java - 将 ArrayList 保存到文本文件

Question

我一直在尝试获取一个 ArrayList 以保存到一个文件中。我可以看到它正在创建文本文件，但文本文件中没有任何内容，只是空白。

这是ArrayList的主要代码，带有保存选项的开关。

static int input, selection, i = 1;
static ArrayList<Animals> a;

// Main Method
public static void main(String[] args){

    // Create an ArrayList that holds different animals
    a = new ArrayList<>();
    a.add(new Animals(i++, "Bear", "Vertebrate", "Mammal"));
    a.add(new Animals(i++, "Snake", "Invertebrate", "Reptile"));
    a.add(new Animals(i++, "Dog", "Vertebrate", "Mammal"));
    a.add(new Animals(i++, "Starfish", "Invertebrates", "Fish"));

    while (true) {
        try {
            System.out.println("\nWhat would you like to do?");
            System.out.println("1: View List\n2: Delete Item\n3: Add Item\n4: Edit Item\n5: Save File\n0: Exit");
            selection = scanner.nextInt();
            if(selection != 0){
                switch (selection) {
                    case 1:
                        ViewList.view();
                        Thread.sleep(4000);
                        break;
                    case 2:
                        Delete.deleteItem();
                        Thread.sleep(4000);
                        break;
                    case 3:
                        Add.addItem();
                        Thread.sleep(4000);
                        break;
                    case 4:
                        Edit.editItem();
                        Thread.sleep(4000);
                        break;
                    case 5:
                        Save.saveToFile("animals.txt", a);
                        Thread.sleep(4000);
                        break;

这是我写的处理文件。

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;

public class Save extends ALProgram{
     public static void saveToFile(String fileName, ArrayList list){
            Path filePath = Paths.get(fileName);
            try{
                System.out.println("File Saved");
                Files.write(filePath, list, Charset.defaultCharset());
            }catch(IOException e){
                e.printStackTrace();
            }

     }
}

这是动物类

class Animals {

public int id;
public String type, vertebrate, aclass;

public Animals(int id, String type, String vertebrate, String aclass) {
    this.id = id;
    this.type = type;
    this.vertebrate = vertebrate;
    this.aclass = aclass;

}

public int getID() {
    return id;
}

public String getType() {
    return type;
}

public String getVert() {
    return vertebrate;
}

public String getaclass() {
    return aclass;
}

}

Answer 1

有两个变化:

1. 您的类需要实现 CharSequence 才有资格传递给 Files.write。

2. 您需要覆盖 toString 方法以指定您的内容在保存时的外观。经过以上两个更改后，我可以看到输出。

       class Animals implements CharSequence {
   
           public int id;
           public String type, vertebrate, aclass;
   
   public Animals(int id,String type,String vertebrate,String aclass) {
   this.id = id;
   this.type = type;
   this.vertebrate = vertebrate;
               this.aclass = aclass;
           }
   
           public int getID() {
               return id;
           }
   
           public String getType() {
               return type;
           }
   
           public String getVert() {
               return vertebrate;
           }
   
           public String getaclass() {
               return aclass;
           }
   
           @Override
           public int length() {
               return toString().length();
           }
   
           @Override
           public char charAt(int index) {
               return toString().charAt(index);
           }
   
           @Override
           public CharSequence subSequence(int start, int end) {
               return toString().subSequence(start, end);
           }
   
           /* (non-Javadoc)
            * @see java.lang.Object#toString()
            */
           @Override
           public String toString() {
               return "Animals [id=" + id + ", type=" + type + ", vertebrate=" + vertebrate + ", aclass=" + aclass + "]";
           }
   
   
           }