Maximum tcp port number constant in java

Question

Is there a public constant for the maximum TCP port number (65535) defined in java or a common library such as Apache Commons, that I could refer to from my code (instead of using the integer hardcoded)?

it's not going to change (ever) unless they redesign TCP to allow a higher port number (which isn't needed); 0xffff is a quick way to place it down — ratchet freak
– ratchet freak, Commented Aug 22, 2014 at 7:46
I would create a local constant in the class where you need it. — Florian F
– Florian F, Commented Aug 22, 2014 at 7:51
I think the question is relevant. Why would we have to define a well-known constant? — Morgan Courbet
– Morgan Courbet, Commented Aug 24, 2014 at 21:29
I just don't see why I have to define it myself as it is defined by an RFC (ietf.org/rfc/rfc793.txt), and it's regarding something as broadly used as TCP, so you'd expect it to be defined somewhere common and logical. I personally expected it in java's java.net.Socket, because that one uses ports of course and out of java's own classes, it's the class that's based on TCP the most. — dammkewl
– dammkewl, Commented Aug 25, 2014 at 5:47

Thirler · Accepted Answer · 2015-03-03 13:28:14Z

17

I'm afraid there is none you can use.

Looking at the source code of Java 8 I see the following code used by the Socket class to verify a valid port in several functions:

private static int checkPort(int port) {
    if (port < 0 || port > 0xFFFF)
        throw new IllegalArgumentException("port out of range:" + port);
    return port;
}

This can be found in java.net.InetSocketAddress.checkPort(int)

As you can see Java itself doesn't use a named constant either.

A search of the code turns up the following hit in java.net.HostPortrange:

static final int PORT_MIN = 0;
static final int PORT_MAX = (1 << 16) -1;

But as you can see this isn't a public reference. Another private reference turns up in java.net.SocketPermission.

So after the inspection above, I conclude there is none available in the Java API.

edited Mar 3, 2015 at 13:28

answered Mar 3, 2015 at 12:46

Thirler

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