04-數(shù)學函數(shù)、字符和字符串
-
4.1 引言
- 介紹數(shù)學函數(shù)棺蛛、字符和字符串對象怔蚌，并使用他們來開發(fā)程序。
-
4.2 常用數(shù)學函數(shù)
- 4.2.1 三角函數(shù)方法
<center>Math類中的三角函數(shù)方法</center>
方法 描述 sin(radians) 返回以弧度為單位的角度的三角正弦函數(shù)值 cos(radians) 返回以弧度為單位的角度的三角余弦函數(shù)值 tan(radians) 返回以弧度為單位的角度的三角正切函數(shù)值 toRadians(degrees) 將以度為單位的角度值轉(zhuǎn)換為以弧度表示 toDegrees(radians) 將以弧度為單位的角度值轉(zhuǎn)換為以度表示 asin(a) 返回以弧度為單位的角度的反三角正弦函數(shù)值 acos(a) 返回以弧度為單位的角度的反三角余弦函數(shù)值 atan(a) 返回以弧度為單位的角度的反三角正切函數(shù)值 package chapter04; public class MathMethod { public static void main(String[] args){ System.out.println(Math.toDegrees(Math.PI)); System.out.println(Math.toRadians(30)); System.out.println(Math.sin(0)); System.out.println(Math.sin(Math.toRadians(270))); System.out.println(Math.sin(Math.PI / 6)); System.out.println(Math.sin(Math.PI / 2)); System.out.println(Math.cos(0)); System.out.println(Math.cos(Math.PI / 6)); System.out.println(Math.cos(Math.PI / 2)); System.out.println(Math.asin(0.5)); System.out.println(Math.acos(0.5)); System.out.println(Math.atan(1.0)); } }結(jié)果顯示：
180.0 0.5235987755982988 0.0 -1.0 0.49999999999999994 1.0 1.0 0.8660254037844387 6.123233995736766E-17 0.5235987755982989 1.0471975511965979 0.7853981633974483 Process finished with exit code 0- 4.2.2 指數(shù)函數(shù)方法
<center>Math類中的指數(shù)函數(shù)方法</center>
| 方法 |描述 |
|--|--|
|exp(x) |返回e的x次方（e^x） |
| log(x) | 返回x的自然對數(shù)（Inx=loge（x） |
| log10(x)| 返回x的以10為底的對數(shù)（log10（x））|
| pow(a,b) |返回a的b次方（a^b） |
| sqrt(x) | 對于x≥0的數(shù)字鞠值，返回x的平方根|
package chapter04; public class MathMethod { public static void main(String[] args){ System.out.println(Math.exp(3.5)); System.out.println(Math.log(3.5)); System.out.println(Math.log10(3.5)); System.out.println(Math.pow(2,3)); System.out.println(Math.pow(3,2)); System.out.println(Math.pow(4.5,2.5)); System.out.println(Math.sqrt(4)); System.out.println(Math.sqrt(10.5)); } }結(jié)果顯示：
33.11545195869231 1.252762968495368 0.5440680443502757 8.0 9.0 42.95673695708276 2.0 3.24037034920393 Process finished with exit code 0- 4.2.3 取整方法
<center>Math類中的取整方法</center>
| 方法 |描述 |
|--|--|
| ceil(x) | x向上取整為它最近的整數(shù)媚创。該整數(shù)作為一個雙精度值返回 |
| floor(x)| x向下取整為它最近的整數(shù)。該整數(shù)作為一個雙精度值返回|
| rint(x)| x取整為它最接近的整數(shù)彤恶。如果x與兩個整數(shù)的距離相等钞钙，偶數(shù)的整數(shù)作為一個雙精度值返回 |
| round(x)| 如果x是單精度數(shù)，返回（int）Math.floor(x+0.5)声离；如果x是雙精度數(shù)芒炼，返回（long）Math.floor(x+0.5)|
package chapter04; public class MathMethod { public static void main(String[] args){ System.out.println(Math.ceil(2.1)); System.out.println(Math.ceil(2.0)); System.out.println(Math.ceil(-2.0)); System.out.println(Math.ceil(-2.1)); System.out.println(Math.floor(2.1)); System.out.println(Math.floor(2.0)); System.out.println(Math.floor(-2.0)); System.out.println(Math.floor(-2.1)); System.out.println(Math.rint(2.1)); System.out.println(Math.rint(-2.0)); System.out.println(Math.rint(-2.1)); System.out.println(Math.rint(2.5)); System.out.println(Math.rint(4.5)); System.out.println(Math.rint(-2.5)); System.out.println(Math.round(2.6f));//return int System.out.println(Math.round(2.0));//return long System.out.println(Math.round(-2.0f));//returns int System.out.println(Math.round(-2.6));//return long System.out.println(Math.round(-2.4));//return long } }結(jié)果顯示：
