Accessing outer class variable/member in inner class safe practice?

Question

In java for example, I declared and initialized a JButton in outer class and inside the inner class, I decided to make it hidden in some cases, is this a safe programming practice?

Answer 1

The whole purpose of inner classes is that they have access to the outside class that wraps around that inner class.

So the generic answer is: you are simply making use of a concept that the Java language provides to you. From that point - sure, go for it.

But beyond that, keep in mind the SOLID principles, like the single responsibility principle. Meaning: when there are good reasons for an inner class to use outer things (to get its "job" done) - then yes, go for it.

Then: to a certain degree, this is a style question. Inner classes were "famous" in the early years of Java, for example to implement specific listener interfaces. Nowadays they are "less common" - many people prefer "one class per file" and try to avoid nesting classes.

You see, a inner class is directly coupled to its outer class, so you reduce your ability to re-use that inner part. So you should only use inner classes for things that really conceptually belong "into" your that outer class.

In other words:

• don't use a concept just because you can - but because using this concept allows you to "best" implement a specific requirement
• nobody here can tell you what "works" for your project. Make sure to align with your peers on the style that people agree on, and use that.