Hardcoding an IP address into source code is a bad idea for several reasons:

a recompile is required if the address changes
it forces the same address to be used in every environment (dev, sys, qa, prod)
it places the responsibility of setting the value to use in production on the shoulders of the developer
it allows attackers to decompile the code and thereby discover a potentially sensitive address

Recommended Secure Coding Practices

Noncompliant Code Example

String ip = "192.168.12.42"; // Noncompliant
Socket socket = new Socket(ip, 6667);

No issue is reported for the following cases because they are not considered as sensitive:

Loopback addresses 127.0.0.0/8 in CIDR notation (from 127.0.0.0 to 127.255.255.255)
Broadcast address 255.255.255.255
Non routable address 0.0.0.0