《Java语言程序设计(基础篇)》(第10版 梁勇 著)第五章练习题答案

《Java语言程序设计（基础篇）》（第10版梁勇著）第五章练习题答案5.1public class Exercise05_01 {public static void main(String[] args) {int countPositive = 0, countNegative = 0;int count = 0, total = 0, num;Scanner input = new Scanner(System.in);System.out.print("Enter integers ending with 0: ");num = input.nextInt();while (num != 0) {if (num > 0)countPositive++;else if (num < 0)countNegative++;total += num;count++;// Read the next numbernum = input.nextInt();}if (count == 0)System.out.println("no numbers are entered except 0");else {System.out.println("The number of positives is " + countPositive); System.out.println("The number of negatives is " + countNegative); System.out.println("The total is " + total);System.out.println("The average is " + total * 1.0 / count);}}}5.1附加public class Exercise05_01Extra {public static void main(String[] args) {final int NUMBER_OF_TRIALS = 10000000;int numberOfHits = 0;for (int i = 0; i < NUMBER_OF_TRIALS; i++) {double x = Math.random() * 2.0 - 1;double y = Math.random() * 2.0 - 1;if (x * x + y * y <= 1)numberOfHits++;}double pi = 4.0 * numberOfHits / NUMBER_OF_TRIALS;System.out.println("PI is " + pi);}}5.2public class Exercise05_02 {public static void main(String[] args) {int correctCount = 0; // Count the number of correct answersint count = 0; // Count the number of questionsjava.util.Scanner input = new java.util.Scanner(System.in);long startTime = System.currentTimeMillis();while (count < 10) {// 1. Generate two random single-digit integersint number1 = 1 + (int)(Math.random() * 15);int number2 = 1 + (int)(Math.random() * 15);// 2. Prompt the student to answer 搘hat is number1 ?number2??System.out.print("What is " + number1 + " + " + number2 + "? ");int answer = input.nextInt();// 3. Grade the answer and display the resultString replyString;if (number1 + number2 == answer) {replyString = "You are correct!";correctCount++;}else {replyString = "Your answer is wrong.\n" + number1 + " + "+ number2 + " should be " + (number1 + number2);}System.out.println(replyString);// Increase the countcount++;}System.out.println("Correct count is " + correctCount);long endTime = System.currentTimeMillis();System.out.println("Time spent is " + (endTime - startTime) / 1000 + " seconds");}}5.2附加public class Exercise05_02Extra {public static void main(String[] args) {final int NUMBER_OF_TRIALS = 1000000;int numberOfHits = 0;for (int i = 0; i < NUMBER_OF_TRIALS; i++){double x = Math.random() * 2.0 - 1;double y = Math.random() * 2.0 - 1;if (x < 0)numberOfHits += 1;else if (!(x > 1 || x < 0 || y > 1 || y < 0)) {double slope = (1.0 - 0) / (0 - 1.0);double x1 = x + -y * slope;if (x1 <= 1)numberOfHits += 1;}}System.out.println("The probability in Region 1 and 3 is " +(1.0 * numberOfHits / NUMBER_OF_TRIALS));}/*static boolean isInRegion3(double x, double y) {if (x > 1 || x < 0 || y > 1 || y < 0)return false;else {double slope = (1.0 - 0) / (0 - 1.0);double x1 = x + -y * slope;if (x1 <= 1)return true;elsereturn false;}}*/}5.3public class Exercise05_03 {public static void main(String[] args) {System.out.printf("%-14s%-10s\n", "Kilograms", "Pounds");System.out.println("--------------------");int kilograms = 1;while (kilograms < 200) {System.out.printf("%-14d%-10.1f\n", kilograms, kilograms * 2.2); kilograms += 2;}/** Alternatively use for loopfor (int kilograms = 1; kilograms <= 199; kilograms += 2) {System.out.println(kilograms + "\t\t" + kilograms * 2.2);}*/}}5.3附加public class Exercise05_03Extra {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter the number of seconds: ");int numberOfSeconds = input.nextInt();long currentTime = System.currentTimeMillis() / 1000;long endTime = currentTime + numberOfSeconds * 1000;while (currentTime <= endTime) {if ((endTime - currentTime) % 1000 == 0) {if (endTime - currentTime > 1000)System.out.println((endTime - currentTime) / 1000 + " secondsremaining");else if (endTime - currentTime == 1000)System.out.println("1 second remaining");}currentTime += 1;}System.out.println("Stopped");}}5.4public class Exercise05_04 {public static void main(String[] args) {System.out.println("Miles\t\tKilometers");System.out.println("-------------------------------");// Use while loopint miles = 1;while (miles <= 10) {System.out.println(miles + "\t\t" + miles * 1.609);miles++;}/** Alternatively use for loopfor (int miles = 1; miles <= 10; miles++) {System.out.println(miles + "\t\t" + miles * 1.609);}*/}}5.4附加public class Exercise05_04Extra {public static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);while (true) {System.out.println("Main menu");System.out.println("1: Addition");System.out.println("2: Subtraction");System.out.println("3: Multiplication");System.out.println("4: Division");System.out.println("5: Exit");System.out.print("Enter a choice: ");int choice = input.nextInt();int number1 = (int)(Math.random() * 10);int number2 = (int)(Math.random() * 10);int answer;if (choice == 1) {System.out.print("What is " + number1 + " + " + number2 + "? "); answer = input.nextInt();if (number1 + number2 == answer)System.out.println("Correct");elseSystem.out.println("Your answer is wrong. The correct answer is " + (number1 + number2));}else if (choice == 2) {if (number1 < number2) { // Swap number1 with number2int temp = number1;number1 = number2;number2 = temp;}System.out.print("What is " + number1 + " - " + number2 + "? "); answer = input.nextInt();if (number1 - number2 == answer)System.out.println("Correct");elseSystem.out.println("Your answer is wrong. The correct answer is " + (number1 - number2));}else if (choice == 3) {System.out.print("What is " + number1 + " * " + number2 + "? "); answer = input.nextInt();if (number1 * number2 == answer)System.out.println("Correct");elseSystem.out.println("Your answer is wrong. The correct answer is " + (number1 * number2));}else if (choice == 4) {while (number2 == 0)number2 = (int)(Math.random() * 10);System.out.println("What is " + number1 + " / " + number2 + "? "); answer = input.nextInt();if (number1 / number2 == answer)System.out.println("Correct");elseSystem.out.println("Your answer is wrong. The correct answer is " + (number1 / number2));}else if (choice == 5)break;}}}5.5public class Exercise05_05 {public static void main(String[] args) {System.out.printf("%10s%10s | %10s%10s\n", "kilograms", "pounds", "pounds", "kilograms");System.out.println("---------------------------------------------");// Use while loopint kilograms = 1;int pounds = 20;int count = 1;while (count <= 100) {System.out.printf("%10d%10.3f | %10d%10.3f\n", kilograms,kilograms * 2.2, pounds, pounds / 2.2);kilograms += 2;pounds += 5;count++;}/*** Alternatively use for loop int kilograms = 1; int pounds = 20; for (int * count = 1; count <= 100; kilograms += 2, pounds += 5, count++) {* System.out.println(kilograms + "\t\t" + kilograms * 2.2 + "\t|\t" + * pounds + "\t\t" + pounds / 2.2); }*/}}5.5附加public class Exercise05_05Extra {public static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);System.out.print("Enter the number of sides: ");int n = input.nextInt();System.out.print("Enter the radius of the bounding circle: ");double radius = input.nextDouble();double angle = 0;System.out.print("The coordinates of the points on the polygon are ");for (int i = 0; i < n; i++) {double x = radius * Math.cos(angle);double y = radius * Math.sin(angle);System.out.println("(" + x + ", " + y + ")");angle += 2 * Math.PI / n;}}}5.6public class Exercise05_06 {public static void main(String[] args) {System.out.printf("%10s%10s | %10s%10s\n", "Miles", "Kilometers", "Kilometers", "Miles");System.out.println("---------------------------------------------");// Use while loopint miles = 1;int kilometers = 20;int count = 1;while (count <= 10) {System.out.printf("%10d%10.3f | %10d%10.3f\n", miles, miles * 1.609,kilometers, kilometers / 1.609);miles++;kilometers += 5;count++;}/** Use for loop int miles = 1; int kilometers = 20; for (int count = 1; * count <= 10; miles++, kilometers += 5, count++) {* System.out.printf("%10d%10.3f | %10d%10.3f\n", miles, miles * 1.609,* kilometers, kilometers / 1.609); }*/}}5.6附加public class Exercise05_06Extra {public static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);System.out.print("Enter a genome string: ");String genome = input.nextLine();boolean found = false;int start = -1;for (int i = 0; i < genome.length() - 2; i++) {String triplet = genome.substring(i, i + 3);if (triplet.equals("ATG"))start = i + 3;else if ((triplet.equals("TAG") || triplet.equals("TAA") || triplet .equals("TGA")) && start != -1) {// A possible gene is foundString gene = genome.substring(start, i);if (gene.length() % 3 == 0) {// A gene is found and display the genefound = true;System.out.println(gene);start = -1; // Start to find the next gene in the genome}}}if (!found)System.out.println("no gene is found");}}5.7public class Exercise05_07 {public static void main(String[] args) {// Use a while loopdouble tuition = 10000;int count = 1;while (count <= 10) {tuition = tuition * 1.05;count++;}/*// Alternatively use a for loopdouble tuition = 10000;for (int i = 1; i <= 10; i++) {tuition = tuition * 1.05;}*/System.out.println("Tuition in ten years is " + tuition);double sum = tuition;for (int i = 2; i <= 4; i++) {tuition = tuition * 1.05;sum += tuition;}System.out.println("The four-year tuition in ten years is " + sum); }}5.7附加public class Exercise05_07Extra {public static void main(String[] args) {System.out.print("Enter a positive integer: ");Scanner input = new Scanner(System.in);int n = input.nextInt();int number = n;int factor = 2;int coefficient = 1;while (factor <= number) {if (number % (factor * factor) == 0) {coefficient *= factor;number = number / (factor * factor);}elsefactor++;}System.out.print("sqrt(" + n + ") is ");if (n == 1)System.out.println(1);else {if (coefficient > 1)System.out.print(coefficient);if (coefficient > 1 && number > 1)System.out.print("*");if (number > 1)System.out.print("sqrt(" + number + ")");}}}5.8public class Exercise05_08 {public static void main(String[] args) {Scanner input = new Scanner(System.in);// Prompt the user to enter the number of students System.out.print("Enter the number of students: ");int numOfStudents = input.nextInt();System.out.print("Enter a student name: ");String student1 = input.next();System.out.print("Enter a student score: ");double score1 = input.nextDouble();for (int i = 0; i < numOfStudents - 1; i++) {System.out.print("Enter a student name: ");String student = input.next();System.out.print("Enter a student score: ");double score = input.nextDouble();if (score > score1) {student1 = student;score1 = score;}}System.out.println("Top student " +student1 + "'s score is " + score1);}}5.8附加public class Exercise05_08Extra {public static void main(String[] args) {String vehiclePlateNumber = "";for (int i = 0; i < 7; i++) {char ch = Math.random() < 0.5 ?(char)('A' + (int)(Math.random() * 26)) : (char)('0' + (int)(Math.random() * 10));vehiclePlateNumber += ch;}System.out.println("A random vehicle plate number: "+ vehiclePlateNumber);}}5.9public class Exercise05_09 {public static void main(String[] args) {Scanner input = new Scanner(System.in);// Prompt the user to enter the number of studentsSystem.out.print("Enter the number of students: ");int numberOfStudents = input.nextInt();System.out.print("Enter a student name: ");String student1 = input.next();System.out.print("Enter a student score: ");double score1 = input.nextDouble();System.out.print("Enter a student