import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class D316 {// 有问题
    public static void main(String[] args) {
        try {
            FileInputStream fileinputstream = new FileInputStream(new File("C:"+File.separator+"a.txt"));//这里有问题
            InputStreamReader inputstreamreader = new InputStreamReader(
                    fileinputstream);
            FileOutputStream fileoutputstream = new FileOutputStream(new File(
                    "C:"+File.separator+"b.txt"));//还有这里
            OutputStreamWriter outputstreamwriter = new OutputStreamWriter(
                    fileoutputstream);
            int ch;
            while ((ch = inputstreamreader.read()) != -1) {
                System.out.print((char)ch + " ");
                outputstreamwriter.write(ch);
            }
            inputstreamreader.close();
            outputstreamwriter.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

------解决方案--------------------
ava.io.FileNotFoundException: C:\a.txt (系统找不到指定的文件。)

这个是个文件Copy程序,你的源文件c:\a.txt必须存在,先用编辑器(如记事本)在C:\建一个a.txt程序就可以了