第三章：选择

复习题

3.1 列出 6 个关系操作符。

解：

＞，＜，＝，＞＝，＜＝，!＝

3.2 假设 x 等于 1，给出下列布尔表达式的结果：

(x > 0)

(x < 0)

(x != 0)

(x >= 0)

(x != 1)

解：结果如下

truefalsetruetruefalse

3.3 下面涉及类型转换的变换合法吗？编写一个测试程序来验证你的结论。

boolean b = true;int i = (int)b;int i2 = 1;boolean b2 = (boolean) i2;

解：

不合法，会报错。如下图所示：

代码问题如下：

3.4 编写一个 if 语句，在 y 大于等于 0 的时候将 1 赋值给 x。

解：代码如下

public class Review3_4 {public static void main(String[] args) {int x = 0;Scanner input = new Scanner(System.in);System.out.print("输入y的值：");double y = input.nextDouble();if (y >= 0) {x = 1;}System.out.println("x的值为：" + x);}}

3.5 编写一个 if 语句，如果 score 大于 90 则增加 3% 的支付。

解：代码如下

public class Review3_5 {public static void main(String[] args) {int score;Scanner input = new Scanner(System.in);System.out.print("请输入分数：");score = input.nextInt();if (score >= 90) {double a;a = score * (1+0.03);System.out.println(a);} else {double b;b = score;}}}

3.6 编写一个 if 语句，如果 score 大于 90 则增加 3% 的支付，否则则增加 1% 的支付。

解：代码如下

public class Exercise3_6 {public static void main(String[] args) {int score;Scanner input = new Scanner(System.in);System.out.print("请输入分数：");score = input.nextInt();if (score >= 90) {double a;a = score * (1+0.03);System.out.println(a);} else {double b;b = score * (1+0.01);System.out.println(b);}}}

3.7 如果 number 是 30，a 和 b 中的代码输出是多少？如果 number 是 35 呢？

a 中代码如下：

if (number % 2 == 0)System.out.println(number + " is even.");System.out.println(number + " is odd.");

b 中代码如下：

if (number % 2 == 0)System.out.println(number + " is even.");elseSystem.out.println(number + " is odd.");

解：代码如下

public class Exercise3_7_1 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("输入 number 的值：");double number = input.nextDouble();if (number % 2 == 0)System.out.println("a - " + number + " is even.");System.out.println("a - " + number + " is odd.");if (number % 2 == 0)System.out.println("b - " + number + " is even.");elseSystem.out.println("b - " + number + " is odd.");}}

当 number 是 30，a 和 b 的输出如下：

a - 30.0 is even.a - 30.0 is odd.b - 30.0 is even.

当 number 是 35，a 和 b 的输出如下：

a - 35.0 is odd.b - 35.0 is odd.

3.8 假设 x=3 以及 y=2，如果下面代码有输出的话，请给出。如果 x=3 并且 y=4，结果是什么呢？如果 x=2 并且 y=2，结果是什么呢？绘制代码的流程图。

if (x > 2) {if (y > 2) {int z = x + y;System.out.println("z is " + z);}}elseSystem.out.println("x is " + x);

解：代码如下

public class Exercise3_8 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("请输入 x 的值：");int x = input.nextInt();System.out.print("请输入 y 的值：");int y = input.nextInt();if (x > 2) {if (y > 2) {int z = x + y;System.out.println("z is " + z);}}elseSystem.out.println("x is " + x);}}

当 x=2 以及 y = 2，没有输出。当 x=3 并且 y=4，输出如下

z is 7

当 x=2 并且 y=2，输出如下

x is 2

代码流程图如下：

3.9 假设 x=2 以及 y=3，如果下面代码有输出的话，请给出。如果 x=3 并且 y=2，结果是什么呢？如果 x=3 并且 y=3，结果是什么呢？

if (x > 2)if (y > 2) {int z = x + y;System.out.println("z is " + z);}elseSystem.out.println("x is " + x);

解：代码如下

public class Exercise3_9 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("请输入 x 的值：");int x = input.nextInt();System.out.println("请输入 y 的值：");int y = input.nextInt();if (x > 2)if (y > 2) {int z = x + y;System.out.println("z is " + z);}elseSystem.out.println("x is " + x);}}

当 x=2 以及 y = 3，没有输出。当 x=3 并且 y=2，输出如下

x is 3

当 x=3 并且 y=3，输出如下

z is 6

3.10 下面代码中有什么错误？

if (score >= 60)System.out.println("D");else if (score >= 70)System.out.println("C");else if (score >= 80)System.out.println("B");else if (score >= 90)System.out.println("A");elseSystem.out.println("F");

解：逻辑错误，代码如下

if (score >= 90) {System.out.println("A");} else if (score >= 80) {System.out.println("B");} else if (score >= 70) {System.out.println("C");} else if (score >= 60) {System.out.println("D");} else {System.out.println("F");}

3.11 以下语句哪些是等价的？哪些是合理缩进的？

解：a、c、d 是等价的；b、c 是合理缩进的。

3.12 使用布尔表达式重写以下语句。

if (count % 10 == 0)newLine = true;elsenewLine = false;

解：代码如下

boolean newLine = count % 10 == 0;