name: ");String student2 = input.next();System.out.print("Enter a student score: ");double score2 = input.nextDouble();// Make sure that student1 is for the highest// and student2 is for the second highestif (score1 < score2) {// SwapString tempString = student1;double tempScore = score1;student1 = student2;score1 = score2;student2 = tempString;score2 = tempScore;}for (int i = 0; i < numberOfStudents - 2; i++) {System.out.print("Enter a student name: ");String student = input.next();System.out.print("Enter a student score: ");double score = input.nextDouble();if (score > score1) {student2 = student1; // student1 now is the second highestscore2 = score1;student1 = student; // new student becomes the highestscore1 = score;}else if (score > score2) {student2 = student; // new student becomes the second highest score2 = score;}}System.out.println("Top two students:");System.out.println(student1 + "'s score is " + score1);System.out.println(student2 + "'s score is " + score2);}}5.9附加public class Exercise05_09Extra {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter a string: ");String s = input.nextLine();int count = 0;for (int i = 0; i < s.length() - 1; i++)if (s.charAt(i) == s.charAt(i + 1))count++;System.out.println("The number of consecutive repeating characters is " + count);}}5.10public class Exercise05_10 {public static void main(String[] args) {int count = 1;for (int i = 100; i <= 1000; i++)if (i % 5 == 0 && i % 6 == 0)System.out.print((count++ % 10 != 0) ? i + " ": i + "\n");}}5.10附加public class Exercise05_10Extra {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter a string: ");String s = input.nextLine();int maxOccurrenceCount = 1;char maxOccurrenceChar = s.charAt(0);int currentOccurrenceCount = 1;char currentCh = s.charAt(0);for (int i = 0; i < s.length() - 1; i++) {if (currentCh == s.charAt(i + 1))currentOccurrenceCount++;if (currentCh != s.charAt(i + 1) ||(i == s.length() - 2 && currentCh == s.charAt(i + 1))){if (currentOccurrenceCount > maxOccurrenceCount) {maxOccurrenceCount = currentOccurrenceCount;maxOccurrenceChar = currentCh;}currentCh = s.charAt(i + 1);currentOccurrenceCount = 1;}}System.out.print("The first longest consecutive repeating character substring is ");for (int i = 0; i < maxOccurrenceCount; i++)System.out.print(maxOccurrenceChar);}}5.11public class Exercise05_11 {public static void main(String[] args) {int count = 1;int i = 100;while (i <= 200) {if (i % 5 == 0 ^ i % 6 == 0) {System.out.print((count % 10 != 0) ? i + " ": i + "\n");count++;}i++;}/* for loopfor (int i = 100; i <= 200; i++)if (i % 5 == 0 ^ i % 6 == 0)System.out.print((count++ % 10 != 0) ? i + " ": i + "\n"); */}}5.11附加public class Exercise05_11Extra {public static void main(String[] args) {System.out.printf("%-15s%-15s\n", "RealNumber", "SquareRoot"); System.out.println("-------------------------------");for (int num = 0; num <= 20; num++) {System.out.printf("%-15d%-15.4f\n", num, Math.sqrt(num));}}}5.12/** Find the smallest number such that n*n < 12000 */public class Exercise05_12 {// Main methodpublic static void main(String[] args) {int i = 1;while (i * i <= 12000 ) {i++;}System.out.println("This number is " + i);}}5.12附加public class Exercise05_12Extra {public static void main(String[] args) {System.out.println("Degree\tSin\t\tCos");for (int degree = 0; degree <= 360; degree += 10) {System.out.printf("%-3d\t%6.4f\t\t%6.4f\n", degree,Math.sin(degree * Math.PI / 180),Math.cos(degree * Math.PI / 180));}}/*public static double format(double d, int position) {return Math.round(d * Math.pow(10, position)) / Math.pow(10, position); } */}5.13/** Finding the largest n such that n^3 < 12000) */public class Exercise05_13 {public static void main(String[] args) {int i = 1;while (i * i * i < 12000) {i++;}// i^3 >= 12000// (i-1)^3 < 12000System.out.println("This number is " + (i - 1));}}5.13附加public class Exercise05_13Extra {public static void main(String[] args) {for (int i = 0; i < 10; i++) {System.out.println((int)(Math.random() * 101));}}}5.14public class Exercise05_14 {public static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);// Enter n1System.out.print("Enter the first number: ");int n1 = input.nextInt();// Enter n2System.out.print("Enter the second number: ");int n2 = input.nextInt();int d = (n1 < n2) ? n1 : n2;for (; d >= 1; d--) {if ((n1 % d == 0) && (n2 % d == 0)) {break;}}System.out.println("GCD of " + n1 + " and " + n2 + " is "+ d);}}5.14附加public class Exercise05_14Extra {public static void main(String[] args) {double value = Math.random();while (value <= 0.75) {System.out.println(value);value = Math.random();}System.out.println(value);}}5.15public class Exercise05_15 {public static void main(String[] args) {int count = 1;for (int i = '!'; i < '~'; i++) {System.out.print((count++ % 10 != 0) ? (char)i + " " :(char)i + "\n");}}}5.16public class Exercise05_16 {// Main methodpublic static void main(String args[]) {java.util.Scanner input = new java.util.Scanner(System.in);// Prompt the user to enter a positive integerSystem.out.print("Enter a positive integer: ");int number = input.nextInt();// Find all the smallest factors of the integerSystem.out.println("The factors for " + number + " is");int factor = 2;while (factor <= number) {if (number % factor == 0) {number = number / factor;System.out.println(factor);}else {factor++;}}}}5.17public class Exercise05_17 {public static void main(String[] args) {// Create a ScannerScanner input = new Scanner(System.in);// Prompt the user to enter the number of linesSystem.out.print("Enter the number of lines: ");int numberOfLines = input.nextInt();if (numberOfLines < 1 || numberOfLines > 15) {System.out.println("You must enter a number from 1 to 15"); System.exit(1);}// Print linesfor (int row = 1; row <= numberOfLines; row++) {// Print (NUMBER_OF_LINES ?row) leading spacesfor (int column = 1; column <= numberOfLines - row; column++) System.out.print(" ");// Print leading numbers row, row ?1, ..., 1for (int num = row; num >= 1; num--)System.out.print((num >= 10) ? " " + num : " " + num);// Print ending numbers 2, 3, ..., row ?1, rowfor (int num = 2; num <= row; num++)System.out.print((num >= 10) ? " " + num : " " + num);// Start a new lineSystem.out.println();}}}5.18public class Exercise05_18 {/** Print Pattern I */public static void main(String[] args) {for (int i = 1; i <= 6; i++) {for (int j = 1; j <= i; j++)System.out.print(j + " ");System.out.println();}}}解法2：public class Exercise05_18d {/** Print Pattern D */public static void main(String[] args) {for (int i = 1; i <= 6; i++) {for (int j = 1; j <= 6; j++)System.out.print(i <= j ? j + " " : " ");System.out.println();}}}5.19public class Exercise05_19 {public static void main(String[] args) {int number = 0; // Number to printfor (int row = 0; row <= 7; row++) {// Pad leading blanksfor (int col = 1; col <= 7 - row; col++)System.out.printf("%4s", " ");// Print left half of the rowfor (int col = 0; col <= row; col++) {number = (int)Math.pow(2, col);System.out.printf("%4d", number);}// Print the right half of the rowfor (int col = row - 1; col >= 0; col--) {number = (int)Math.pow(2, col);System.out.printf("%4d", number);}// Start a new lineSystem.out.print('\n');}}}5.20public class Exercise05_20 {// Main methodpublic static void main(String[] args) {int count = 1; // Count the number of prime numbersint number = 2; // A number to be tested for primenessboolean isPrime = true; // If the current number is prime?System.out.println("The prime numbers from 2 to 1000 are \n");// Repeatedly test if a new number is primewhile (number <= 1000) {// Assume the number is primeisPrime = true;// Set isPrime to false, if the