Constructor vs Non-Static Init block

Question

I've just learned about init block. I know both(constructor & non-static init block) can be used to initialise members of a class . So, I wanted to know which out of the two is better/more_useful for initialisation of members of a class and what is the reason for it. I have read Use of Initializers vs Constructors in Java but I don't think it answer my question(if had miss anything in this question then please mention it and explain it in easy words.)

Note: I am asking for initialisation of non-static members only.

Thankyou in Advance

Also this one: http://stackoverflow.com/questions/1355810/how-is-an-instance-initializer-different-from-a-constructor — Tunaki, Jun 10 '16 at 07:20
@Andy please help me to point out the line which answer my question bcz I am unable to find it — , Jun 10 '16 at 07:24
Can I point out "the line"? No - it is not a simple question, and the answers (in both the duplicate I have marked and that suggested by Tunaki) are correspondingly long. The best way I can summarize it is "use a constructor by default; only think to use an instance initializer if you find that you really need it". — Andy Turner, Jun 10 '16 at 07:31
@Tunaki thanks for directing me to correct answer . Thankyou :) — , Jun 10 '16 at 07:31

score 0 · Answer 1 · edited Jun 10 '16 at 07:58

0

If you want to initialize a particular thing lots of times then go for non static else go for constructor. For example

public class test{
    int i;//you want to initialize i to 100 when any object is created then go for non static
    {
        i=10;
    }
    test(){}
    test(int x)
    {
    }
    test(String y)
    {
    }

    public static void main(String args[])
    {
        test t=new test();// i will be 10 during this
        // 
        test t1=new test("hello");// if you call this constructor also i will be 10
        //
        test t2=new test(10);// even if you call this constructor i will be 10
    }

If you wanted to initialize in constructors then there will be code duplication

public class test{
    int i;//there will be code duplication if you initialize in constructors


    test(){i=10;}
    test(int x)
    {
        i=10;
    }
    test(String y)
    {
        i=10;
    }

    public static void main(String args[])
    {
        test t=new test();// i will be 10 during this
        // 
        test t1=new test("hello");// if you call this constructor also i will be 10
        //
        test t2=new test(10);// even if you call this constructor i will be 10
    }

Again it will be a problem if you want to initialize i to 100 then you have to change in all constructors but if you go for non static way then you have to change in only one place

edited Jun 10 '16 at 07:58

Draken

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answered Jun 10 '16 at 07:16

SpringLearner

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by "lot of things " do you mean every single object that I create of my class and do we have any other reason to go for init block ? – Jun 10 '16 at 07:21
@PrayagSharma Please read the updated answer – SpringLearner Jun 10 '16 at 07:24
I don't quite agree to "there will be code-duplication": a constructor can call other constructors. – TmTron Jun 10 '16 at 07:27
@TmTron As per the example above, isnt i=10 duplicated ? – SpringLearner Jun 10 '16 at 07:28
in your code example it is. But it would be much better to call `test();` instead: e.g. in the `test(int x)` constructor – TmTron Jun 10 '16 at 07:31
1

@TmTron What if different constructor does different functions e.g `test(){i=10;sysout("no arg constructor is only called")} test(int x){i=10;sysout("int arg constructor is only called");` – SpringLearner Jun 10 '16 at 07:33
yes. then it would make sense - you should update your answer to reflect this (also you mix up 10 and 100 in your example). Anyway, even it his case, there are [alternatives](http://stackoverflow.com/a/3386148/6287240), which should be mentioned. – TmTron Jun 10 '16 at 07:46

Constructor vs Non-Static Init block

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