3.0 2.0 -2.0 -2.0 2.0 2.0 -2.0 -3.0 2.0 -2.0 -2.0 2.0 4.0 -2.0 3 2 -2 -3 -2 Process finished with exit code 0- 4.2.4 min、max和abs方法
- min和max方法用于返回兩個數(shù)（int术徊、long本刽、float和double型）的最小值和最大值。
- abs函數(shù)以返回一個數(shù)（int、long子寓、float和double）的絕對值暗挑。
- 4.2.1 三角函數(shù)方法
```java
package chapter04;
public class MathMethod {
public static void main(String[] args){
System.out.println(Math.max(2,3));
System.out.println(Math.min(2.5,4.6));
System.out.println(Math.max(Math.max(2.5,4.6),Math.min(3,5.6)));
System.out.println(Math.abs(-2));
System.out.println(Math.abs(-2.1));
}
}
```
結(jié)果顯示：
```java
3
2.5
4.6
2
2.1
Process finished with exit code 0
```
- 4.2.5 random方法
- random（）方法生成大于等于0.0且小于1.0的double型隨機數(shù)。
```java
(int)(Math.random() * 10);//返回0-9之前的一個隨機整數(shù)
50 + (int)(Math.random() * 50);//返回50-99之間的一個隨機數(shù)
a + Math.random() * b;//返回a——a+b之間的一個隨機數(shù)斜友，不包括a+b
```
- 4.2.6 示例學習：計算三角形的角度
- 提示用戶輸入三角形三個頂點的x和y坐標值炸裆，然后顯示三個角。
```java
package chapter04;
import java.util.Scanner;
public class ComputeAngles {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("Enter three points: ");
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 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 - b * b - a * a) / (-2 * b * a)));
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);
}
}
```
- 4.3 字符數(shù)據(jù)類型和操作
- 4.3.1 Unicode和ASCII碼
- 字符數(shù)據(jù)類型用于表示單個字符鲜屏。
- 字符串字面值必須括在雙引號中烹看。而字符字面值是括在單引號中的單個字符。因為“A”是一個字符串洛史，而‘A’是一個字符惯殊。
- 自增和自減操作符也可用在char型變量上，這會得到該字符之前或之后的Unicode字符也殖。例如土思，下面的語句顯示字符b：
- 4.3.1 Unicode和ASCII碼
```java
char ch = 'a';
System.out.println(++ch);
```
- 4.3.2 特殊字符的轉(zhuǎn)義序列
- 反斜杠\被稱為轉(zhuǎn)義字符。它是一個特殊字符毕源。
- 4.3.3 字符型數(shù)據(jù)與數(shù)字型數(shù)據(jù)之間的轉(zhuǎn)換
- char型數(shù)據(jù)可以轉(zhuǎn)換成任意一種數(shù)值類型浪漠，反之亦然。將整數(shù)轉(zhuǎn)換成char型數(shù)據(jù)時霎褐，只用到該數(shù)據(jù)的低十六位址愿，其余部分都被忽略。
```java
package chapter04;
public class MathMethod {
public static void main(String[] args){
char ch1 = (char)0XAB0041;
System.out.println(ch1);
char ch2 = (char)65.25;
System.out.println(ch2);
int i = (int)'A';
System.out.println(i);
byte b = 'a';
int j = 'a';
byte bb = (byte)'\uFFF4';
int z = '2' + '3';
System.out.println("z is " + z);
int x = 2 + 'a';
System.out.println("x is " + x);
System.out.println(x + " is the Unicode for character " + (char)x);
System.out.println("Chapter " + '2');
}
}
```
結(jié)果顯示：
```java
A
A
65
z is 101
x is 99
99 is the Unicode for characterc
Chapter 2
Process finished with exit code 0
```
- 4.3.4 字符比較和測試
- 兩個字符可以使用關(guān)系操作符進行比較冻璃，如同比較兩個數(shù)字一樣响谓。
```java
package chapter04;
public class CharacterMethod {
