,new IntNode(7,new IntNode(5,new IntNode(3,null))));IntNode ptr = head.getLink().getLink();head.getLink().setLink( new IntNode(22, null) );(a) Draw a picture of Javas memory after the first line above has been executed. Besure to include what data is in each node.(b) Draw a picture of Javas memory after the first and second lines above have beenexecuted.(c) Draw a picture of Javas memory after all three lines above have been executed.(d) What would be a String representation for the linked list referred to by head?(e) What would be a String representation for the linked list referred to by ptr?(f) What would be a String representation for the linked list referred to by ptr afterexecuting the following line (which would be executed after the above three lines)?ptr.getLink().setLink( head.getLink() );12. (a) In the class name IntArrayBag, explain the significance of each part of the name:int, array, and bag.(b) In the class name IntArraySeq, explain the significance of each part of the name:int, array, and seq.(c) In the class name DoubleLinkedBag, explain the significance of each part of thename: double, linked, and bag.13. Suppose thatx = y;is a widening assignment.(a) If x and y are primitive variables, explain why the assignment can also be referredto as a widening conversion.(b) If x and y are reference variables, how are the types of x and y related to eachother?(c) If x and y are reference variables, explain why the assignment should not be referredto as a conversion.(d) If x and y are reference variables, you can even make a case that the assignmentshould be called a narrowing assignment. Explain why. (Hint: What can you sayabout the methods callable on x as compared to the methods callable on y?)14. Let A be an array of size n  2 containing integers from 1 to n1, inclusive, with exactlyone number repeated.(a) Write a methodpublic static int findRepeatedNumber(int[] A)that returns the value of the repeated number in the array A.(b) Rewrite the method so that it uses just a sinlge loop. (Hint: Make use of anotherarray.)15. Suppose that a Sequence ADT has the following interface.public interface Sequence{ public int size(); // Return number of elements in sequence.public void addFirst(int e); // Insert e at the front of the sequence.public void addLast(int e); // Insert e at the back of the sequence.// Inserts an element e to be at index i.public void add(int i, int e) throws IndexOutOfBoundsException;// Returns the element at index i, without removing it.public int get(int i) throws IndexOutOfBoundsException;// Removes and returns the element at index i.public int remove(int i) throws IndexOutOfBoundsException;}Starting with an empty sequence A, below each operation write down what the (cumula-tive) contents of the list would be after performing the operation. (Write the contents ofthe sequence as a horizontal, comma separated, list of numbers with the index 0 elementon the left.)A.add(0, 4)A.add(0, 3)A.addFirst(2)A.addLast(7)A.add(2, 1)A.add(1, 4)A.add(1, 5)A.add(3, 2)16. Below is an outline of a class that implements a linked list of integer nodes with twosentinel nodes (see pages 240241 of the textbook).(a) Draw a picture of the empty list created by the default constructor.(b) Write an implementation for the addFirst() method.(c) Write an implementation for the removeFirst() method that assumes the list isnot empty.public class IntLinkedList{ IntNode head;IntNode tail;int manyItems;public IntLinkedList() // Create an empty list,{ tail = new IntNode(0, null); // with two sentinel nodes.head = new IntNode(0, tail);manyItems = 0;}/** Add a new node to the beginning of the list. */public void addFirst(int n){}/** Remove the first node from a nonempty list and return its data. */public int removeFirst(){}}//IntLinkedListclass IntNode{private int data;private IntNode link;public IntNode(int data, IntNode link){this.data = data;this.link = link;}public int getData( ) { return data; }public IntNode getLink( ) { return link; }public void setData(int data) { this.data = data; }public void setLink(IntNode link) { this.link = link; }}//IntNode10-12-2015 at 01:22 h