RandomAccessFile

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;

public class RafDemo {

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub

        File demo = new File("demo");
        
        if(!demo.exists())
            demo.mkdir();
        
        File file = new File(demo,"raf.dat");
        if(!file.exists())
            file.createNewFile();
        
        RandomAccessFile raf = new RandomAccessFile(file,"rw");
        
        raf.write('A');
        System.out.println(raf.getFilePointer());
        raf.write('B');
        System.out.println(raf.getFilePointer());
        
        int i = 0x7fffffff;
        
//        int j = i >>> 24;
//        System.out.println( Integer.toHexString(j));
        
        raf.write(i >>> 24);
        raf.write(i >>> 16);
        raf.write(i >>> 8);
        raf.write(i);
        System.out.println(raf.getFilePointer());
        
        raf.writeInt(i);
        
        String s = "中";
        byte[] gbk = s.getBytes("gbk");
        raf.write(gbk);
        
        System.out.println(raf.length());
        
        
        raf.seek(0);
        
        byte[] buf = new byte[(int)raf.length()];
        
        raf.read(buf);
        System.out.println(Arrays.toString(buf));
        
        String s1 = new String(buf,"gbk");
        System.out.println(s1);
        
        raf.close();
    }

}

Console:

1
2
6
12
[65, 66, 127, -1, -1, -1, 127, -1, -1, -1, -42, -48]
AB??????中