public static void main(String[] args){
System.out.println("isDidit('a') is " + Character.isDigit('a'));
System.out.println("isLetter('a') is " + Character.isLetter('a'));
System.out.println("isLowerCase('a') is " + Character.isLowerCase('a'));
System.out.println("isUpperCase('a') is " + Character.isUpperCase('a'));
System.out.println("toLowerCase('T') is " + Character.toLowerCase('T'));
System.out.println("toUpperCase('q') is " + Character.toUpperCase('q'));
}
}
```
-
4.4 String類型
字符串是一個字符序列。String類型不是基本類型省艳，而是引用類型娘纷。
在這里插入圖片描述- 4.4.1 獲取字符串長度
- 可以調(diào)用字符串的length（）方法獲取他的長度。
- 為方便起見跋炕，Java允許在不創(chuàng)建新變量的情況下赖晶，使用字符串字面值直接飲用字符串。這樣“Welcome to Java”.length()是正確的辐烂，它返回15.注意遏插，“”表示空字符串，并且.length()為0纠修。
- 4.4.2 從字符串中獲取字符
- 方法s.charAt(index)可用于提取字符串s中的某個特定字符胳嘲。
- 在字符串s中越界訪問字符是一個常見的程序設(shè)計錯誤矫渔。為了避免此類錯誤颊亮，要確保使用的下標不會超過s.length()-1犀勒。
- 4.4.3 連接字符串
- 加號（+）也可以用于連接字符串和數(shù)組统舀。在這種情況下揩悄，先將數(shù)字轉(zhuǎn)換成字符串蝗岖，然后再進行連接碉输。i跟继，若要用加號實現(xiàn)連接的功能，至少要有一個操作數(shù)必須為字符串福荸。
- 4.4.4 字符串的轉(zhuǎn)換
- 方法trim（）通過刪除字符串兩端的空白字符返回一個新字符串蕴坪。字符‘ ’、\t敬锐、\f、\r或者\n被稱為空白字符呆瞻。
- 4.4.5 從控制臺讀取字符串
- 將使用方法next()台夺、nextByte()、nextShort()痴脾、nextInt()颤介、nextLong()、nextFloat()和nextDouble()的輸入稱為基于標記的輸入赞赖，因為他們讀取采用空白字符分隔的單個元素滚朵，而不是讀取整行。nextLine()方法稱為基于行的輸入前域。
- 4.4.6 從控制臺讀取字符
- 調(diào)用nextLine()方法讀取一個字符串辕近，然后在字符串上調(diào)用charAt(0)來返回一個字符。
-
4.4.7 字符串比較
在這里插入圖片描述package chapter04; import java.util.Scanner; public class OrderTwoCities { public static void main(String[] args){ Scanner input = new Scanner(System.in); System.out.print("Enter the first city: "); String city1 = input.nextLine(); System.out.print("Enter the second city: "); String city2 = input.nextLine(); if (city1.compareTo(city2) < 0) System.out.println("The cities in alphabetical order are " + city1 + " " + city2); else System.out.println("The cities in alphabetical order are " + city2 + " " + city1); } } -
4.4.8 獲得子字符串
在這里插入圖片描述- 如果beginIndex為endIndex匿垄，substring(beginIndex,endIndex)返回一個長度為0的空字符串移宅。如果beginIndex>endIndex，將發(fā)生運行錯誤椿疗。
-
4.4.9 獲取字符串中的字符或者子串
在這里插入圖片描述 - 4.4.10 字符串和數(shù)字間的轉(zhuǎn)換
- 4.4.1 獲取字符串長度
```java
package chapter04;
public class StringToInteger {
public static void main(String[] args){
String intString = "123";
int intValue = Integer.parseInt(intString);
System.out.println(intValue);
String doubleString = "3.1415926";
double doubleValue = Double.parseDouble(doubleString);
System.out.println(doubleValue);
int number = 222;
String s = number + "";
System.out.println(s);
}
}
```
- 4.5 示例學習
-
4.5.1 猜測生日