3.13 下面语句正确吗？哪个更好？

解：

语句都是正确的，语句 b 更好

3.14 如果 number 值为 14、15 或者 30，下列代码的输出是什么？

解：

number 为 14 的时候，a 输出为“14 is even”；b 输出为“14 is even”。

number 为 15 的时候，a 输出为“15 is multiple of 5”；b 输出为“15 is multiple of 5”。

number 为 30 的时候，a 输出为“30 is even”、“30 is multiple of 5”；b 输出为“30 is even”。

3.15 以下哪些是调用 Math.random() 的可能输出？

323.4、0.5、34、1.0、0.0、0.234

解：

Math.random() 返回带正号的 double 值，0.0 ≤ 返回值＜1.0。返回值是一个伪随机选择的数。

所以上边的可能输出为 0.5、0.0、0.234。

3.16

a. 如何产生一个随机的整数 i，使得 0 ≤ i＜20 ？

b. 如何产生一个随机的整数 i，使得 10 ≤ i＜20 ？

c. 如何产生一个随机的整数 i，使得 0 ≤ i ≤ 50 ？

d. 编写一个表达式，随机返回 0 或者 1。

解：代码如下

int i = (int)(Math.random()*20);int i = (int) (10+Math.random()*10);int i = (int)(Math.random()*51);int i = (int)(Math.random()+0.5);

3.17 下列两个语句等价吗？

解：

等价。

3.18 假设 x 为 1，给出下列布尔表达式的结果：

解：

falsefalsetruetruetruefalse

3.19 (a) 编写一个布尔表达式满足：若变量 num 中存储的数值在 1 到 100 之间时，表达式的值为 true。

（b）编写一个布尔表达式满足：若变量 num 中存储的数值在 1 到 100 之间，或值为负数时，表达式的值为 true。

解：代码如下

public class Review3_19 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.println("输入 num 的数值：");int num = input.nextInt();if (num >= 1 && num <= 100) {System.out.println("true");}if ((num >=1 && num <= 100) || num < 0) {System.out.println("true");}}}

3.20（a）为 |x - 5|<4.5 编写一个布尔表达式。

（b）为|x - 5|>4.5 编写一个布尔表达式。

解：

A 代码如下

Math.abs(x - 5) < 4.5

B代码如下

Math.abs(x - 5) > 4.5

3.21 假设 x 和 y 都是 int 类型，下面哪些是合法的 Java 表达式？

x > y > 0

x = y = && y

x /= y

x or y

x and y

(x != 0) || (x = 0)

解：

假设 x 为 1，y 为 2。

代码如下

public class Review3_20 {public static void main(String[] args) {int x = 1;int y = 2;x > y > 0;x = y = && y;x /= y;x or y;x and y;(x != 0) || (x = 0);}}

在编辑器中发现：

x > y > 0;

不合法。运算符 ‘>’ 不能应用于 ‘boolean’、‘int’

x = y = && y;

不合法。应为表达式

x /= y;

合法。

x or y;

不合法。不是语句

x and y;

不合法。不是语句

(x != 0) || (x = 0);

不合法。运算符 ‘||’ 不能应用于 ‘boolean’、‘int’

3.22 以下两个表达式等同吗？

解：

a 代码的意思是：既能被 2 整除也能被 3 整除的整数，即 2 和 3 的公倍数，而代码 b 的意思是：能够被 6 整除的整数。

因为 6 是 2 和 3 的最小公倍数，所以两个表达式等同。

3.23 如果 x 是 45、67 或者 101，表达式 x ≥ 50 && x ≤ 100 的值是多少？

解：

x = 45，值为 false

x = 67，值为 true

x = 101，值为 false

3.24 假设运行下面的程序时，从控制台输入的是 2 3 6，那么输出是什么？

public class Test {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("输入三个数值：");double x = input.nextDouble();double y = input.nextDouble();double z = input.nextDouble();System.out.println("(x < y && y < z) is " + (x < y && y < z));System.out.println("(x < y || y < z) is " + (x < y || y < z));System.out.println("!(x < y) is " + !(x < y));System.out.println("(x + y < z) is " + (x + y < z));System.out.println("(x + y > z) is " + (x + y > z));}}

解：输出如下

(x < y && y < z) is true(x < y || y < z) is true!(x < y) is false(x + y < z) is true(x + y > z) is false

3.25 编写布尔表达式，当年龄 age 大于 13 且小于 18 时结果为 true。

解：代码如下

if (age > 13 && age < 18) {System.out.println("true");}

3.26 编写布尔表达式，当体重 weight 大于 50 磅或者身高大于 60 英尺时结果为 true。

解：代码如下

if (weight > 50 || height > 60) {System.out.println("true");}

3.27 编写布尔表达式，当体重 weight 大于 50 磅并且身高大于 60 英尺时结果为 true。

解：代码如下

if (weight > 50 && height > 60) {System.out.println("true");}

3.28 3.26 编写布尔表达式，当体重 weight 大于 50 磅或者身高大于 60 英尺，但是，不是同时满足时结果为 true。

解：代码如下

if ((weight > 50) ^ (height > 60)) {System.out.println("true");}

3.29 switch 变量需要什么类型的数据？如果在执行完 case 语句之后没有使用关键字 break，那么下一句要执行的语句是什么？可以把 switch 语句转换成等价的 if 语句吗？或者反过来可以将 if 语句转换成等价的 switch 语句吗？使用 switch 语句的优点有哪些？

解：

switch 语句根据 char、byte、short、int 或者 String 类型的 switch 表达式来决定控制。在 switch 语句中，关键字 break 是可选的，但它通常用在每个分支的结尾，以中止执行 switch 语句的剩余部分。如果没有出现 break语句，则执行接下来的 case 语句。

