Java 从另一个类调用数组

Question

我正在尝试将对象的 arrayList 存储到从数组 ipvalue[] 创建的文本文件中，该数组在另一个类中实例化。我的问题是，每当我尝试将数组从 Mainframe 类加载到 Arraystorage 类时，它会将整个数组显示为空输出。我想问题是数组数据是在 Mainframe 方法中生成的，当我从另一个类调用数组时，它只是在初始化时获取数组。所以我的问题是如何在为数组赋值后而不是在初始化时访问数组。

new String[50] 
mainframe class:



public class Mainframe extends javax.swing.JFrame {
static int ipcounter = 0;
public static String[] ipvalue = new String [50];


/**
 * String a[]Creates new form Mainframe
 */
    public Mainframe() {
         try {
        initComponents();
        this.setLocation(500,250);
        Nettest.main(null);
        Display.setText(Nettest.indicator);
        Arraystorage.main(null);
        Path path = Paths.get("ipcounter.txt");

         File file = new File("ipcounter.txt");


         FileReader in = new FileReader("ipcounter.txt");
        BufferedReader br = new BufferedReader(in);

        readline = Integer.parseInt(br.readLine()); 
        in.close();
        ipcounter = readline;

         if(ip.tracker.Nettest.status == true){
         ipvalue[ipcounter] = Readipfromurl.inputLine;
       //  crosscheck();

        Writer writer = null;
         writer = new BufferedWriter(new OutputStreamWriter(
         new FileOutputStream("ipcounter.txt"), "utf-8"));
          writer.write(String.valueOf(ipcounter+1));

          writer.close();
         System.out.println(ipvalue[ipcounter]);
          ipcounter++;


arraystorage class:


public class Arraystorage implements Serializable{
   public static void main(String[] args) throws 
 ClassNotFoundException { 

   ArrayList<String> list = new ArrayList<String>();
  for (int i=0; i<50;i++){
  list.add(Mainframe.ipvalue[i]);}
   try {
       PrintWriter out = new PrintWriter(new BufferedWriter(new 
  FileWriter("data.txt")));
   for( int x = 0; x < list.size(); x++)
 {
 out.println(list.get(x));
 }

   out.close();


   } catch (IOException ex) {

 Logger.getLogger(Arraystorage.class.getName()).log(Level.SEVERE, 
null, ex);
   }

Answer 1

简而言之，您没有调用用数据填充数组的 Mainframe()。在需要使用 ipvalue 数组之前，您应该在 main 方法中执行此操作。因此，只需在 Mainframe 实例上调用此方法即可:

public static void main(String[] args) throws  ClassNotFoundException { 

  ArrayList<String> list = new ArrayList<String>();
  Mainframe frame = new Mainframe();
  frame.Mainframe();
  for (int i=0; i<50;i++){
  list.add(Mainframe.ipvalue[i]);
  }
  ... // do the rest

长话短说，请至少阅读Oracle Java tutorial用于命名约定、代码结构等的 Java 基础知识