在這里插入圖片描述package chapter04; import java.util.Scanner; public class GuessBirthday { public static void main(String[] args){ String set1 = "1 3 5 7\n" + "9 11 13 15\n" + "17 19 21 23\n" + "25 27 29 31"; String set2 = "2 3 6 7\n" + "10 11 14 15\n" + "18 19 22 23\n" + "26 27 30 31"; String set3 = "4 5 6 7\n" + "12 13 14 15\n" + "20 21 22 23\n" + "28 29 30 31"; String set4 = "8 9 10 11\n" + "12 13 14 15\n" + "24 25 26 27\n" + "28 29 30 31"; String set5 = "16 17 18 19\n" + "20 21 22 23\n" + "24 25 26 27\n" + "28 29 30 31"; int day = 0; Scanner input = new Scanner(System.in); System.out.print("Is you birthday in Set1?\n"); System.out.print(set1); System.out.print("\nEnter 0 for No and 1 for Yes: "); int answer = input.nextInt(); if (answer == 1) day += 1; System.out.print("\nIs you birthday in Set2?\n"); System.out.print(set2); System.out.print("\nEnter 0 for No and 1 for Yes: "); answer = input.nextInt(); if (answer == 1) day += 2; System.out.print("\nIs you birthday in Set3?\n"); System.out.print(set3); System.out.print("\nEnter 0 for No and 1 for Yes: "); answer = input.nextInt(); if (answer == 1) day += 4; System.out.print("\nIs you birthday in Set4?\n"); System.out.print(set4); System.out.print("\nEnter 0 for No and 1 for Yes: "); answer = input.nextInt(); if (answer == 1) day += 8; System.out.print("\nIs you birthday in Set5?\n"); System.out.print(set5); System.out.print("\nEnter 0 for No and 1 for Yes: "); answer = input.nextInt(); if (answer == 1) day += 16; System.out.println("\nYour birthday is " + day + "!"); } }在這里插入圖片描述 4.5.2 將十六進制數(shù)轉(zhuǎn)換為十進制
-
```java
package chapter04;
import java.util.Scanner;
public class HexDigit2Dec {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("Enter a hex digit: ");
String hexString = input.nextLine();
if (hexString.length() != 1){
System.out.println("You must enter exactly one character");
System.exit(1);
}
char ch = Character.toUpperCase(hexString.charAt(0));
if ('A' <= ch && ch <= 'F'){
int value = ch - 'A' + 10;
System.out.println("The decimal value for hex digit " + ch + " is " + value);
}
else if (Character.isDigit(ch)){
System.out.println("The decimal value for hex digit " + ch + " is " + ch);
}
else{
System.out.println(ch + " is an invalid input");
}
}
}
```
- 4.5.3 使用字符串修改彩票程序
```java
package chapter04;
import java.util.Scanner;
public class LotteryUsingStrings {
public static void main(String[] args){
String lottery = "" + (int)(Math.random() * 10) + (int)(Math.random() * 10);
Scanner input = new Scanner(System.in);
System.out.print("Enter your lottery pick (two digits): ");
String guess = input.nextLine();
char lotteryDigit1 = lottery.charAt(0);
char lotteryDigit2 = lottery.charAt(1);
char guessDigit1 = guess.charAt(0);
char guessDigit2 = guess.charAt(1);
System.out.println("The lottery number is " + lottery);
if (guess.equals(lottery))
System.out.println("Exact match:you win $10,000");
else if (guessDigit2 == lotteryDigit1 && guessDigit1 == lotteryDigit2)
System.out.println("Match all digits:you win $3,000");
else if (guessDigit1 == lotteryDigit1 || guessDigit1 == lotteryDigit2 || guessDigit2 == lotteryDigit2 || guessDigit2 == lotteryDigit1)
System.out.println("Match one digit:yuo win $1,000");
else
System.out.println("Sorry,no match");
}
}
```
- 4.6 格式化控制臺輸出
- 可以使用System.out.printf方法在控制臺上顯示格式化輸出漏峰。
