Java*

Part I: Class Names (10 point)

------------------------------- Class Names implements some preliminary actions on names and initials. Create an empty project in Eclipse and call it Names. Add class: Names then compile and run the code.

The program has an error. What is the method (i.e., procedure) that generated an error? What is the line number within the file Names.java?

The error is in one of the methods in the String class, which is a standard Java library. When you think you have found the error, correct it, save the file, recompile it, and execute it to see if the problem is solved.

/* Fraction.java */ import java.io.*; /** The Fraction class implements nonnegative fractions (rational numbers). */ class Fraction { /* private fields within a Fraction. */ private int numberOfFractions = 0; private int numerator; private int denominator; /** Constructs a Fraction n/d. * @param n is the numerator. Must be nonnegative. * @param d is the denominator. Must be positive. */ public Fraction(int n, int d) { if (n < 0) { System.out.println("Fatal error: Negative numerator."); System.exit(0); } if (d < 1) { System.out.println("Fatal error: Nonpositive denominator."); System.exit(0); } numberOfFractions++; numerator = n; denominator = d; } /** Constructs a Fraction n/1. * @param n is the numerator. Must be nonnegative. */ public Fraction(int n) { this(n, 1); } /** Constructs a Fraction 0/1. */ public Fraction() { numberOfFractions++; numerator = 0; denominator = 1; } /** Copies the Fraction "original". */ public Fraction(Fraction original) { numberOfFractions++; numerator = 0; denominator = 1; } /** Converts this Fraction to a string format: "numerator/denominator." * Fractions should be printed in reduced form (part of your assignment is * to make this true). * @return a String representation of this Fraction. */ public String toString() { int thisGcd = gcd(numerator, denominator); return (numerator / thisGcd + "/" + denominator / thisGcd); } /** Return the sum of two fractions. * @param f2 is the Fraction to be added. * @return the result of adding f2 to this Fraction. */ public Fraction add(Fraction f2) { Fraction r = new Fraction((numerator * f2.denominator) + (f2.numerator * denominator), denominator * f2.denominator); return r; } /** Replaces this Fraction's numerator with a new value. * @param numerator is the new numerator. Must be nonnegative. */ public void changeNumerator(int numerator) { // DO NOT CHANGE THIS SIGNATURE! // Fix the bug that prevents this method from working correctly. if (numerator < 0) { System.out.println("Fatal error: Negative numerator."); System.exit(0); } numerator = numerator; } /** Returns the number of Fraction objects in existence. * @return the number of Fraction objects in existence. */ public int fracs() { // DO NOT CHANGE THIS SIGNATURE! // Fix the bug that prevents this method from working correctly. return numberOfFractions; } /** Computes the greatest common divisor (gcd) of the two inputs. * @param x must be nonnegative * @param y must be nonnegative * @return the gcd of x and y */ static private int gcd(int x, int y) { /* Replace the following line with your solution. */ return 1; } /** Put the Fraction class through some tests. * @param argv is not used. */ public static void main(String[] argv) { /* Test all four contructors and toString. */ Fraction f0 = new Fraction(); Fraction f1 = new Fraction(3); Fraction f2 = new Fraction(12, 20); Fraction f3 = new Fraction(f2); System.out.println(" Testing constructors and toString():"); System.out.println("The fraction f0 is " + f0.toString()); System.out.println("The fraction f1 is " + f1); // toString is implicit. System.out.println("The fraction f2 is " + f2); System.out.println("The fraction f3 is " + f3 + ", which should equal f2"); /* Test the add method. */ System.out.println(" Testing add:"); /* Fraction sumOfTwo = _______________; // Sum of f1 and f2. Fraction sumOfThree = ______________; // Sum of f0, f1, and f2. System.out.println("The sum of " + f1 + " and " + f2 + " is " + sumOfTwo); System.out.println("The sum of " + f0 + ", " + f1 + " and " + f2 + " is " + sumOfThree); */ /* Test the methods used in Part III. */ System.out.println(" Testing changeNumerator and fracs:"); f3.changeNumerator(7); System.out.println("Now f3 is " + f3 + ", which should be 7/20"); System.out.println("The total number of Fraction objects is " + f3.fracs()); /* Test gcd function (static method). */ System.out.println(" Testing gcd:"); System.out.println("The gcd of 2 and 10 is: " + gcd(2, 10)); System.out.println("The gcd of 15 and 5 is: " + gcd(15, 5)); System.out.println("The gcd of 24 and 18 is: " + gcd(24, 18)); System.out.println("The gcd of 10 and 10 is: " + gcd(10, 10)); System.out.println("The gcd of 21 and 400 is: " + gcd(21, 400)); } }

/* Names.java */ import java.io.*; /** The Names class provides a single function, main, that will * perform various manipulations of the name John Fitzgerald Kennedy. * This is a modification of the program on page 43 of Arnow and Weiss. */ class Names { /** Performs various string operations on the name John Fitzgerald Kennedy. * @param arg is not used. */ public static void main(String arg[]) { String first = "John"; String middle = "Fitzgerald"; String last = "Kennedy"; String initials; String firstInit, middleInit, lastInit; firstInit = first.substring(0,1); middleInit = middle.substring(0,1); lastInit = last.substring(0,1); initials = firstInit.concat(middleInit); initials = initials.concat(lastInit); System.out.println() System.out.println(first + " " + middle + " " + last + " "); System.out.println(initials); System.out.println(last + ", " + first + " " + middle); System.out.println(last + ", " + first + " " + middleInit +"."); System.out.println(first.toUpperCase() + " " + last.toUpperCase); System.out.println(first + " equals john is " + first.equals("john")); System.out.println(first + " equals john (ignoring case) is " + first.equalsIgnoreCase("john")); System.out.println("The character at index 3 in " + middle + " is " + middle.substring(3,1)); System.out.println("The index of \"gerald\" within " + middle + " is " + middle.indexOf("gerald")); System.out.println("The index of \"gerald\" within " + last + " is " + last.indexOf("gerald")); System.out.println(); } }