运行程序一次后保留一个值？

Question

我正在制作一个程序，将歌曲的标题、艺术家和流派存储到数据文件中。像这样：

    public void writeSong(Song t) throws IOException {
    File myFile = new File(Song.getFileInput());
    RandomAccessFile write = new RandomAccessFile(myFile,"rw");
    write.writeChars(title);
    write.writeChars(artist);
    write.writeChars(genre);
    write.close();
}

在我这样做之后，我应该读取数据文件并像这样显示它的内容：

    public Song readSong() throws FileNotFoundException, IOException {

    File myFile = new File(Song.getFileInput());
    RandomAccessFile read = new RandomAccessFile(myFile, "rw");
    String readTitle = null, readArtist = null, readGenre = null;
    Song so = null;

    read.seek(0);
    for(int i = 0; i < title.length(); i++){
        readTitle += read.readChar();
    }

    read.seek(50);
    for(int i = 0; i < artist.length(); i++){
        readArtist += read.readChar();
    }

    read.seek(100);
    for(int i = 0; i < genre.length(); i++){
        readGenre += read.readChar();
    }

    so = new Song(readTitle, readArtist, readGenre);
    read.close();
    return so;
}

如果我将它分配给一个名为“songs.dat”的文件，它应该会从该文件中写入和读取歌曲。退出程序并再次运行后，我再次创建名为“songs.dat”的文件。但是当我想阅读和显示歌曲时，什么也没有发生。有没有人怎么解决这个问题？

Answer 1

RandomAccessFile.seek(long position) 设置要读取或写入的文件位置。

当您开始读取文件时，您使用read.seek(0) 将位置设置为0。但是从那里你不需要重置它：

public Song readSong() throws FileNotFoundException, IOException {

    File myFile = new File(Song.getFileInput());
    RandomAccessFile read = new RandomAccessFile(myFile, "rw");
    String readTitle = "", readArtist = "", readGenre = "";
    Song so = null;

    read.seek(0);
    for(int i = 0; i < title.length(); i++){
        readTitle += read.readChar();
    }

    for(int i = 0; i < artist.length(); i++){
        readArtist += read.readChar();
    }

    for(int i = 0; i < genre.length(); i++){
        readGenre += read.readChar();
    }

    so = new Song(readTitle, readArtist, readGenre);
    read.close();
    return so;
}

我还将您的字符串初始化为空字符串，因此您首先没有“空”字符串