- printf中的f代表格式（format），暗示著方法將以某種格式打印届榄。調(diào)用這個方法的語法是：
```java
System.out.printf(format,item1,item2,...,itemk);
```
[圖片上傳失敗...(image-edf74e-1601915130907)]
在這里插入圖片描述
- 如果項需要比指定寬度更多的空間浅乔，寬度自動增加。例如铝条，下面的代碼：
```java
System.out.printf("%3d#%2s#%4.2f\n",1234,"Java",51.6653);
```
結(jié)果顯示：
```java
1234#Java#51.67
```
- 如果要顯示一個帶有逗號的數(shù)字靖苇，可以在數(shù)字限定符前面添加一個逗號。
```java
System.out.printf("%,8d %,10.1f\n",12345678,12345678.263);
```
結(jié)果顯示：
```java
12,345,678 12,345,678.3
```
- 如果要在數(shù)字前面添加0而不是空格來湊齊位數(shù)攻晒，可以在一個數(shù)字限定符前面添加0顾复。
```java
System.out.printf("%08d %08.1f\n",1234,5.63);
```
結(jié)果顯示：
```java
00001234 000005.6
```
- 默認情況下，輸出是右對齊的鲁捏⌒驹遥可以在格式限定符中放一個減號(-)萧芙，指定該項在指定域中的出書是左對齊的。
```java
System.out.printf("%-8d%-8s%-8.1f\n",1234,"Java",5.63);
```
結(jié)果顯示：
```java
1234 Java 5.6
```
- 條目與格式標識符必須在類型上嚴格匹配假丧。對應于格式標識符%f或%e的條目必須是浮點型值双揪，可以使用%.2f來指定一個小數(shù)點后兩位的浮點數(shù)值，而是用%0.2f是不正確 包帚。
package chapter04;
public class FormatDemo {
public static void main(String[] args){
System.out.printf("%-10s%-10s%-10s%-10s%-10s\n","Degrees","Radians","Sine","Cosine","Tangent");
int degrees = 30;
double radians = Math.toRadians(degrees);
System.out.printf("%-10d%-10.4f%-10.4f%-10.4f%-10.4f\n",degrees,radians,Math.sin(radians),Math.cos(radians),Math.tan(radians));
degrees = 60;
radians = Math.toRadians(degrees);
System.out.printf("%-10d%-10.4f%-10.4f%-10.4f%-10.4f\n",degrees,radians,Math.sin(radians),Math.cos(radians),Math.tan(radians));
}
}
結(jié)果顯示：
Degrees Radians Sine Cosine Tangent
30 0.5236 0.5000 0.8660 0.5774
60 1.0472 0.8660 0.5000 1.7321
Process finished with exit code 0
- 編程小習題
-
1渔期、在這里插入圖片描述
package chapter04; import java.util.Scanner; public class Code_01 { public static void main(String[] args){ Scanner input = new Scanner(System.in); System.out.print("Enter the length from the center to a vertex: "); double r = input.nextDouble(); double s = 2 * r * Math.sin(Math.PI / 5); double area = 5 * s * s / (4 * Math.tan(Math.PI / 5)); System.out.printf("The area of the pentagon is %.2f",area); } } -
2、在這里插入圖片描述
package chapter04; public class Code_06 { public static void main(String[] args){ double x1, y1, x2, y2, x3, y3; double angleA,angleB,angleC,alpha; double a,b,c; alpha = Math.random() * (2 * Math.PI); x1 = 40 * Math.cos(alpha); y1 = 40 * Math.sin(alpha); alpha = Math.random() * (2 * Math.PI); x2 = 40 * Math.cos(alpha); y2 = 40 * Math.sin(alpha); alpha = Math.random() * (2 * Math.PI); x3 = 40 * Math.cos(alpha); y3 = 40 * Math.sin(alpha); a = Math.sqrt(Math.pow(x1 - x2, 2)+Math.pow(y1 - y2, 2)); b = Math.sqrt(Math.pow(x1 - x3, 2)+Math.pow(y1 - y3, 2)); c = Math.sqrt(Math.pow(x3 - x2, 2)+Math.pow(y3 - y2, 2)); angleA = Math.toDegrees(Math.acos((a * a - b * b - c * c) / (-2 * b * c))); angleB = Math.toDegrees(Math.acos((b * b - a * a - c * c) / (-2 * a * c))); angleC = Math.toDegrees(Math.acos((c * c - b * b - a * a) / (-2 * b * a))); System.out.printf("The first angle in degree is %.2f\n", angleA); System.out.printf("The second angle in degree is %.2f\n", angleB); System.out.printf("The third angle in degree is %.2f", angleC); } } - 3渴邦、[圖片上傳失敗...(image-75be4e-1601915130907)]
