《Java语言程序设计(基础篇)(原书第10版)》第2~4章部分编程练习题代码
这内容只包括本人在上《Java语言程序设计》这门课时老师布置的题目。因此，这部分代码只是原书的一小部分编程题。
例：（2.6）意思是：第2章的第6题。
（2.6）（求一个整数各位数的和）
package javahomework;
import java.util.Scanner;
public class java0206 {
public static void main (String[] args) {
//Create a Scanner object
Scanner input =new Scanner(System.in);
System.out.print("Enter a number between 0 and 1000:");
int number = input.nextInt();
int a = number/1000;//判断千位数
int b = number/100-a*10;//统计百位数
int c = number/10-a*100-b*10;//统计十位数
int d = number-a*1000-b*100-c*10;//统计个位数
int s = a+b+c+d;//求各个位数的总和
System.out.println("The sum of the digit is "+ s );
}
}
（2.10）（科学：计算能量）
package javahomework;
import java.util.Scanner;
public class java0210 {
public static void main (String[] args) {
//Create a Scanner object
Scanner input =new Scanner(System.in);
System.out.print("Enter the amount of water in kilograms:");
double number1 = input.nextDouble();
System.out.print("Enter the initial temperature:");
double number2 = input.nextDouble();
System.out.print("Enter the final temperature:");
double number3 = input.nextDouble();
double Q = number1*(number3-number2)*4184;
System.out.println("The energy needed is " + Q );
}
}
（3.9）（商业：检查ISBN-10）
package javahomework;
import java.util.Scanner;
public class java0309 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the first 9 digits of an ISBN as integer: ");
String num = input.nextLine();
String[] nums = new String [num.length()];
for (int i = 0; i < num.length();i++) {
nums[i] = num.charAt(i)+"";
}
int A = 0;
for (int i = 0; i < nums.length; i++) {
A = A + Integer.parseInt(nums[i]) * (i+1) ;
}
A = A % 11;
if (A == 10) {
System.out.println("The ISBN-10 number is " + num + "X");
}
else
System.out.println("The ISBN-10 number is " + num + A);
}
}
（3.21）（科学：某天是星期几）
package javahomework;
import java.util.Scanner;
public class java0321{
public static void main(String[] args) {
Scanner input = new Scanner (System.in);
System.out.print("Enter year:(e.g.,2012): ");
int year = input.nextInt();
System.out.print("Enter month: 1-12: ");
int month = input.nextInt();
System.out.print("Enter the day of the month: 1-31:");
int day = input.nextInt();
int q, m, j, k;
q = day;
if(month == 1) {
m = 13;
year = year -1;
}
else if(month == 2){
m = 14;
year = year -1;
}
else {
m = month;
}
j = (int)Math.floor(year/100);
k = year % 100;
int h;
h = (q + (26*(m + 1))/10 + k + k/4 + j/4 + 5*j) % 7;
switch(h) {
case(0):System.out.println("Day of the week is Saturday");break;
case(1):System.out.println("Day of the week is Sunday");break;
case(2):System.out.println("Day of the week is Monday");break;
case(3):System.out.println("Day of the week is Tuesday");break;
case(4):System.out.println("Day of the week is Wednesday");break;
case(5):System.out.println("Day of the week is Thursday");break;
case(6):System.out.println("Day of the week is Friday");break;
}
}
}
（3.23）（几何：点是否在矩形内？）
package javahomework;
import java.util.Scanner;
public class java0323 {
public static void main(String[] args) {
Scanner input = new Scanner (System.in);
System.out.print("Enter a point with two coordinates: ");
double x = input.nextDouble();
double y = input.nextDouble();
double width, height;
width = 10.0;
height = 5.0;
double x0, y0;
x0 = Math.abs(x);
y0 = Math.abs(y);
if (x0 <= width/2 && y0 <= height/2) {
System.out.println("Point " + "(" + x + "," + y +")" + "is in the rectangle " );
}
else {
System.out.println("Point " + "(" + x + "," + y +")" + "is not in the rectangle " );
}
}
}
（3.27）（几何：点是否在三角形内？）
package javahomework;
import java.util.Scanner;
public class java0327 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a point's x- and y-coordinates: ");
double x = input.nextDouble();
double y = input.nextDouble();
if (x > 0 && y > 0 && 0.5*x+y-100 < 0) {
System.out.println("Point is in the rectangle " );
}
else
System.out.println("Point is not in the rectangle " );
}
}
（4.6）（圆上的随机点）
package javahomework;
public class java0406 {
public static void main(String[] args) {
double r = 40.0;
double rs1 = Math.random() * Math.PI * 2;