3.30 执行下列 switch 语句之后，y 是多少？ 并使用 if-else 重写代码。

int x = 3;int y = 3;switch (x + 3) {case 6: y = 1;default: y += 1;}

解：switch语句的输出为“y = 2”。（因为没有使用 break 跳出，所以当 case 6 满足条件时，y = 1，没有跳出，y 继续加 1，y = 2）。

将其改为 if-else 后代码如下：

public class Exercise3_30 {public static void main(String[] args) {int x = 3;int y = 3;if ((x + 3) == 6) {y = 1;} else {y += 1;}System.out.println("y = " + y);}}

3.31 执行下列 if-else 语句之后，x 是多少？使用 switch 语句重写，并且为新的 switch 语句画出流程图。

int x = 1, a = 3;if (a == 1)x += 5;else if (a == 2)x += 10;else if (a == 3)x += 16;else if (a == 4)x += 34;

解：上边语句执行后，x = 17

switch重写语句如下：

int x = 1, a = 3;switch (a) {case 1: x += 5; break;case 2: x += 10; break;case 3: x += 16; break;case 4: x += 34; break;}

3.32 编写 switch 语句，如果 day 是 0、1、2、3、4、5、6，分别显示 Sunday、Monday、Tuesday、Tuesday、Wednesday、Thursday、Friday、Saturday。

解：代码如下

public class Exercise3_32 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter the number of day: ");int day = input.nextInt();switch (day) {case 0:System.out.println("Sunday");break;case 1:System.out.println("Monday");break;case 2:System.out.println("Tuesday");break;case 3:System.out.println("Wednesday");break;case 4:System.out.println("Thursday");break;case 5:System.out.println("Friday");break;case 6:System.out.println("Saturday");break;}}}

3.33 假设你运行下面程序的时候从控制台输入 2 3 6，将输出什么？

public class Exercise3_33 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter three numbers: ");double x = input.nextDouble();double y = input.nextDouble();double z = input.nextDouble();System.out.println((x < y && y < z) ? "sorted" : "not sorted");}}

解：输出为 sorted。

3.34 运用条件操作符重写以下 if 语句。

解：代码如下

ticketPrice = (ages >= 16) ? 20 : 10;

3.35 使用 if-else 表达式重写下面的条件表达式。

解：

(a) 表达式如下

if (x > 10) {score = 3 * scale;} else {score = 4 * scale;}

(b) 表达式如下

if(income > 10000) {tax = income * 0.2;} else {tax = income * 0.17 + 1000;}

© 表达式如下

if(number % 3 == 0) {System.out.println(i);} else {System.out.println(j);}

3.36 编写随机返回 1 或者 -1 的条件表达式。

解：

代码如下

public class Exercise3_36 {public static void main(String[] args) {int i = new Random().nextBoolean() ? 1 : -1;System.out.println(i);}}

3.37 列出布尔操作符的优先级顺序。计算下面的表达式：

true || true && falsetrue && true || false

解：

优先级顺序如下：

! (非) > ^ (异或) > && (逻辑与、条件与) > || (逻辑或、条件或)。

表达式结果如下：

true、true

3.38 除 = 之外的所有二次元操作符都是左结合的，这个说法是真还是假？

解：

这个说法是真的。所有二元运算符都是左结合的，也就是运算按从左到右的顺序执行。

3.39 计算下面的表达式：

2 * 2 - 3 > 2 && 4 - 2 > 52 * 2 - 3 > 2 || 4 - 2 > 5

解：

false、false

3.40 ( x > 0 && x < 10) 和 ((x >0) && (x < 10)) 是否一样？

((x > 0) || (x < 10)) 是否一样？

(x > 10 || x < 10 && y < 0) 和 (x > 0 || (x < 10 && y < 0)) 是否一样？

解：

三个都是一样的。

编程练习题

解：代码如下

public class Test_3_1 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter a, b, c: ");double a = input.nextDouble();double b = input.nextDouble();double c = input.nextDouble();double v = Math.pow(b, 2) - 4 * a * c;double r1,r2;if (v > 0) {r1 = ((-b) + Math.pow(v , 0.5)) / (2 * a);r2 = ((-b) - Math.pow(v , 0.5)) / (2 * a);System.out.println("The equation has two roots " + r1 + " and " + r2);} else if (v == 0) {r1 = ((-b) + Math.pow(v , 0.5)) / (2 * a);System.out.println("The equation has one root " + r1);} else {System.out.println("The equation has no real roots");}}}

解：代码如下

public class Test_3_2 {public static void main(String[] args) {int number01 = (int) System.currentTimeMillis() % 10;int number02 = (int) System.currentTimeMillis() / 7 % 10;int number03 = (int) System.currentTimeMillis() / 4 % 10;Scanner input = new Scanner(System.in);System.out.println("What is " + number01 +" + "+ number02 +" + "+ number03 +" ? ");int answer = input.nextInt();System.out.println(number01 +" + "+ number02 +" + "+ number03 + " = " + answer +" is " +(number01 + number02 + number03 == answer));}}