package chapter04; import java.util.Scanner; public class Code_08 { public static void main(String[] args){ Scanner input = new Scanner(System.in); System.out.print("Enter an ASCII code : "); int number = input.nextInt(); System.out.println("The character for ASCII code " + number + " is " + (char)number); } } - 4疯趟、[圖片上傳失敗...(image-30ecef-1601915130907)]
package chapter04; import java.util.Scanner; public class Code_09 { public static void main(String[] args){ Scanner input = new Scanner(System.in); System.out.print("Enter a character: "); String str = input.nextLine(); char character = str.charAt(0); System.out.println("The Unicode for the character " + character + " is " + (int)character); } } -
5、在這里插入圖片描述
package chapter04; import java.util.Scanner; public class Code_15 { public static void main(String[] args){ Scanner input = new Scanner(System.in); System.out.print("Enter a letter: "); String str = input.nextLine(); char letter = str.toUpperCase().charAt(0); if (letter == 'A' || letter == 'B' || letter == 'C') System.out.println("The corresponding number is 2"); else if (letter == 'D' || letter == 'E' || letter == 'F') System.out.println("The corresponding number is 3"); else if (letter == 'G' || letter == 'H' || letter == 'I') System.out.println("The corresponding number is 4"); else if (letter == 'J' || letter == 'K' || letter == 'L') System.out.println("The corresponding number is 5"); else if (letter == 'M' || letter == 'N' || letter == 'O') System.out.println("The corresponding number is 6"); else if (letter == 'P' || letter == 'Q' || letter == 'R' || letter == 'S') System.out.println("The corresponding number is 7"); else if (letter == 'T' || letter == 'U' || letter == 'V') System.out.println("The corresponding number is 8"); else System.out.println("The corresponding number is 9"); } } - 6谋梭、[圖片上傳失敗...(image-f286eb-1601915130907)]
package chapter04; public class Code_16 { public static void main(String [] args){ System.out.println((char) ((int)(Math.random() * 26) + 65)); } } -
7信峻、在這里插入圖片描述
package chapter04; import java.util.*; public class Code_21 { public static void main(String[] args){ String ssnString; System.out.print("Enter a SSN: "); Scanner input = new Scanner(System.in); ssnString = input.nextLine(); if(ssnString.length() == 11) { if(Character.isDigit(ssnString.charAt(0)) && Character.isDigit(ssnString.charAt(1)) && Character.isDigit(ssnString.charAt(2)) && ssnString.charAt(3) == '-' && Character.isDigit(ssnString.charAt(4)) && Character.isDigit(ssnString.charAt(5)) && ssnString.charAt(6) == '-' && Character.isDigit(ssnString.charAt(7)) && Character.isDigit(ssnString.charAt(8)) && Character.isDigit(ssnString.charAt(9)) && Character.isDigit(ssnString.charAt(10))) System.out.println(ssnString + " is a valid social security number"); else System.out.println(ssnString + " is an invalid social security number"); } else System.out.println(ssnString + " is an invalid social security number"); input.close(); } } -
