Depends on your motivation, if you're looking to learn a language for the sake of employability then yes Java is definitely worth learning.
On the other hand if you're interested in learning something that will make you an overall better programmer it's best to learn something different than what you're familiar with (most likely Java isn't much different than what you've used), e.g. learning C (if you haven't written lower level code) or a functional language (if you've never used one) will grow you much more as a developer than adding yet another generic object-oriented language to your skillset.
On the other hand if you're interested in learning something that will make you an overall better programmer it's best to learn something different than what you're familiar with (most likely Java isn't much different than what you've used), e.g. learning C (if you haven't written lower level code) or a functional language (if you've never used one) will grow you much more as a developer than adding yet another generic object-oriented language to your skillset.