解：代码如下

public class Test_3_3 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter a, b, c, d, e, f: ");double a = input.nextDouble();double b = input.nextDouble();double c = input.nextDouble();double d = input.nextDouble();double e = input.nextDouble();double f = input.nextDouble();double t = a * d - b * c , x , y ;if(t != 0){x = ((e * d - b * f) / t);y = ((a * f - e * c) / t);System.out.println("x is " + x + " and " + "y is " +y);}else{System.out.println("The equation has no solution");}}}

解：代码如下

public class Test_3_4 {public static void main(String[] args) {int month = (int)(System.currentTimeMillis() % 13);switch (month){case 1 : System.out.println("The number " + month + " is " + "January"); break;case 2 : System.out.println("The number " + month + " is " + "February"); break;case 3 : System.out.println("The number " + month + " is " + "March"); break;case 4 : System.out.println("The number " + month + " is " + "April"); break;case 5 : System.out.println("The number " + month + " is " + "May"); break;case 6 : System.out.println("The number " + month + " is " + "June"); break;case 7 : System.out.println("The number " + month + " is " + "July"); break;case 8 : System.out.println("The number " + month + " is " + "August"); break;case 9 : System.out.println("The number " + month + " is " + "September"); break;case 10 : System.out.println("The number " + month + " is " + "October"); break;case 11 : System.out.println("The number " + month + " is " + "November"); break;case 12 : System.out.println("The number " + month + " is " + "December"); break;}}}

解：代码如下

public class Test_3_5 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter today's day: ");int today = input.nextInt();System.out.print("Enter the number of days elapsed since today: ");int days = input.nextInt();switch (today) {case 0 : System.out.print("Today is Sunday ");break;case 1 : System.out.print("Today is Monday ");break;case 2 : System.out.print("Today is Tuesday ");break;case 3 : System.out.print("Today is Wednesday ");break;case 4 : System.out.print("Today is Thursday ");break;case 5 : System.out.print("Today is Friday ");break;case 6 : System.out.print("Today is Saturday ");break;}days = days % 7;int future = days + today;if(future > 7){future = future - 7;}switch (future) {case 0 : System.out.println("and the future day is Sunday ");break;case 1 : System.out.println("and the future day is Monday ");break;case 2 : System.out.println("and the future day is Tuesday ");break;case 3 : System.out.println("and the future day is Wednesday ");break;case 4 : System.out.println("and the future day is Thursday ");break;case 5 : System.out.println("and the future day is Friday ");break;case 6 : System.out.println("and the future day is Saturday ");break;}}}

解：代码如下

public class Test_3_6 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter weight in pounds:");double weight = input.nextDouble();System.out.print("Enter feet:");double feet = input.nextDouble();System.out.print("Enter inches:");double inches = input.nextDouble();inches = feet * 12 + inches;final double KIL0GRAMS_PER_P0UND = 0.45359237;final double METERS_PER_INCH = 0.0254;double weightInKilograms = weight * KIL0GRAMS_PER_P0UND;double heightInMeters = inches * METERS_PER_INCH;double bmi = weightInKilograms / (heightInMeters * heightInMeters);System.out.println("BMI is " + bmi);if (bmi < 18.5)System.out.println("Underweight");else if (bmi < 25)System.out.println("Normal");else if (bmi < 30)System.out.println("Overweight");elseSystem.out.println("Obese");}}

解：代码如下

public class Test_3_7 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter an amount in double, for example 11.56: ");double amount = input.nextDouble();int remainingAmount = (int)(amount * 100);int numberOfOneDollars = remainingAmount / 100;remainingAmount = remainingAmount % 100;int numberOfQuarters = remainingAmount / 25;remainingAmount = remainingAmount % 25;int numberOfDimes = remainingAmount / 10;remainingAmount = remainingAmount % 10;int numberOfNickels = remainingAmount /5;remainingAmount =remainingAmount % 5;int numberOfPennies = remainingAmount;System.out.println("Your amount " + amount + " consists of ");if(numberOfOneDollars == 1)System.out.println("" + numberOfOneDollars + " dollar");else if (numberOfOneDollars > 1)System.out.println("" + numberOfOneDollars + " dollars");if(numberOfQuarters == 1)System.out.println("" + numberOfQuarters + " quarter");else if (numberOfQuarters > 1)System.out.println("" + numberOfQuarters + " quarters");if(numberOfDimes == 1)System.out.println("" + numberOfDimes + " dime");else if (numberOfDimes > 1)System.out.println("" + numberOfDimes + " dimes");if(numberOfNickels == 1)System.out.println("" + numberOfNickels + " nickel");else if (numberOfNickels > 1)System.out.println("" + numberOfNickels + " nickels");if(numberOfPennies == 1)System.out.println("" + numberOfPennies + " penny");else if (numberOfPennies > 1)System.out.println("" + numberOfPennies + " pennies");}}

解：代码如下

public class Test_3_8 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter a,b,c: ");int a = input.nextInt();int b = input.nextInt();int c = input.nextInt();int t;if (a > b){t = a;a = b;b = t;}if (a > c){t = a;a = c;c = t;}if (b > c){t = b;b = c;c = t;}System.out.println("The result is : " + a + " " + b + " " + c);}}

