CSCI Problem Solving, Programming and Computers Spring, 2016 Assignment 2 {Inheritance, Interfaces, Arrays}

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1 CSCI Problem Solving, Programming and Computers Spring, 2016 Assignment 2 Inheritance, Interfaces, Arrays Q1. [20 points] Q1. TXT Short answer questions Fill in the blanks in each of the following statements: 1. If a class contains at least one abstract method, it s a(n) class.answer: abstract 2. Classes from which objects can be instantiated are called classes.answer: concrete 3. involves using a superclass variable to invoke methods on superclass and subclass objects, enabling you to program in the general. Answer: Polymorphism 4. Methods that are not interface methods and that do not provide implementations must be declared using keyword. Answer: abstract 5. An array that uses two indices is referred to as a(n) array. Answer: 2-D or 2-dimensional State whether each of the statements that follows is true or false. If false, explain why. 6. [TRUE / FALSE] All methods in an abstract class must be declared as abstract methods. Why? Answer: False. An abstract class can include methods with implementations and abstract methods 7. [TRUE / FALSE] Invoking a subclass-only method through a subclass variable is not allowed. Why? Answer: False. Trying to invoke a subclass-only method with a superclass variable is not allowed. 8. [TRUE / FALSE] If a superclass declares an abstract method, a subclass must implement that method. Why? Answer: False. Only a concrete subclass must implement the method 9. [TRUE / FALSE] An object of a class that implements an interface may be thought of as an object of that interface type. Why? Answer: True 10. [TRUE / FALSE] An individual array element that s passed to a method and modified in that method will contain the modified value when the called method completes execution. Why? Answer: For individual primitive-type elements of an array: False. A called method receives and manipulates a copy of the value of such an element, so modifications do not affect the original value. If the reference of an array is passed to a method, however, modifications to the array elements made in the called method are indeed reflected in the original. For individual elements of a reference type: True. A called method receives a copy of the reference of such an element, and changes to the referenced object will be reflected in the original array element.

2 Q2. [30 points] FindDistance.java Write a program FindDistance to display the distance between two cities. Sample program run is shown (user input bolded): >This program finds the distance between two cities. Supported cities: Atlanta, Boston, Chicago, Houston, Los Angeles, New York, San Francisco, Washington. Enter starting city: San Francisco Enter destination city: Atlanta The distance from San Francisco to Atlanta is 2480 miles. The user will be asked to re-enter the name of a city if it doesn t match any of the names supported by the program. A normal two-dimensional array will be used to store the distances between cities. A ragged array could be used instead. The city names are maintained in array CITY_NAMES. The distance between each two cities are maintained in array DISTANCE. For example distance between Atlanta and Boston is Note that index of Atlanta is 0 and Boston is 1 in CITY_NAMES. So DISTNCE[0][1] is the distance between two cities. Use following class template: public class FindDistance private static final String[] CITY_NAMES = "Atlanta", "Boston", "Chicago", "Houston", "Los Angeles", "New York", "San Francisco", "Washington"; private static final int[][] DISTANCES = 0, 1110, 710, 790, 2190, 850, 2480, 620, 1110, 0, 1000, 1830, 3020, 210, 3130, 450, 710, 1000, 0, 1090, 2050, 810, 2170, 710, 790, 1830, 1090, 0, 1540, 1610, 1910, 1370, 2190, 3020, 2050, 1540, 0, 2790, 390, 2650, 850, 210, 810, 1610, 2790, 0, 2930, 240, 2480, 3130, 2170, 1910, 390, 2930, 0, 2840, 620, 450, 710, 1370, 2650, 240, 2840, 0; public static void main(string[] args) //TODO: Display initial message, including a list of legal cities // TODO:Call getcitycode to obtain codes for starting city and destination city //TODO: Display distance between chosen cities private static int getcitycode(string prompt) // TODO: method getcitycode:prompts user to enter city name; returns corresponding city code(index of city in CITY_NAMES). If city name is not recognized, allows user to enter another name.