double x1 = r * Math.cos(rs1);
double y1 = r * Math.sin(rs1);
double rs2 = Math.random() * Math.PI * 2;
double x2 = r * Math.cos(rs2);
double y2 = r * Math.sin(rs2);
double rs3 = Math.random() * Math.PI * 2;
double x3 = r * Math.cos(rs3);
double y3 = r * Math.sin(rs3);
double a = Math.sqrt((x2-x3)*(x2-x3) + (y2-y3)*(y2-y3));
double b = Math.sqrt((x1-x3)*(x1-x3) + (y1-y3)*(y1-y3));
double c = Math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
double A = Math.toDegrees(Math.acos((a*a - b*b -c*c) / (-2*b*c)));
double B = Math.toDegrees(Math.acos((b*b - a*a -c*c) / (-2*a*c)));
double C = Math.toDegrees(Math.acos((c*c - a*a -b*b) / (-2*a*b)));
System.out.println("The three angles are " + Math.round(A * 100) / 100.0 + " " + Math.round(B * 100) / 100.0 + " " +Math.round(C * 100) / 100.0);
}
}
（4.15）（电话键盘）
package javahomework;
import java.util.Scanner;
public class java0415 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a letter: ");
String num = input.nextLine();
if( num.equalsIgnoreCase("a") || num.equalsIgnoreCase("b") || num.equalsIgnoreCase("c")) {
System.out.println("The corresponding number is 2 ");
}
else if(num.equalsIgnoreCase("d") || num.equalsIgnoreCase("e") || num.equalsIgnoreCase("f")) {
System.out.println("The corresponding number is 3 ");
}
else if(num.equalsIgnoreCase("g") || num.equalsIgnoreCase("h") || num.equalsIgnoreCase("i")) {
System.out.println("The corresponding number is 4 ");
}
else if(num.equalsIgnoreCase("j") || num.equalsIgnoreCase("k") || num.equalsIgnoreCase("l")) {
System.out.println("The corresponding number is 5 ");
}
else if(num.equalsIgnoreCase("m") || num.equalsIgnoreCase("n") || num.equalsIgnoreCase("o")) {
System.out.println("The corresponding number is 6 ");
}
else if(num.equalsIgnoreCase("p") || num.equalsIgnoreCase("q") || num.equalsIgnoreCase("r") || num.equalsIgnoreCase("s")) {
System.out.println("The corresponding number is 7 ");
}
else if(num.equalsIgnoreCase("t") || num.equalsIgnoreCase("u") || num.equalsIgnoreCase("v")) {
System.out.println("The corresponding number is 8 ");
}
else if(num.equalsIgnoreCase("w") || num.equalsIgnoreCase("x") || num.equalsIgnoreCase("y") || num.equalsIgnoreCase("z")) {
System.out.println("The corresponding number is 9 ");
}
else
System.out.println(num + " is an invalid input ");
}
}
（4.25）（生成车牌号码）
package javahomework;
public class java0425 {
public static void main(String[] args) {
String word1_str = "";
String num1_str = "";
for(int i = 0; i < 3; i++) {
int word = (int)('A' + (int)(Math.random()*26));
char word1 = (char) word;
word1_str = word1_str + String.valueOf(word1).toString();
}
for(int i = 0; i < 4;i++) {
int number = (int)(Math.random()*10);
num1_str = num1_str + String.valueOf(number).toString();
}
System.out.println("The car's number is " + word1_str + num1_str);
}
}
（4.26）（财务应用：货币单位）
package javahomework;
import java.util.Scanner;
public class java0426 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter an amount(for example:11.56): ");
String str=input.nextLine();
if(str.indexOf('.')==-1){
if(str.equals("0")) {
System.out.println("no dollar no cent");
}
else if(str.equals("1") ) {
System.out.println(str +" dollar"+" no cent");
}
else
System.out.println(str +" dollars"+" no cent");
}
else if(str.indexOf('.')!=-1){
String dollar=str.substring(0,str.indexOf('.'));
String cent=str.substring(str.indexOf('.')+1);
if (dollar.equals("0")) {
if (cent.equals("0")) {
System.out.println("no dollar no cent");
}
else if(cent.equals("1")) {
System.out.println("no dollar "+cent+" cent");
}
else
System.out.println("no dollar "+cent+" cents");
}
else if (dollar.equals("1")) {
if (cent.equals("0")) {
System.out.println(dollar +" dollar no cent");
}
else if(cent.equals("1")) {
System.out.println(dollar +" dollar "+cent+" cent");
}
else
System.out.println(dollar +" dollar "+cent+" cents");
}
else {
if (cent.equals("0")) {
System.out.println(dollar +" dollars no cent");
}
else if(cent.equals("1")) {
System.out.println(dollar +" dollars "+cent+" cent");
}
else
System.out.println(dollar +" dollars "+cent+" cents");
}
}
}
}