Java SE入门（十一）——IO与集合练习

Java SE入门（十一）——IO与集合练习
　　iwehdio的博客园：https://www.cnblogs.com/iwehdio/

1、IO练习

• 键盘录入学生信息存入集合，然后存入文件的步骤：
  1. 定义学生类。
  2. 创建集合对象。
  3. 写方法实现键盘录入学生信息，并把学生对象作为元素添加到集合。
  4. 创建输出缓冲流对象。
  5. 遍历集合，得到每一个学生信息，并将其按一定格式写入文件。

public static void main(String[] args) throws IOException {
    
    ArrayList<Student> array = new ArrayList<Student>();
    
    addStudent(array);
    addStudent(array);
    addStudent(array);
    
    BufferedWriter bw = new BufferedWriter(new FileWriter("d.txt"));
    
    for(int x=0;x<array.size();x++){
        Student s = array.get(x);
        StringBuilder sb = new StringBuilder();
        sb.append(s.getId()).append(", ").append(s.getName()).append(", ").append(s.getAge()).append(", ").append(s.getAddress());
        
        bw.write(sb.toString());
        bw.newLine();
        bw.flush();
        
    }
    
    bw.close();
}

public static void addStudent(ArrayList<Student> arr){
    Scanner sc = new Scanner(System.in);
    String id;
    while(true){
        System.out.println("学号");
        id = sc.nextLine();
        boolean flag = false;
        for(int x=0;x<arr.size();x++){
            Student s = arr.get(x);
            if(s.getId().equals(id)){
                System.out.println("学号重复");
                flag = true;
                break;
            }
        }
        if(flag){
            System.out.println("重新输入");
        }else{
            break;
        }
    }
    
    System.out.println("姓名");
    String name = sc.nextLine();
    System.out.println("年龄");
    String age = sc.nextLine();
    System.out.println("地址");
    String address = sc.nextLine();
    
    Student s = new Student();
    s.setId(id);
    s.setName(name);
    s.setAge(age);
    s.setAddress(address);
    
    arr.add(s);
    System.out.println("添加成功");
    
}

• 将文本数据中的数据读到集合中并遍历集合：
  1. 定义学生类。
  2. 创建输入缓冲流对象。
  3. 创建集合对象。
  4. 读取文件数据，并把数据按照一定格式进行分割，赋值到学生对象，并把学生对象作为元素存储到集合。
  5. 遍历集合。

public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new FileReader("d.txt"));
    ArrayList<Student> array = new ArrayList<Student>();
    
    String line;
    while((line=br.readLine())!=null){
        Student s = new Student();
        String[] strArr = line.split(", ");
        s.setId(strArr[0]);
        s.setName(strArr[1]);
        s.setAge(strArr[2]);
        s.setAddress(strArr[3]);
        array.add(s);
    }
    br.close();
    
    for(int x=0;x<array.size();x++){
        Student s = array.get(x);
        System.out.println(s.getId()+"\t"+s.getName()+"\t"+s.getAge()+"\t"+s.getAddress());
        
    }
}

2、IO版学生管理系统

• 把学生对象作为元素与集合联系起来。
• 把文件用读写与集合联系起来。
• 用集合做中介将学生对象和文件联系起来。
• 传入方法的是文件路径，然后在方法中在读写文件。

public static void main(String[] args) throws IOException {
    System.out.println("----进入系统-----");
    String filename = "Student.txt";
    
    while(true){

        System.out.println("1.查看");
        System.out.println("2.添加");
        System.out.println("3.删除");
        System.out.println("4.修改");
        System.out.println("5.退出");
        System.out.println("请输入");
        Scanner sc = new Scanner(System.in);
        String choice = sc.nextLine();
        
        switch(choice){
        case "1":
            findStudent(filename);
            break;
        case "2":
            addStudent(filename);
            break;
            
        case "3":
            deletStudent(filename);
            break;
            
        case "4":
            updateStudent(filename);
            break;
        case "5":
        default:
            System.out.println("退出成功");
            System.exit(0);  //JVM退出
            break;
        }