解：代码如下

public class Test_3_9 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter number: ");int d1 , d2 , d3 , d4 , d5 , d6 , d7 , d8 , d9 , retain;int number = input.nextInt();retain = number;d1 = 0;d2 = number / 10000000;number = number % 10000000;d3 = number / 1000000;number = number % 1000000;d4 = number / 100000;number = number % 100000;d5 = number / 10000;number = number % 10000;d6 = number / 1000;number = number % 1000;d7 = number / 100;number = number % 100;d8 = number / 10;number = number % 10;d9 = number;int t =(d1 * 1 + d2 * 2 + d3 * 3 + d4 * 4 + d5 * 5 + d6 * 6 + d7 * 7 + d8 * 8 + d9 * 9) % 11;if(t == 10)System.out.println("The ISBN-10 number is " + "0" + retain + "X");elseSystem.out.println("The ISBN-10 number is " + "0" + retain + t);}}

解：代码如下

public class Test_3_10 {public static void main(String args[]){int number1 = (int)(Math.random() * 10);int number2 = (int)(Math.random() * 10);System.out.print("What`s " + number1 + "+" + number2 + " ? ");Scanner input = new Scanner(System.in);int answer = input.nextInt();if (number1 + number2 == answer)System.out.println("You are correct!");else{System.out.println("You answer is wrong.");System.out.println(number1 + "+" + number2 + " should be " + (number1 + number2));}}}

解：代码如下

public class Test_3_11 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter month number 1~12: ");int month = input.nextInt();System.out.print("Enter year number: ");int year = input.nextInt();if (month == 2){if (year % 4 == 0 && year % 100 != 0 || year % 400 ==0){System.out.println("February " + year + " has 29 days");}else{System.out.println("February " + year + " has 28 days");}}else{switch (month){case 1 : System.out.println("January "+ year + " has 31 days");break;case 3 : System.out.println("March "+ year + " has 31 days");break;case 4 : System.out.println("April "+ year + " has 30 days");break;case 5 : System.out.println("May "+ year + " has 31 days");break;case 6 : System.out.println("June "+ year + " has 30 days");break;case 7 : System.out.println("July "+ year + " has 31 days");break;case 8 : System.out.println("August "+ year + " has 31 days");break;case 9 : System.out.println("September "+ year + " has 30 days");break;case 10 : System.out.println("October "+ year + " has 31 days");break;case 11 : System.out.println("November "+ year + " has 30 days");break;case 12 : System.out.println("December "+ year + " has 31 days");break;}}}}

解：代码如下

public class tt1 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter a three-digit integer: ");int number = input.nextInt();int front , later;later = number % 10;front = number / 100;if (later == front)System.out.println(number + " is a palindrome");elseSystem.out.println(number + " is not a palindrome");}}

解：代码如下

public class Test_3_13 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.println("(0-single filer, 1-married jointly or " );System.out.println("qualifying widow(er), 2-married separately, 3-head of ");System.out.print("household) Enter the filing status: ");int status = input.nextInt();System.out.print("Enter the taxable income : ");double income = input.nextDouble();double tax = 0;if (status == 0){if (income <= 8350)tax = income * 0.10;else if (income <= 33950)tax = 8350 * 0.10 + (income - 8350) * 0.15;else if (income <= 82250)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (income - 33950) * 0.25;else if (income <= 171550)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (82250 - 33950) * 0.25 + (income - 82250) * 0.28;else if (income <= 372950)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (82250 - 33950) * 0.25 + (171550 - 82250) * 0.28 + (income - 171550) * 0.33;elsetax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (82250 - 33950) * 0.25 + (171550 - 82250) * 0.28 + (372950 - 171550) * 0.33 + (income - 372950) * 0.35;}else if (status == 1){if (income <= 16700)tax = income * 0.10;else if (income <= 67900)tax = 16700 * 0.10 + (income - 16700) * 0.15;else if (income <= 137050)tax = 16700 * 0.10 + (67900 - 16700) * 0.15 + (income - 67900) * 0.25;else if (income <= 208850)tax = 16700 * 0.10 + (67900 - 16700) * 0.15 + (137050 - 67900) * 0.25 + (income - 137050) * 0.28;else if (income <= 372950)tax = 16700 * 0.10 + (67900 - 16700) * 0.15 + (137050 - 67900) * 0.25 + (208850 - 137050) * 0.28 + (income - 208850) * 0.33;elsetax = 16700 * 0.10 + (67900 - 16700) * 0.15 + (137050 - 67900) * 0.25 + (208850 - 137050) * 0.28 + (372950 - 208850) * 0.33 + (income - 372950) * 0.35;}else if (status == 2){if (income <= 8350)tax = income * 0.10;else if (income <= 33950)tax = 8350 * 0.10 + (income - 8350) * 0.15;else if (income <= 68525)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (income - 33950) * 0.25;else if (income <= 104425)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (68525 - 33950) * 0.25 + (income - 68525) * 0.28;else if (income <= 186475)tax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (68525 - 33950) * 0.25 + (104425 - 68525) * 0.28 + (income - 104425) * 0.33;elsetax = 8350 * 0.10 + (33950 - 8350) * 0.15 + (68525 - 33950) * 0.25 + (104425 - 68525) * 0.28 + (186475 - 104425) * 0.33 + (income - 186475) * 0.35;}else{if (income <= 11950)tax = income * 0.10;else if (income <= 45500)tax = 11950 * 0.10 + (income - 11950) * 0.15;else if (income <= 117450)tax = 11950 * 0.10 + (45500 - 11950) * 0.15 + (income - 45500) * 0.25;else if (income <= 190200)tax = 11950 * 0.10 + (45500 - 11950) * 0.15 + (117451 - 45500) * 0.25 + (income - 117451) * 0.28;else if (income <= 375950)tax = 11950 * 0.10 + (45500 - 11950) * 0.15 + (117451 - 45500) * 0.25 + (190200- 117451) * 0.28 + (income - 190200) * 0.33;elsetax = 11950 * 0.10 + (45500 - 11950) * 0.15 + (117451 - 45500) * 0.25 + (190200- 117451) * 0.28 + (372950 - 190200) * 0.33 + (income - 372950) * 0.35;}System.out.println("Tax is " + (int)(tax * 100) / 100.0);}}

