Is the method read(byte b[], int off, int len) in InputStream same as the method read(byte b[], int off, int len) in FileInputStream?

Question

I am a new Java programmer. When I read source code of Java 17, I want to know how the method of read(byte b[], int off, int len) works in FileInputStream, FileInputStream's read method . I found it returns readBytes which is a native method, FileInputStream's native readBytes method . I didn't learn C code, so I can't read OpenJDK's source code. When I read Java official documen, I noticed that sentences in FileInputStream read(byte b[], int off, int len) 's description: "See Also:InputStream.read()" ( Java official documentation ). I really found a method in InputStream with the same name and parameters.

So, I want to ask, are these two read methods the same? InputStream's read method

Can I just read InputStream's read(byte b[], int off, int len) to replace the native read method in FileInputStream?

I didn't learn C code, so I can't read OpenJDK's source code. I try to resolve my question with Java official documentation.

Answer 1

FileInputStream extends InputStream and overrides read in InputStream . Its difference can be found in the documentation . They are not the same.

To be more specific, in FileInputStream , its readBytes calls IO_read (which finally calls read function in C) one time to read files.

nread = IO_Read(fd, buf, len);

While in InputStream , it calls read() byte by byte.

int c = read();
if (c == -1) {
    return -1;
}
b[off] = (byte)c;

int i = 1;
try {
    for (; i < len ; i++) {
        c = read();
        if (c == -1) {
            break;
        }
        b[off + i] = (byte)c;
    }
} catch (IOException ee) {
}

And because of its inheritance, you can call InputStream 's read using super keyword.