从集合到文件 和从文件到集合

集合到文件

需求和思路

代码演示

package Demo1;

import java.sql.PreparedStatement;

/**
 * @auther 黄磊
 * @2021/8/20 17:00
 **/
public class Student {
    private String ID;
    private String name;
    private int age;
    private String adress;

    public Student() {
    }

    public Student(String ID, String name, int age, String adress) {
        this.ID = ID;
        this.name = name;
        this.age = age;
        this.adress = adress;
    }

    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 getAdress() {
        return adress;
    }

    public void setAdress(String adress) {
        this.adress = adress;
    }
    
    //这个可以写 也可以不写 我是方便测试才写的 
    @Override
    public String toString() {
        return "Student{" +
                "ID='" + ID + '\'' +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", adress='" + adress + '\'' +
                '}';
    }
}


package Demo1;
import java.io.*;
import java.util.ArrayList;

/**
 * @auther 黄磊
 * @2021/8/20 17:03
 **/
public class ArrayListToFileDemo {
    public static void main(String[] args) throws IOException {
        ArrayList<Student> array = new ArrayList<>();
        BufferedWriter fw = new BufferedWriter(new FileWriter("Previous\\123.java"));

        Student s1 = new Student("itheima001", "林青霞", 30, "西安");
        Student s2 = new Student("itheima002", "张曼玉", 35, "武汉");
        Student s3 = new Student("itheima003", "王祖贤", 33, "郑州");

        array.add(s1);
        array.add(s2);
        array.add(s3);

        for (Student s : array) {
//            String info = s.getID() + "," + s.getName() + "," + s.getAge() + "," + s.getAdress();
            //此处也可以用StringBuilder方法
            StringBuilder sb = new StringBuilder();
            String info = sb.append(s.getID()).append(",").append(s.getName()).append(",").
                    append(s.getAge()).append(",").append(s.getAdress()).toString();
            fw.write(info);
            fw.newLine();//重要
            fw.flush();
        }
        fw.close();

    }
}

效果

会在Previous（相对路径）下创建一个123.java的文件,内容如下

从文件到集合

需求和思路

代码演示

//共用一个Student类
package Demo1;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
/**
 * @auther 黄磊
 * @2021/8/20 17:20
 **/
public class FileToArrayListDemo {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("Previous\\123.java"));
        ArrayList<Student> array = new ArrayList<>();
        String Line;
        while ((Line = br.readLine()) != null) {
            Student s = new Student();
//            ss.setID(Line.split(",")[0]);
//            ss.setName(Line.split(",")[1]);
//            ss.setAge(Integer.parseInt(Line.split(",")[2]));
//            ss.setAdress(Line.split(",")[3]);
//            array.add(ss);
            //代码缺点：4行代码都用split()方法 可以简化代码
            String[] split = Line.split(",");
            s.setID(split[0]);
            s.setName(split[1]);
            s.setAge(Integer.parseInt(split[2]));
            s.setAdress(split[3]);
            array.add(s);
        }
        for (Student ss : array) {
            System.out.println(ss.getID() + "," + ss.getName() + "," + ss.getAge() + "," + ss.getAdress());
        }
    }
}

 结果

在控制台打印集合里面的内容