    }
}
public static void findStudent(String filename) throws IOException{
    ArrayList<Student> arr = new ArrayList<Student>();
    readData(filename, arr);
    if(arr.size() ==0 ){
        System.out.println("无数据信息");
    }else{
        System.out.println("学号\t姓名\t年龄\t居住地");
        for(int x=0;x<arr.size();x++){
            Student s = arr.get(x);
            System.out.println(s.getId()+"\t"+s.getName()+"\t"+s.getAge()+"\t"+s.getAddress());
        }
    }
    writeData(filename, arr);
}

public static void addStudent(String filename) throws IOException{
    ArrayList<Student> arr = new ArrayList<Student>();
    readData(filename, arr);
    Scanner sc = new Scanner(System.in);
    String id;
    while(true){
        System.out.println("学号");
        id = sc.nextLine();
        boolean flag = false;
        for(int x=0;x<arr.size();x++){
            Student s = arr.get(x);
            if(s.getId().equals(id)){
                System.out.println("学号重复");
                flag = true;
                break;
            }
        }
        if(flag){
            System.out.println("重新输入");
        }else{
            break;
        }
    }
    
    System.out.println("姓名");
    String name = sc.nextLine();
    System.out.println("年龄");
    String age = sc.nextLine();
    System.out.println("地址");
    String address = sc.nextLine();
    
    Student s = new Student();
    s.setId(id);
    s.setName(name);
    s.setAge(age);
    s.setAddress(address);
    
    arr.add(s);
    System.out.println("添加成功");
    writeData(filename, arr);
}

public static void deletStudent(String filename) throws IOException{
    ArrayList<Student> arr = new ArrayList<Student>();
    readData(filename, arr);
    Scanner sc = new Scanner(System.in);
    System.out.println("删除学生学号");
    String id = sc.nextLine();
    int index = -1;
    
    for(int x=0;x<arr.size();x++){
        Student s = arr.get(x);
        if(s.getId().equals(id)){
            index = x;
            break;
        }
    }
    
    if(index == -1){
        System.out.println("不存在此学号");
    }else{
        arr.remove(index);
        System.out.println("删除成功");
    }
    writeData(filename, arr);
}

public static void updateStudent(String filename) throws IOException{
    ArrayList<Student> arr = new ArrayList<Student>();
    readData(filename, arr);
    Scanner sc = new Scanner(System.in);
    System.out.println("修改学生学号");
    String id = sc.nextLine();
    int index = -1;
    
    for(int x=0;x<arr.size();x++){
        Student s = arr.get(x);
        if(s.getId().equals(id)){
            index = x;
            break;
        }
    }
    
    if(index == -1){
        System.out.println("不存在此学号");
    }else{
        System.out.println("新姓名");
        String name = sc.nextLine();
        System.out.println("新年龄");
        String age = sc.nextLine();
        System.out.println("新地址");
        String address = sc.nextLine();
        Student s = new Student();
        s.setId(id);
        s.setName(name);
        s.setAge(age);
        s.setAddress(address);
        arr.set(index, s);
        System.out.println("修改成功");
    }
    writeData(filename, arr);
}

public static void readData(String filename,ArrayList<Student> arr) throws IOException{
    BufferedReader br = new BufferedReader(new FileReader(filename));
    
    String line;
    while((line=br.readLine())!=null){
        String[] data = line.split(", ");
        Student s = new Student();
        s.setId(data[0]);
        s.setName(data[1]);
        s.setAge(data[2]);
        s.setAddress(data[3]);
        arr.add(s);
    }
    br.close();
}

public static void writeData(String filename,ArrayList<Student> arr) throws IOException{
    BufferedWriter bw = new BufferedWriter(new FileWriter(filename));
    
    for(int x=0;x<arr.size();x++){
        Student s = arr.get(x);
        StringBuilder sb = new StringBuilder();
        sb.append(s.getId()).append(", ").append(s.getName()).append(", ").append(s.getAge()).append(", ").append(s.getAddress());
        bw.write(sb.toString());
        bw.newLine();
        bw.flush();
    }
    bw.close();
}

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