3 Answer: // Finds the distance between two major American cities import java.util.scanner; public class FindDistance private static final String[] CITY_NAMES = "Atlanta", "Boston", "Chicago", "Houston", "Los Angeles", "New York", "San Francisco", "Washington"; private static final int[][] DISTANCES = 0, 1110, 710, 790, 2190, 850, 2480, 620, 1110, 0, 1000, 1830, 3020, 210, 3130, 450, 710, 1000, 0, 1090, 2050, 810, 2170, 710, 790, 1830, 1090, 0, 1540, 1610, 1910, 1370, 2190, 3020, 2050, 1540, 0, 2790, 390, 2650, 850, 210, 810, 1610, 2790, 0, 2930, 240, 2480, 3130, 2170, 1910, 390, 2930, 0, 2840, 620, 450, 710, 1370, 2650, 240, 2840, 0; public static void main(string[] args) //10 points // Display initial message, including a list of legal // cities System.out.println( "This program finds the distance between two cities.\n" + "Supported cities: Atlanta, Boston, Chicago, Houston,\n" + "Los Angeles, New York, San Francisco, Washington.\n"); // Call getcitycode to obtain codes for starting city and destination city int start = getcitycode("enter starting city: "); int destination = getcitycode("enter destination city: "); // Display distance between chosen cities System.out.println("\nThe distance from " + CITY_NAMES[start] + " to " + CITY_NAMES[destination] + " is " + DISTANCES[start][destination] + " miles."); // Prompts user to enter city name; returns corresponding city code. If city name is not recognized, allows user to enter another name. private static int getcitycode(string prompt) //15 points Scanner sc = new Scanner(System.in); while (true) System.out.println(prompt); String cityname = sc.nextline().trim(); for (int i = 0; i < CITY_NAMES.length; i++) if (cityname.equalsignorecase(city_names[i])) return i; System.out.println("City name was not recognized."); //5 points -comments

4 Q3. [20 points] StringReverse.java Write a program StringReverse with following methods to reverse a string:. For example, reverse("hello!") returns the string "!olleh. 1. a recursive method reverse(string text) that reverses a string 2. A iterative method reverse2(string text) that reverses a string Use following class template: public class StringReverse public static String reverse(string text) //TODO public static String reverse2(string text) //TODO public static void main(string[] args) System.out.println("reverse-recursive:") System.out.println(StringReverse.reverse("Hello!")); System.out.println("Expected:!olleH"); System.out.println(StringReverse.reverse("Odd")); System.out.println("Expected: ddo"); System.out.println("reverse-iterative:") System.out.println(StringReverse.reverse2("Hello!")); System.out.println("Expected:!olleH"); System.out.println(StringReverse.reverse2("Odd")); System.out.println("Expected: ddo"); Answer: public class StringReverse public static String reverse(string text) //10 points if (text.length() <= 1) return text; char c = text.charat(0); String rest = new String(text.substring(1)); String reversetext = reverse(rest) + c; return reversetext; public static String reverse2(string text) //10 points if (text.length() <= 1) return text; String reversetext = ""; for (int i = text.length() - 1; i >= 0; i--)

5 char c = text.charat(i); reversetext = reversetext + c; return reversetext; public static void main(string[] args) System.out.println("reverse-recursive:") System.out.println(StringReverse.reverse("Hello!")); System.out.println("Expected:!olleH"); System.out.println(StringReverse.reverse("Odd")); System.out.println("Expected: ddo"); System.out.println("reverse-iterative:") System.out.println(StringReverse.reverse2("Hello!")); System.out.println("Expected:!olleH"); System.out.println(StringReverse.reverse2("Odd")); System.out.println("Expected: ddo"); Q2. [30 points] LinearSearch.java Write a program LinearSearch that implements a method to search a value(key) in an array by scanning through elements left to right in a linear fashion. If the key is found its index should be return, otherwise -1 should be returned. Provide: 1. Iterative linear search method linearsearch(int key) 2. Recursive linear search method recursivelinearsearch(int key) Use following class template: import java.util.random; import java.util.scanner; import java.util.arrays; public class LinearArray private int[] data; // array of values private static Random generator = new Random(); public LinearArray( int size ) //populate array with random values in range data = new int[ size ]; for ( int i = 0; i < size; i++ ) data[ i ] = 10 + generator.nextint( 90 ); public String tostring() return Arrays.toString(data); /*Recursive method*/ public int recursivelinearsearch( int search, int start )

