Should I initialize variable within constructor or outside constructor [duplicate]

When I use Java based on my C++ knowledge, I love to initialize variable using the following way.

public class ME {
    private int i;

    public ME() {
         this.i = 100;
    }
}

After some time, I change the habit to

public class ME {
    private int i = 100;

    public ME() {
    }
}

I came across others source code, some are using 1st convention, others are using 2nd convention.

May I know which convention do you all recommend, and why?