FileInputStream的int read()、int read(byte[] b)、int read(byte[] b, int off, int len)

explain:

int read() ：

(1) Read a byte of data and return (return in int type)
(2) Call again to read the next unread byte
(3) Return -1 at the end of the file (no real data has been read)
Demo file

code

FileInputStream fileInputStream = new FileInputStream(new File("E:\\aa.txt"));
        int read1 = fileInputStream.read();
        int read2 = fileInputStream.read();
        int read3 = fileInputStream.read();
        System.out.println(read1);
        System.out.println(read2);
        System.out.println(read3);

output

int read(byte[] b) ：

(1) The read data is stored in the b array, and b.length bytes are read at a time
(2) The actual length of the read data is returned (it is possible that the length of the b array is 100, but the actual data is only 5, then return 5 )
(3) Call again to read from the next unread byte
(4) Return -1 at the end of the file (no real data has been read)
demo file

code

FileInputStream fileInputStream = new FileInputStream(new File("E:\\aa.txt"));

        byte[] bytes1=new byte[5];
        int read1 = fileInputStream.read(bytes1);
        System.out.println(read1);
        System.out.println(Arrays.toString(bytes1));

        byte[] bytes2=new byte[5];
        int read2 = fileInputStream.read(bytes2);
        System.out.println(read2);
        System.out.println(Arrays.toString(bytes2));

        byte[] bytes3=new byte[5];
        int read3 = fileInputStream.read(bytes3);
        System.out.println(read3);
        System.out.println(Arrays.toString(bytes3));

output

int read(byte[] b, int off, int len) ：

(1) Store the read data into b
(2) Start storing from the array subscript off (including), read len bytes (len<=b.length-off)
(3) Return the read data Real length
(4) call again to read from the next unread byte
(5) return -1 at the end of the file (no real data is read)
demo file

the code

FileInputStream fileInputStream = new FileInputStream(new File("E:\\aa.txt"));
        
        byte[] bytes1=new byte[5];
        int read1 = fileInputStream.read(bytes1, 2, 3);
        System.out.println(read1);
        System.out.println(Arrays.toString(bytes1));

        byte[] bytes2=new byte[5];
        int read2 = fileInputStream.read(bytes2, 2, 3);
        System.out.println(read2);
        System.out.println(Arrays.toString(bytes2));

        byte[] bytes3=new byte[5];
        int read3 = fileInputStream.read(bytes2, 2, 3);
        System.out.println(read3);
        System.out.println(Arrays.toString(bytes3));

output