number is primefor (int divisor = 2; divisor <= number / 2; divisor++) {if (number % divisor == 0) { // If true, the number is prime isPrime = false;break; // Exit the for loop}}// Print the prime number and increase the countif (isPrime) {if (count%8 == 0) {// Print the number and advance to the new lineSystem.out.println(number);}elseSystem.out.print(number + " ");count++; // Increase the count}// Check if the next number is primenumber++;}}}5.21public class Exercise05_21 {// Main methodpublic static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);// Enter loan amountSystem.out.print("Enter loan amount, for example 120000.95: ");double loanAmount = input.nextDouble();// Enter number of yearsSystem.out.print("Enter number of years as an integer, \nfor example 5: ");// Convert string to intint numOfYears = input.nextInt();// Display the headerSystem.out.printf("%-20s%-20s%-20s\n", "Interest Rate", "Monthly Payment", "Total Payment");for (double annualInterestRate = 5.0; annualInterestRate <= 8.0;annualInterestRate += 1.0 / 8) {// Obtain monthly interest ratedouble monthlyInterestRate = annualInterestRate / 1200;// Compute mortgagedouble monthlyPayment = loanAmount * monthlyInterestRate /(1 - (Math.pow(1 / (1 + monthlyInterestRate), numOfYears * 12)));double totalPayment = monthlyPayment * numOfYears * 12;// Display resultsSystem.out.printf("%5.3f%c %20.2f %20.2f\n", annualInterestRate, '%', monthlyPayment, totalPayment);}}}5.22public class Exercise05_22 {public static void main(String[] args) {java.util.Scanner input = new java.util.Scanner(System.in);// Enter loan amountSystem.out.print("Enter loan amount, for example 120000.95: ");double loanAmount = input.nextDouble();// Enter number of yearsSystem.out.print("Enter number of years as an integer, for example 5: ");int numOfYears = input.nextInt();// Enter yearly interest rateSystem.out.print("Enter yearly interest rate, for example 8.25: ");double annualInterestRate = input.nextDouble();// Obtain monthly interest ratedouble monthlyInterestRate = annualInterestRate/1200;// Compute mortgagedouble monthlyPayment = loanAmount*monthlyInterestRate /(1 - (Math.pow(1 / (1 + monthlyInterestRate), numOfYears * 12)));double balance = loanAmount;double interest;double principal;System.out.println("Monthly Payment: " + (int)(monthlyPayment * 100) / 100.0 );System.out.println("Total Payment: " + (int)(monthlyPayment * 12 * numOfYears * 100) / 100.0 + "\n" );// Display the headerSystem.out.println("Payment#\tInterest\tPrincipal\tBalance");for (int i = 1; i <= numOfYears * 12; i++) {interest = (int)(monthlyInterestRate * balance * 100) / 100.0;principal = (int)((monthlyPayment - interest) * 100) / 100.0;balance = (int)((balance - principal) * 100) / 100.0;System.out.println(i + "\t\t" + interest+ "\t\t" + principal + "\t\t" + balance);}}}5.23public class Exercise05_23 {final static int N = 50000;public static void main (String[] args) {// Backward computingdouble sum = 0.0;for (int i = N; i >= 1; i--)sum += 1.0 / (double)(i);System.out.println("The result of the backward computation " + sum);// Forward computingdouble sum1 = 0.0;for (int i = 1; i <= N; i++)sum1 += 1.0 / (double)(i);System.out.println("The result of the forward computation " + sum1);double difference = sum - sum1;System.out.println("difference is " + difference);}/*public static double backward() {double sum = 0.0;for (int i = N; i >= 1; i--)sum += 1.0 / (double)(i);return sum;}static double forward() {double sum = 0.0;for (int i = 1; i <= N; i++)sum += 1.0 / (double)(i);return sum;} */}5.24public class Exercise05_24 {public static void main(String[] args) {double sum = 0;for (int i = 1; i <= 97; i += 2)sum += 1.0 * i / (i + 2);System.out.println("sum is " + sum);}}5.25public class Exercise05_25 {public static void main(String[] args) {double pi = 1;。