常用API-->String、ArrayList

字符串存储的内存原理：

字符串常量池中的相同内容只会存储一份用来共享，每添加一个字符串对象就会产生新的字符串对象，并将其存放在堆内存中。

 

接下来看使用 new构造器 & 双引号 创建字符串对象的不同之处：

 

String案例之模拟用户3次登录：

 public static void main(String[] args) {
        //定义正确的登录名和密码
        String rightName = "admin";
        String rightPassword = "123456";
        //定义一个扫描器对象接收用户输入的数据
        Scanner sc = new Scanner(System.in);

        for (int i = 0; i < 3; i++) {
            System.out.println("输入登录名：");
            String inputName = sc.next();
            System.out.println("输入密码：");
            String inputPassword = sc.next();
            if (rightName.equals(inputName) && rightPassword.equals(inputPassword)){
                System.out.println("登录成功！");
                break;
            }
            else {
                System.out.println("登录失败~");
                System.out.println("你还有" + (2-i) + "次机会！");
            }
        }
    }

String案例之随机生成5位数验证码：

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

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）：

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

 

 

 

ArrayList模拟电影院排片系统：

1、定义一个Movie类：

public class Movie {
    private String filmTitle; //影片名
    private double grade; //评分
    private String actor; //主演

    public Movie() {
    }

    public Movie(String filmTitle, double grade, String actor) {
        this.filmTitle = filmTitle;
        this.grade = grade;
        this.actor = actor;
    }

    public String getFilmTitle() {
        return filmTitle;
    }

    public void setFilmTitle(String filmTitle) {
        this.filmTitle = filmTitle;
    }

    public double getGrade() {
        return grade;
    }

    public void setGrade(double grade) {
        this.grade = grade;
    }

    public String getActor() {
        return actor;
    }

    public void setActor(String actor) {
        this.actor = actor;
    }
}

2、定义一个ArrayList集合存放Movie类的实例对象：

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

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

public class Student {
    private String id; //学号
    private String name; //学生姓名
    private int age; //年龄
    private String className; //班级

    public Student() {
    }

    public Student(String id, String name, int age, String className) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.className = className;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className = className;
    }
}

2、定义一个ArrayList集合存储学生信息

public static void main(String[] args){
        ArrayList<Student> students = new ArrayList<>();
        students.add(new Student("20180302","叶孤城",23,"护理1班"));
        students.add(new Student("20180303","东方不败",23,"推拿2班"));
        students.add(new Student("20180304","西门吹雪",26,"中医药学4班"));
        students.add(new Student("20180305","梅超风",26,"神经科2班"));

        for (int i = 0; i < students.size(); i++) {
            System.out.println("学号     " + "\t\t\t" + "姓名" + "\t\t\t" + "    年龄" + "\t\t\t" + "  班级");
            System.out.println(students.get(i).getId() + "\t\t\t" + students.get(i).getName() + "\t\t\t" +
                    students.get(i).getAge() + "\t\t\t" + students.get(i).getClassName());
        }

        //3、提供一个方法，传入ArrayList集合和学号可以得到学生对象
        Scanner sc = new Scanner(System.in);
        while (true) {
            String inputId = sc.next();
            Student ret = serachStuIofoById(students,inputId);
            if(ret == null){
                System.out.println("不存在该学生");
            }
            else {
                System.out.println("找到了");
                System.out.println("学号：" + ret.getId() +
                        "姓名：" + ret.getName() +
                        "年龄：" + ret.getAge() +
                        "班级：" + ret.getClassName());
                break;
            }
        }
    }

    //根据学号在集合中查找学生
    private static Student serachStuIofoById(ArrayList<Student> students, String id) {
        for (int i = 0; i < students.size(); i++) {
            if(id.equals(students.get(i).getId())){
                return students.get(i);
            }
        }
        return null;
    }