java 求帮助 我这个怎么改变一下？

public class Demo4 {
    public static void main(String[] args) {
        //创建输入流对象
        FileInputStream inputStream=new FileInputStream(new File("a.txt"));
        FileInputStream in=new FileInputStream("a.txt");
        // read
        // read单个字节
        //readSinngle(in);
        // read字节数组
        //创建一个容器杯子
        byte[] bytes = new byte[1024];
        // readMulti(in , bytes);
        // read字节数组 的部分
        int readCount =0;
        try {
            readCount=in.read(bytes,0,bytes.length);
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println(new String(bytes,0,readCount));
        // close
        try {
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void readMUlti(FileInputStream in, byte[] bytes) throws IOException{
        int readCount =in.read();
        System.out.println(readCount);
        // 把字节数据转化为字符串利用String的构造方法
        String s = new String(bytes , 0 , readCount);
        System.out.println(s);
    }

    private static void readSingle(FileInputStream in) throws IOException{
        int readData =in.read();
        System.out.println(readData);
        int readData2 = in.read();
        System.out.println(readData2);
        int readData3 = in.read();
        System.out.println(readData3);
        int readData4 =in.read();
        System.out.println(readData4);
    }
}

        FileInputStream inputStream = null;
        FileInputStream in = null;
        //创建输入流对象
        try {
            inputStream = new FileInputStream(new File("a.txt"));
            in = new FileInputStream("a.txt");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }