java - 为什么它不读取？

Question

我想问一下我的程序有什么问题..我的程序是关于堆栈的，没有错误，但我的问题是，我们的要求是在堆栈中进行所有操作，然后，即使您关闭程序，下次打开它时，仍应显示以前的数据..我使用了文件写入器和文件读取器，但是每次我关闭它，然后再次打开它，以前的数据都不会出现。有什么建议吗？谢谢..这是我的程序..

import java.util.*;
import java.awt.*;
import java.io.*;
import javax.swing.*;
import java.awt.event.*;
public class STACKS extends JFrame implements ActionListener
{
    private JButton push,pop,peek,display,exit;
    private JLabel Stack;
    static int arr[],x=0,b=0,xy=0,c=0;
    static String in="",INDEX="",d="",s="";
    static String id[]={};

    public STACKS()
    {
        super("STACKS MENU!^_^");
        Container c=getContentPane();
        c.setLayout(new FlowLayout());
        Stack=new JLabel("STACKS MENU!^_^");    c.add(Stack);
        push=new JButton("Push!^-^");
        pop=new JButton("Pop!^-^");
        peek=new JButton("Peek!^-^");
        display=new JButton("Display!^-^");
        exit=new JButton("Exit!^-^");
        push.addActionListener(this);           c.add(push);
        pop.addActionListener(this);            c.add(pop);
        peek.addActionListener(this);           c.add(peek);
        display.addActionListener(this);        c.add(display);
        exit.addActionListener(this);           c.add(exit);
        setVisible(true);
        setSize(150,250);
    }
    public static void saveMe() throws IOException
    {
        File data1=new File("Sample.txt");      //a file was created...
        PrintWriter out=new PrintWriter(new BufferedWriter(new FileWriter(data1,true)));
        for(int x=0;x<4;x++)
        {
            out.write(":"+arr[x]);  xy=1;           //here in this section, I put : in every elements inside the array..
        }
        out.close();

    }
    public static void readMe() throws IOException
    {
        Scanner txtFile=(new Scanner("Sample.txt"));

        for(int y=0;x<id.length;y++)
        {
            s=txtFile.nextLine();
            id=s.split(":");
            arr[y]=Integer.parseInt(id[y]);
        }

    }
    public  void actionPerformed(ActionEvent a)
    {
        try
        {
            readMe();                               //here is where the previous data will be read..
        }
        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null,"File not found! readme !^,^");
        }
        if (xy==0)
        {
            INDEX=JOptionPane.showInputDialog(null,"Enter LENGTH of the array!");
            c=Integer.parseInt(INDEX); xy=1;
            arr=new int[c];
        }
        if(a.getSource()==push)
        {
            in=JOptionPane.showInputDialog(null,"Enter integer to be pushed!");
            b=Integer.parseInt(in);
            arr[x]=b;   x+=1;
            if(x==c)
            {
                JOptionPane.showMessageDialog(null,"WARNING! The stacks are full, please pop something!^-^");
            }
            if(x>c)
            {
                JOptionPane.showMessageDialog(null,"Sorry, the stacks are full,please pop something first!^-^");
                x-=1;
            }
        }
        else if(a.getSource()==pop)
        {

            arr[x-1]=0;x-=1;
            JOptionPane.showMessageDialog(null,"The value has been popped!^-^");
            if(x==0)
            {
                JOptionPane.showMessageDialog(null,"The stacks are empty, push something!^-^");
            }

        }
        else if(a.getSource()==peek)
        {
            JOptionPane.showMessageDialog(null,"The value is "+arr[x-1]+"! ^-^");
        }
        else if(a.getSource()==display)
        {
            for(int y=c-1;y>-1;y--)
            {
                d+="*** "+arr[y]+" ***\n";
            }
            JOptionPane.showMessageDialog(null,"The value inside the stacks are:\n"+d);
            d="";
        }
        else if(a.getSource()==exit)
        {
            System.exit(0);
        }
            try
        {
            saveMe();                   //here is where the file will be saved..
        }
        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null,"File not found!^,^");
        }
    }
    public static void main(String args[])
    {
        STACKS pot=new STACKS();
        pot.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }
}

Answer 1

实际上这里存在很多问题。

就亚历山大的回答而言，您在每次推送/弹出调用后都会保存，所以 saveMe()正在被调用。

在 saveMe()不过，你写 :在堆栈的第一个元素之前，因此读回它总是会给出一个额外的空白元素。在写入 : 之前检查 x != 0 是否.

在 readMe() ，您正在调用nextLine()对于 id.length，它在两个方面是不正确的:

1. 当您启动程序时，id 的长度将为零。您不应该使用x<id.length作为 for 的结束条件循环(x 无论如何都是错误的，在你的上下文中它应该是 y)。使用txtFile.hasNext()检查是否还有更多堆栈元素需要读取。
2. 您的文件完全在一行上包含堆栈，而不是多行。您应该做的是将扫描仪的分隔符设置为 :与 textFile.useDelimiter(":") ，然后调用next() 。另请记住，除非您更正 saveMe()开头会有一个额外的空白元素。

也在 readMe() ，根据 Nicklamort 的回答，您需要调用 new Scanner(new File("Sample.txt"))打开实际文件。

新的 readMe() 示例

public static void readMe() throws IOException
{
    Scanner txtFile=(new Scanner(new File("Sample.txt")));
    int y = 0;
    txtFile.useDelimiter(":");
    while(txtFile.hasNext())
    {
        arr[y]=txtFile.nextInt();
        y++;
    }

}

新的 saveMe() 示例

public static void saveMe() throws IOException
{
    File data1=new File("Sample.txt");      //a file was created...
    PrintWriter out=new PrintWriter(new BufferedWriter(new FileWriter(data1,false))); // don't append, overwrite existing data since we are saving the entire stack each time
    for(int x=0;x<arr.length;x++)
    {
        if(x != 0) { out.write(":"); }           //here in this section, I put : in every elements inside the array..
        out.write(arr[x]);  xy=1;
    }
    out.flush(); // force writing to disk
    out.close();
}