解：代码如下

public class Test_3_14 {public static void main(String args[]){int result = (int)(Math.random() *100 % 2);Scanner input = new Scanner(System.in);System.out.print("Enter your guess: ");int guess = input.nextInt();if (guess == result)System.out.println("Your guess is right!");elseSystem.out.println("Your guess not is right!");}}

解：代码如下

public class Test_3_15 {public static void main(String args[]){int lottery = (int)(Math.random() * 1000);Scanner input = new Scanner(System.in);System.out.print("Enter your lottery (three digits): ");int guess = input.nextInt();int retain_lottery=lottery;int lotteryDigit1 = lottery / 100;lottery = lottery % 100;int lotteryDigit2 = lottery / 10;int lotteryDigit3 = lottery % 10;int guessDigit1 = guess / 100;guess = guess % 100;int guessDigit2 = guess / 10;int guessDigit3 = guess % 10;System.out.println("The lottery is " + retain_lottery);if (guess == lottery)System.out.println("Exact match: you win $10,000");else if (guessDigit1 == lotteryDigit2 && guessDigit2 == lotteryDigit3 && guessDigit3 ==lotteryDigit1)System.out.println("Exact match: you win $3,000");else if (guessDigit1 == lotteryDigit1 ||guessDigit2 == lotteryDigit2 || guessDigit3 == lotteryDigit3)System.out.println("Exact match: you win $1,000");elseSystem.out.println("Sorry,no match");}}

解：代码如下

public class Test_3_16 {public static void main(String args[]){int maxX = 50 , minX = -50;int maxY = 100 , minY = -100;Random random = new Random();int x = random.nextInt(maxX) % (maxX - minX +1) + minX;int y = random.nextInt(maxY) % (maxY - minY +1) + minY;System.out.println("( " + x + " , " + y + " )");}}

解：代码如下

public class Test_3_17 {public static void main(String args[]){int computer = (int)(Math.random() * 100 % 3);Scanner input = new Scanner(System.in);System.out.print("scissor (0), rock (1), paper (2): ");int you = input.nextInt();if(computer == you){if(computer == 0)System.out.println("The computer is rock. You are rock too. Tt is a draw ");if(computer == 1)System.out.println("The computer is scissor. You are scissor too. Tt is a draw ");if(computer == 3)System.out.println("The computer is paper. You are paper too. Tt is a draw ");}else if (computer == 0){if(you == 1)System.out.println("The computer is rock. You are scissor. You lost");if(you == 2)System.out.println("The computer is rock. You are paper. You win");}else if (computer == 1){if(you == 0)System.out.println("The computer is scissor. You are rock. You win");if(you == 2)System.out.println("The computer is scissor. You are paper. You lost");}else if (computer == 2){if(you == 0)System.out.println("The computer is paper. You are rock. You lost");if(you == 1)System.out.println("The computer is paper. You are scissor. You win");}}}

解：代码如下

public class Test_3_18 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter weight: ");int w = input.nextInt();if(w > 0 && w <=1)System.out.println("The dollar is $3.5");else if (w >1 && w <= 3)System.out.println("The dollar is $5.5");else if (w > 3 && w <= 10)System.out.println("The dollar is $8.5");else if (w > 10 && w <= 20)System.out.println("The dollar is $10.5");elseSystem.out.println("the package cannot be shipped");}}

解：代码如下

public class Test_3_19 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter three side: ");int a = input.nextInt();int b = input.nextInt();int c = input.nextInt();if((a * a + b * b) >(c * c) && (a * a + c * c) >(b * b) && (c * c + b * b) >(a * a))System.out.println("This is legal!");elseSystem.out.println("This is illegal");}}

解：代码如下

public class Test_3_20 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter the temperature in Fahrenheit between -58F and 41F :");double t = input.nextDouble();System.out.print("Enter the wind speed (>-2) in miles per hour:");double v = input.nextDouble();double Twc;if((t >= -58 && t <=41) && (v >= 2)){Twc = 35.74 + 0.6215 * t - 35.75 * Math.pow(v,0.16) + 0.4275 * t * Math.pow(v,0.16);Twc = (int)(Twc * 100000);Twc = Twc / 100000;System.out.println("The wind chill index is " + Twc);}elseSystem.out.println("The open temperature or wind speed is illegal");}}

解：代码如下

public class Test_3_21 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter year:(e.g., ):");int year = input.nextInt();System.out.print("Enter month: 1-12:");int m = input.nextInt();if (m == 1){m = 13;year = year -1;}if (m == 2) {m = 14;year = year -1;}System.out.print("Enter the day of the month: 1-31:");int q = input.nextInt();int j = year / 100;int k = year % 100;int 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;}}}

解：代码如下

public class Test_3_22 {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 x0 = 0.0 , y0 = 0.0 ;double length = Math.pow(Math.pow(x - x0 , 2) + Math.pow(y - y0 , 2), 0.5);if (length <= 10.0)System.out.println("Point (" + x + " , " + y + ") is in the circle");elseSystem.out.println("Point (" + x + " , " + y + ") is not in the circle");}}

解：代码如下

public class Test_3_23 {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();if (x <= 10.0 / 2 && x >= -(10.0 /2) && y <= 5.0 / 2 && y >= -(5.0 / 2))System.out.println("Point (" + x + " , " + y + ") is in the rectangle");elseSystem.out.println("Point (" + x + " , " + y + ") is not in the rectangle");}}

解：代码如下

public class Test_3_24 {public static void main(String args[]){int number = (int)(Math.random() * 13 + 1);int flower = (int)(Math.random() * 4 + 1);System.out.print("The card you pick is ");switch (number){case 1 : System.out.print("Ace ");break;case 2 : System.out.print("2 ");break;case 3 : System.out.print("3 ");break;case 4 : System.out.print("4 ");break;case 5 : System.out.print("5 ");break;case 6 : System.out.print("6 ");break;case 7 : System.out.print("7 ");break;case 8 : System.out.print("8 ");break;case 9 : System.out.print("9 ");break;case 10 : System.out.print("10 ");break;case 11 : System.out.print("Jack ");break;case 12 : System.out.print("Queen ");break;case 13 : System.out.print("King ");break;}switch (flower){case 1 : System.out.print(" of Clubs");break;case 2 : System.out.print(" of Diamonds");break;case 3 : System.out.print(" of Hearts");break;case 4 : System.out.print(" of Spades");break;}}}

解：代码如下

public class Test_3_25 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter x1, y1, x2, y2, x3, y3, x4, y4:");double x1 = input.nextDouble();double y1 = input.nextDouble();double x2 = input.nextDouble();double y2 = input.nextDouble();double x3 = input.nextDouble();double y3 = input.nextDouble();double x4 = input.nextDouble();double y4 = input.nextDouble();double t = (y1-y2)*(x4-x3)-(y3-y4)*(x2-x1);if ( t != 0 ){double x = (((y1-y2)*x1-(x1-x2)*y1)*(x4-x3) - (x2-x1)*((y3-y4)*x3-(x3-x4)*y3)) / t;double y = (((y3-y4)*x3-(x3-x4)*y3)*(y1-y2) - (y3-y4)*((y1-y2)*x1-(x1-x2)*y1)) / t;System.out.println("The intersecting point is at ( " + x + " , " + y + " )");}elseSystem.out.println("The two lines are parallel");}}

解：代码如下

public class Test_3_26 {public static void main(String args[]){Scanner input = new Scanner(System.in);System.out.print("Enter an integer: ");int number = input.nextInt();System.out.print("Is 10 divisible by 5 and 6? ");if(number / 6 == 1 && number / 5 == 1)System.out.println("true");elseSystem.out.println("false");System.out.print("Is 10 divisible by 5 or 6? ");if(number / 6 == 1 || number / 5 == 1)System.out.println("true");elseSystem.out.println("false");System.out.print("Is 10 divisible by 5 or 6，but not both? ");if((number / 6 == 1 && number / 5 != 1) || (number / 6 !=1 && number / 5 ==1))System.out.println("true");elseSystem.out.println("false");}}

解：代码如下

public class Test_3_27 {public static void main(String[] args) {double xCoordinate, yCoordinate;System.out.print("Enter a point's x- and y-coordinates: ");Scanner input = new Scanner(System.in);xCoordinate = input.nextDouble();yCoordinate = input.nextDouble();double a = (200 - xCoordinate) / 200 * 100;double b = (100 - yCoordinate) / 100 * 200;// 验证坐标是否在三角形中System.out.println(xCoordinate <= b && yCoordinate <= a? "The point is in the triangle!" : "The point is not in the triangle!");}}

解：代码如下

public class Test_3_28 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("Enter r1's center x-,y-cooordinates, width,and height: ");double x1 = input.nextDouble();double y1 = input.nextDouble();double w1 = input.nextDouble();double h1 = input.nextDouble();System.out.print("Enter r2's center x-,y-coordinates, width,and height:");double x2 = input.nextDouble();double y2 = input.nextDouble();double w2 = input.nextDouble();double h2 = input.nextDouble();double xDistance = x1 - x2 >= 0 ? x1-x2 : x2-x1;double yDistance = y1 - y2 >= 0 ? y1-y2 : y2-y1;if (xDistance <= (w1 - w2) / 2 && yDistance <= (h1 - h2) / 2)System.out.println("r2 is inside r1");else if (xDistance <= (w1 + w2) / 2 && yDistance <= (h1 + h2) / 2)System.out.println("r2 overlaps r1");else System.out.println("r2 does not overlap r1");}}

解：代码如下

public class Test_3_29 {public static void main(String[] args) {double xCoordinateCircle1, yCoordinateCircle1, radiusCircle1;double xCoordinateCircle2, yCoordinateCircle2, radiusCircle2;double distanceFromP1ToP2;System.out.print("Enter circle1's center x-,y-coordinates,and radius: ");Scanner input = new Scanner(System.in);xCoordinateCircle1 = input.nextDouble();yCoordinateCircle1 = input.nextDouble();radiusCircle1 = input.nextDouble();System.out.print("Enter circle2's center x-,y-coordinates,and radius: ");xCoordinateCircle2 = input.nextDouble();yCoordinateCircle2 = input.nextDouble();radiusCircle2 = input.nextDouble();distanceFromP1ToP2 = Math.pow((Math.pow(xCoordinateCircle1-xCoordinateCircle2, 2)+ Math.pow(yCoordinateCircle1-yCoordinateCircle2, 2)), 0.5);if(radiusCircle1 + radiusCircle2 >= distanceFromP1ToP2) {if(radiusCircle1 - radiusCircle2 >= distanceFromP1ToP2)System.out.println("circle2 is inside circle1");elseSystem.out.println("circle2 overlaps circle1");}elseSystem.out.println("circle2 does not overlap circle1");input.close();}}

