《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

5.1

public 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 number

num = 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);

}

}

5.2

public class Exercise05_02 {

public static void main(String[] args) {

int correctCount = 0; // Count the number of correct answers

int count = 0; // Count the number of questions

java.util.Scanner input = new java.util.Scanner(System.in);

long startTime = System.currentTimeMillis();

while (count < 10) {

// 1. Generate two random single-digit integers

int 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 result

String 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 count

count++;

}

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;

else

return false;

}

}

*/

}

5.3

public 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 loop

for (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 + " seconds

remaining");

else if (endTime - currentTime == 1000)

System.out.println("1 second remaining");

}

currentTime += 1;

}

System.out.println("Stopped");

}

}

5.4

public class Exercise05_04 {

public static void main(String[] args) {

System.out.println("Miles\t\tKilometers");

System.out.println("-------------------------------");

// Use while loop

int miles = 1;

while (miles <= 10) {

System.out.println(miles + "\t\t" + miles * 1.609);

miles++;

}

/** Alternatively use for loop

for (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");

else

System.out.println("Your answer is wrong. The correct answer is " + (number1 + number2));

}

else if (choice == 2) {

if (number1 < number2) { // Swap number1 with number2

int temp = number1;

number1 = number2;

number2 = temp;

}

System.out.print("What is " + number1 + " - " + number2 + "? "); answer = input.nextInt();

if (number1 - number2 == answer)

System.out.println("Correct");

else

System.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");

else

System.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");

else

System.out.println("Your answer is wrong. The correct answer is " + (number1 / number2));

}

else if (choice == 5)

break;

}

}

}

5.5

public 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 loop

int 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;

}

}

}

5.6

public 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 loop

int 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 found

String gene = genome.substring(start, i);

if (gene.length() % 3 == 0) {

// A gene is found and display the gene

found = 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");

}

}

5.7

public class Exercise05_07 {

public static void main(String[] args) {

// Use a while loop

double tuition = 10000;

int count = 1;

while (count <= 10) {

tuition = tuition * 1.05;

count++;

}

/*

// Alternatively use a for loop

double 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);

}

else

factor++;

}

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 + ")");

}

}

}

5.8

public 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);

}

}

5.9

public class Exercise05_09 {

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 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 highest

if (score1 < score2) {

// Swap

String 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 highest

score2 = score1;

student1 = student; // new student becomes the highest

score1 = 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);

}

}

5.10

public 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);

}

}

5.11

public 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 loop

for (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 method

public 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 < 12000

System.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));

}

}

}

5.14

public class Exercise05_14 {

public static void main(String[] args) {

java.util.Scanner input = new java.util.Scanner(System.in);

// Enter n1

System.out.print(

"Enter the first number: ");

int n1 = input.nextInt();

// Enter n2

System.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);

}

}

5.15

public 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");

}

}

}

5.16

public class Exercise05_16 {

// Main method

public static void main(String args[]) {

java.util.Scanner input = new java.util.Scanner(System.in);

// Prompt the user to enter a positive integer

System.out.print(

"Enter a positive integer: ");

int number = input.nextInt();

// Find all the smallest factors of the integer

System.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++;

}

}

}

}

5.17

public class Exercise05_17 {

public static void main(String[] args) {

// Create a Scanner

Scanner input = new Scanner(System.in);

// Prompt the user to enter the number of lines

System.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 lines

for (int row = 1; row <= numberOfLines; row++) {

// Print (NUMBER_OF_LINES ?row) leading spaces

for (int column = 1; column <= numberOfLines - row; column++) System.out.print(" ");

// Print leading numbers row, row ?1, ..., 1

for (int num = row; num >= 1; num--)

System.out.print((num >= 10) ? " " + num : " " + num);

// Print ending numbers 2, 3, ..., row ?1, row

for (int num = 2; num <= row; num++)

System.out.print((num >= 10) ? " " + num : " " + num);

// Start a new line

System.out.println();

}

}

}

5.18

public 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++)