8、在這里插入圖片描述
package chapter04; import java.util.*; public class Code_22 { public static void main(String[] args) { String string1,string2; System.out.print("Enter string s1: "); Scanner input = new Scanner(System.in); string1 = input.nextLine(); System.out.print("Enter string s2: "); string2 = input.nextLine(); System.out.println(string1.contains(string2) ?string2 + " is a substring of " + string1 :string2 + " is not a substring of " + string1); input.close(); } } -
9瓮床、在這里插入圖片描述
package chapter04; import java.util.*; public class Code_24 { public static void main(String[] args) { String city1,city2,city3; Scanner inputScanner = new Scanner(System.in); System.out.print("Enter the first city: "); city1 = inputScanner.nextLine(); System.out.print("Enter the second city: "); city2 = inputScanner.nextLine(); System.out.print("Enter the third city: "); city3 = inputScanner.nextLine(); if(city1.compareTo(city2) > 0) // city1 > city2 { if(city2.compareTo(city3) > 0) // city2 > city3 System.out.println("The three cities in alphabetical order are " + city1 + " " + city2 + " " + city3); else //city2 < city3 { if(city1.compareTo(city3) > 0) // city1 > city3 System.out.println("The three cities in alphabetical order are " + city2 + " " + city3 + " " + city1); else // city1 < city3 System.out.println("The three cities in alphabetical order are " + city2 + " " + city1 + " " + city3); } } else // city1 < city2 { if(city1.compareTo(city3) > 0) // city1 > city3 System.out.println("The three cities in alphabetical order are " + city3 + " " + city1 + " " + city2); else //city1 < city3 { if(city2.compareTo(city3) > 0) // city2 > city3 System.out.println("The three cities in alphabetical order are " + city1 + " " + city3 + " " + city2); else // city2 < city3 System.out.println("The three cities in alphabetical order are " + city1 + " " + city2 + " " + city3); } } inputScanner.close(); } } - 10盹舞、[圖片上傳失敗...(image-a71146-1601915130907)]
package chapter04; public class Code_25 { public static void main(String[] args) { char char1,char2,char3,char4,char5,char6,char7; char1 = (char)(65 + (int)(Math.random() * 26)); char2 = (char)(65 + (int)(Math.random() * 26)); char3 = (char)(65 + (int)(Math.random() * 26)); char4 = (char)(48 + (int)(Math.random() * 10)); char5 = (char)(48 + (int)(Math.random() * 10)); char6 = (char)(48 + (int)(Math.random() * 10)); char7 = (char)(48 + (int)(Math.random() * 10)); System.out.println("The vehicle plate numbers is " + char1+char2+char3+char4+char5+char6+char7); } }
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1渔期、
