String案例之模拟用户3次登录：

 1  public static void main(String[] args) {
 2         //定义正确的登录名和密码
 3         String rightName = "admin";
 4         String rightPassword = "123456";
 5         //定义一个扫描器对象接收用户输入的数据
 6         Scanner sc = new Scanner(System.in);
 7 
 8         for (int i = 0; i < 3; i++) {
 9             System.out.println("输入登录名：");
10             String inputName = sc.next();
11             System.out.println("输入密码：");
12             String inputPassword = sc.next();
13             if (rightName.equals(inputName) && rightPassword.equals(inputPassword)){
14                 System.out.println("登录成功！");
15                 break;
16             }
17             else {
18                 System.out.println("登录失败~");
19                 System.out.println("你还有" + (2-i) + "次机会！");
20             }
21         }
22     }

String案例之随机生成5位数验证码：

 1     public static void main(String[] args){
 2         //1、定义可能出现的全部信息
 3         String allChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 4         //2、定义一个5次的循环，每循环一次取出一个字符
 5         String randCode = "";
 6         Random rand = new Random();
 7         for (int i = 0; i < 5; i++) {
 8             int randNumber = rand.nextInt(allChars.length()-1); //范围 [0 ~ x)
 9             randCode += allChars.charAt(randNumber);
10         }
11         System.out.println("你好，你的验证码为：" + randCode);
12     }

String案例之手机号码隐藏（以字符串的形式从键盘中接收一个手机号，将中间四位号码隐藏为*，最终效果为：155****5986）：

 1     public static void main(String[] args){
 2         //1、定义一个扫描器对象用于接收用户输入的号码
 3         Scanner sc = new Scanner(System.in);
 4         System.out.println("输入手机号：");
 5         String phoneNumber = sc.next();
 6         //2、截取字符串前三位、后四位、最后和****相加
 7         System.out.println(phoneNumber);
 8         String formerThree = phoneNumber.substring(0,3);
 9         String laterFour = phoneNumber.substring(7);
10         String shieldNumber = formerThree + "****" + laterFour;
11         System.out.println(shieldNumber);
12     }

ArrayList模拟电影院排片系统：

1、定义一个Movie类：

 1 public class Movie {
 2     private String filmTitle; //影片名
 3     private double grade; //评分
 4     private String actor; //主演
 5 
 6     public Movie() {
 7     }
 8 
 9     public Movie(String filmTitle, double grade, String actor) {
10         this.filmTitle = filmTitle;
11         this.grade = grade;
12         this.actor = actor;
13     }
14 
15     public String getFilmTitle() {
16         return filmTitle;
17     }
18 
19     public void setFilmTitle(String filmTitle) {
20         this.filmTitle = filmTitle;
21     }
22 
23     public double getGrade() {
24         return grade;
25     }
26 
27     public void setGrade(double grade) {
28         this.grade = grade;
29     }
30 
31     public String getActor() {
32         return actor;
33     }
34 
35     public void setActor(String actor) {
36         this.actor = actor;
37     }
38 }

2、定义一个ArrayList集合存放Movie类的实例对象：

 1     public static void main(String[] args) {
 2         ArrayList<Movie> movies = new ArrayList<>();
 3         movies.add(new Movie("肖申克的救赎",9.8,"安迪"));
 4         movies.add(new Movie("迪迦奥特曼",9.9,"大古"));
 5         movies.add(new Movie("熊出没之夺宝雄兵",9.5,"光头强、熊大、熊二"));
 6         for (int i = 0; i < movies.size(); i++) {
 7             System.out.println("影片名：" + movies.get(i).getFilmTitle() + " " +
 8                     "评分:" + movies.get(i).getGrade() + " " +
 9                     "主演:" + movies.get(i).getActor());
10         }
11     }

ArrayList集合模拟学生信息搜索（在集合中根据一个学生的学号搜索是否存在该学生，存在则输出该生具体信息，不存在则给出相应提示）：

1、定义一个学生类

 1 public class Student {
 2     private String id; //学号
 3     private String name; //学生姓名
 4     private int age; //年龄
 5     private String className; //班级
 6 
 7     public Student() {
 8     }
 9 
10     public Student(String id, String name, int age, String className) {
11         this.id = id;
12         this.name = name;
13         this.age = age;
14         this.className = className;
15     }
16 
17     public String getId() {
18         return id;
19     }
20 
21     public void setId(String id) {
22         this.id = id;
23     }
24 
25     public String getName() {
26         return name;
27     }
28 
29     public void setName(String name) {
30         this.name = name;
31     }
32 
33     public int getAge() {
34         return age;
35     }
36 
37     public void setAge(int age) {
38         this.age = age;
39     }
40 
41     public String getClassName() {
42         return className;
43     }
44 
45     public void setClassName(String className) {
46         this.className = className;
47     }
48 }

2、定义一个ArrayList集合存储学生信息

 1 public static void main(String[] args){
 2         ArrayList<Student> students = new ArrayList<>();
 3         students.add(new Student("20180302","叶孤城",23,"护理1班"));
 4         students.add(new Student("20180303","东方不败",23,"推拿2班"));
 5         students.add(new Student("20180304","西门吹雪",26,"中医药学4班"));
 6         students.add(new Student("20180305","梅超风",26,"神经科2班"));
 7 
 8         for (int i = 0; i < students.size(); i++) {
 9             System.out.println("学号     " + "\t\t\t" + "姓名" + "\t\t\t" + "    年龄" + "\t\t\t" + "  班级");
10             System.out.println(students.get(i).getId() + "\t\t\t" + students.get(i).getName() + "\t\t\t" +
11                     students.get(i).getAge() + "\t\t\t" + students.get(i).getClassName());
12         }
13 
14         //3、提供一个方法，传入ArrayList集合和学号可以得到学生对象
15         Scanner sc = new Scanner(System.in);
16         while (true) {
17             String inputId = sc.next();
18             Student ret = serachStuIofoById(students,inputId);
19             if(ret == null){
20                 System.out.println("不存在该学生");
21             }
22             else {
23                 System.out.println("找到了");
24                 System.out.println("学号：" + ret.getId() +
25                         "姓名：" + ret.getName() +
26                         "年龄：" + ret.getAge() +
27                         "班级：" + ret.getClassName());
28                 break;
29             }
30         }
31     }
32 
33     //根据学号在集合中查找学生
34     private static Student serachStuIofoById(ArrayList<Student> students, String id) {
35         for (int i = 0; i < students.size(); i++) {
36             if(id.equals(students.get(i).getId())){
37                 return students.get(i);
38             }
39         }
40         return null;
41     }