解：代码如下

public class Test_3_30 {public static void main(String[] args) {int ZoneOffset;long CurrHours, CurrMinutes, CurrSeconds;long CurrentMilliSeconds;CurrentMilliSeconds = System.currentTimeMillis();CurrSeconds = CurrentMilliSeconds / 1000 % 60;CurrMinutes = CurrentMilliSeconds / 1000 / 60 % 60;CurrHours = CurrentMilliSeconds / 1000 / 60 / 60 % 24;System.out.print("Enter the time zone offset to GMT : ");Scanner ZoneOffsetInput = new Scanner(System.in);ZoneOffset = ZoneOffsetInput.nextInt();CurrHours = (CurrHours + ZoneOffset + 24) % 24;if(CurrHours <= 12)System.out.println("The current time is "+ CurrHours + ":" + CurrMinutes + ":" + CurrSeconds + " AM");else{CurrHours %= 12;System.out.println("The current time is "+ CurrHours + ":" + CurrMinutes + ":" + CurrSeconds + " PM");}ZoneOffsetInput.close();}}

解：代码如下

public class Test_3_31 {public static void main(String[] args) {double exchangeRate, moneyAmount, exchangedAmount;final int exchangeMode;System.out.print("Enter the exchange rate from dollars to RMB: ");Scanner input = new Scanner(System.in);exchangeRate = input.nextDouble();System.out.print("Enter 0 to convert dollars to RMB and 1 vice versa: ");exchangeMode = input.nextInt();if(exchangeMode == 0){System.out.print("Enter the dollar amount: ");moneyAmount = input.nextDouble();exchangedAmount = moneyAmount * exchangeRate;System.out.println("$" + moneyAmount + " is " + exchangedAmount + " yuan");}else if(exchangeMode == 1){System.out.print("Enter the RMB amount: ");moneyAmount = input.nextDouble();exchangedAmount = moneyAmount / exchangeRate;System.out.println(moneyAmount + " yuan is $" + exchangedAmount);}elseSystem.out.println("Incorrect input");input.close();}}

解：代码如下

public class Test_3_32 {public static void main(String[] args) {double xP0, yP0, xP1, yP1, xP2, yP2;int discriminant;// Prompt the user to enter the three pointsScanner input = new Scanner(System.in);System.out.print("Enter three points for p0, p1, and p2: ");xP0 = input.nextDouble();yP0 = input.nextDouble();xP1 = input.nextDouble();yP1 = input.nextDouble();xP2 = input.nextDouble();yP2 = input.nextDouble();discriminant = (int)((xP1 - xP0) * (yP2 - yP0) - (xP2 - xP0) * (yP1 - yP0));if(discriminant > 0)System.out.println("p2 is on the left side of the line");else if(0 == discriminant)System.out.println("p2 is on the same line");elseSystem.out.println("p2 is on the right side of the line");input.close();}}

解：代码如下

public class Test_3_33 {public static void main(String[] args) {double weightPackage1,pricePackage1;double weightPackage2,pricePackage2;Scanner input = new Scanner(System.in);System.out.print("Enter weight and price for package 1: ");weightPackage1 = input.nextDouble();pricePackage1 = input.nextDouble();System.out.print("Enter weight and price for package 2: ");weightPackage2 = input.nextDouble();pricePackage2 = input.nextDouble();if(pricePackage1 / weightPackage1 < pricePackage2 / weightPackage2)System.out.println("Package 1 has a better price.");else if(pricePackage1 / weightPackage1 > pricePackage2 / weightPackage2)System.out.println("Package 2 has a better price.");elseSystem.out.println("Two packages have the same price.");input.close();}}

解：代码如下

public class Test_3_34 {public static void main(String[] args) {double xP0, yP0, xP1, yP1, xP2, yP2;int discriminant;Scanner input = new Scanner(System.in);// Prompt the user to enter the three pointsSystem.out.print("Enter three points for p0, p1, and p2: ");xP0 = input.nextDouble();yP0 = input.nextDouble();xP1 = input.nextDouble();yP1 = input.nextDouble();xP2 = input.nextDouble();yP2 = input.nextDouble();discriminant = (int)((xP1 - xP0) * (yP2 - yP0) - (xP2 - xP0) * (yP1 - yP0));if(0 == discriminant && xP2 <= (xP0 > xP1?xP0:xP1) && xP2 >= (xP0 > xP1?xP1:xP0))System.out.println("(" + xP2 + ", " + yP2 + ") is on the line segment from"+ " (" + xP0 + ", " + yP0 + ") to "+ "(" + xP1 + ", " + yP1 + ")" );elseSystem.out.println("(" + xP2 + ", " + yP2 + ") is not on the line segment from"+ " (" + xP0 + ", " + yP0 + ") to "+ "(" + xP1 + ", " + yP1 + ")" );input.close();}}