Should I initialize variable within constructor or outside constructor

I find the second style (declaration + initialization in one go) superior. Reasons:

• It makes it clear at a glance how the variable is initialized. Typically, when reading a program and coming across a variable, you'll first go to its declaration (often automatic in IDEs). With style 2, you see the default value right away. With style 1, you need to look at the constructor as well.
• If you have more than one constructor, you don't have to repeat the initializations (and you cannot forget them).

Of course, if the initialization value is different in different constructors (or even calculated in the constructor), you must do it in the constructor.

I have the practice (habit) of almost always initializing in the contructor for two reasons, one in my opinion it adds to readablitiy (cleaner), and two there is more logic control in the constructor than in one line. Even if initially the instance variable doesn't require logic, having it in the constructor gives more flexibility to add logic in the future if needed.

As to the concern mentioned above about multiple constructors, that's easily solved by having one no-arg constructor that initializes all the instance variables that are initilized the same for all constructors and then each constructor calls this() at the first line. That solves your reduncancy issues.