Is it enough to encrypt then sign when using symmetric-key encryption? I'm doing some tests in Java, encrypting messages exchanged between two entities. I'm using a symmetric key to encrypt the messages. 

Right now I've stumbled upon a question. Is it enough to encrypt then sign when using symmetric-key encryption? The signature process is based on an asymmetric key pair. I think that by encrypting the message the content will be hidden and then if I sign it it will be authenticated but I feel like something is off. I'd like to hear someone else's opinion on this topic since I'm nothing but a beginner trying to learn.
Well, it would depend somewhat on what your security goals are, but signing the message would enable the receiver to verify integrity: that the ciphertext that it got is precisely the ciphertext that the sender sent (at some point; you still may need to worry about replay).

However, you're assuming that you have a shared symmetric key to encrypt; is there a specific reason you don't use that to also perform integrity (either by using a combined mode operation, such as AES-GCM, or generating a Message Authentication Code using other key bits that you shared).  The one thing that using a signature buys you is the ability to prove to a third party that the message is authentic (and not something the receiver made up); is that important to you?