1. the three parts of for loop
part I: initialization
part II: governing condition (for the loop to continue)
part III: post condition, i.e. what's going to happen after each loop
however, ++i requires that increase i by 1 before entering a loop, this conflict with part III definition.

2. because the way float(double) numbers are represented in computer, u will find some floating point computing "wrong": 0.5 + 0.2 /= 0.7.

3. if (even==true)
in C, you can write if (var = somevalue), which will assign somevalue to var and return true, but in java, this is not allowed.

4. even = number%2==0 <==> even = (number%2==0)
sequence of actions taken by computer:
(1) computer number%2
(2) compare the previous result and 0 and return comparision result as a boolean value
(3) assign the boolean value to even.

其实每个问题都有想对应的理论（或者说术语）来解释的， 不过我一时间都想不起来是什么， 希望你大概明白吧。
如有纰漏，敬请各位更正。