6 //TODO /*Iterative method*/ public int linearsearch( int searchkey ) //TODO public static void main( String[] args ) Scanner input = new Scanner( System.in ); int key; // search key int index; // location of search key in array // create array and output it LinearArray searcharray = new LinearArray( 10 ); System.out.println( searcharray + "\n" ); // print array // get input from user System.out.print( "Please enter an integer value (-1 to quit): " ); key = input.nextint(); // read first int from user // recursive search index = searcharray.recursivelinearsearch( key,0 ); System.out.println("Recursive search:"); if ( index == -1 ) // integer was not found System.out.println( "The integer " + key + " was not found.\n" ); else // integer was found System.out.println( "The integer " + key + " was found in index " + index + ".\n" ); //iterative search index = searcharray.linearsearch( key ); System.out.println("Iterative search:"); if ( index == -1 ) // integer was not found System.out.println( "The integer " + key + " was not found.\n" ); else // integer was found System.out.println( "The integer " + key + " was found in index " + index + ".\n" ); // end main Answer: import java.util.random; import java.util.scanner; import java.util.arrays; public class LinearArray private int[] data; // array of values private static Random generator = new Random(); public LinearArray( int size )

7 //populate array with random values in range data = new int[ size ]; for ( int i = 0; i < size; i++ ) data[ i ] = 10 + generator.nextint( 90 ); public String tostring() return Arrays.toString(data); /*Recursive method*/ public int recursivelinearsearch( int search, int start ) //20 points int location; // variable to store return value if ( start >= data.length ) // BASE CASE1: value not found location = -1; else if ( data[ start ] == search )// BASE CASE2: if item is equal to search key,return current location location = start; else location = recursivelinearsearch( search, start + 1 ); // RECURSIVE STEP return location; // return location of search key /*Iterative method*/ public int linearsearch( int searchkey ) //10 points // loop through array sequentially for ( int index = 0; index < data.length; index++ ) if ( data[ index ] == searchkey ) return index; // return index of integer return -1; // integer was not found // end method linearsearch public static void main( String[] args ) Scanner input = new Scanner( System.in ); int key; // search key int index; // location of search key in array // create array and output it LinearArray searcharray = new LinearArray( 10 ); System.out.println( searcharray + "\n" ); // print array // get input from user System.out.print( "Please enter an integer value (-1 to quit): " ); key = input.nextint(); // read first int from user // recursive search index = searcharray.recursivelinearsearch( key,0 ); System.out.println("Recursive search:"); if ( index == -1 ) // integer was not found System.out.println( "The integer " + key + " was not found.\n" );

8 else // integer was found System.out.println( "The integer " + key + " was found in index " + index + ".\n" ); //iterative search index = searcharray.linearsearch( key ); System.out.println("Iterative search:"); if ( index == -1 ) // integer was not found System.out.println( "The integer " + key + " was not found.\n" ); else // integer was found System.out.println( "The integer " + key + " was found in index " + index + ".\n" ); // end main Note: Marks will be assigned for proper comments and output. In addition to comments in your program, also include a file header comment at the top of each program file that includes your name, assignment number, and a description of the program: //********************************************************** // AssignmentNo (Enter Assignment number): (Enter ClassName) // Author(s): (Enter your full name here) // Description: (Enter Description) //********************************************************* Online Submission Instructions: Copy the folder <<yourname>>asg3 (e.g. JohnDoeAsg3) containing answer files, into /usr/people/handin/cs160 before midnight of the date indicated in class website.