Completing work in constructor VS using an initializer

Question

From what I have seen in other peoples code, there appears to be two ways common ways in creating an object and "readying" it to be used.

Method 1: Ready the object in the constructor:

public class SomeClass {
  int setting;

  public SomeClass(int setting) {
    this.setting = setting;
  }
}

Method 2: Create the Object then "ready" it inside an initialize method such as:

public class SomeClass {
  int setting;

  public SomeClass(int setting) {

  }

  public void init(int setting) {
    this.setting = setting;
  }
}

Is there any specific reason to use either method over another?

There is no specification to used either, it is totally base on your requirement of how to initialize variable. — Yagnesh Agola
– Yagnesh Agola, Commented Dec 30, 2013 at 11:02

Jon Skeet · Accepted Answer · 2013-12-30 10:54:18Z

One reason for using the constructor is that you can make the field final - immutability isn't an option if you the constructed object isn't fully initialized. Personally I prefer to write code so that by the time an object is available, it's really ready to use - rather than having life-cycles of "construct, initialize, use".

On the other hand, doing a lot of work in a constructor is also generally frowned upon - partly because during construction you're potentially in an odd state as any subclasses won't have run their constructor bodies yet, so calling overridden methods in constructors is a bad idea.

Another alternative is to have a static method which does most of the actual work, and then delegates to a constructor just passing in field values. Factory methods like this have additional benefits such as the ability to return null where appropriate (rare, but it happens) or reuse existing objects.

Charles Stevens · Accepted Answer · 2013-12-30 10:59:48Z

2

As per the codes in your question: Whenver you use setting and want it to be initialized you need to use the argument constructor SomeClass(int setting) like:

  SomeClass someClass=new SomeClass(12);

And in the second case you need to call the method by passing the argument to get it initialised as in:

   SomeClass someClass=new SomeClass(6);
   someClass.init(6);

This depends on your requirement ,however initializing a variable using a constructor is mostly preferred.

answered Dec 30, 2013 at 10:59

Charles Stevens

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Community · Accepted Answer · 2017-05-23 11:56:47Z

2

Yes, as these 2 approaches give different behaviour, hence one may be preffered over the other:

In 2nd approach, class members are automatically initialized by the compiler using the default constructor, unless you call init method and set the values to your required initial values.

So, setting will be 0 by default when the object is created. Now, if you do not call init() on the newly created object and use it in your program, this may lead to undesirable behaviour. This is the reason the constructor approach is preffered.

However, placing too much code in constructor may lead to poor responsiveness, and also produces undesired results in case of inheritence. For such reasons, First approach is not preffered in general.

edited May 23, 2017 at 11:56

CommunityBot

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answered Dec 30, 2013 at 11:11

Infinite Recursion

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