Where it is better to initialize field?

Question

Where it is better to initialize fields? In constructor (var.1) or on declaration (var.2)?

var. 1

public class UtilWebLoading {
private int data;
private Context context;

public UtilWebLoading(Context context) {
    this.context = context;
    data = 100;
}
...
}

var. 2

public class UtilWebLoading {
private int data = 100;
private Context context;

public UtilWebLoading(Context context) {
    this.context = context;
}
...
}

I think you should look for a better example e.g. a list member with no constructor parameters, because in this case there is no real choice, since example 2 is wrong. — Tudor, Jul 09 '12 at 13:19
possible duplicate of [Best Practice: Initialize class fields in constructor or at declaration?](http://stackoverflow.com/questions/24551/best-practice-initialize-class-fields-in-constructor-or-at-declaration) — Denys Séguret, Jul 09 '12 at 13:20

score 13 · Accepted Answer · answered Jul 09 '12 at 13:14

13

In var. 1 the context has been initiated, while in var. 2 it will be null! Use the first one.

answered Jul 09 '12 at 13:14

Carnal

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It won't run, but if he would place Context context on top of the Util in var 2. it would run, but with null value. – Carnal Jul 09 '12 at 13:29

score 4 · Answer 2 · answered Jul 09 '12 at 13:17

I personally prefer to initialize fields when I have sufficient context to do so. For example, if I have a List field I usually initialize it upon declaration (unless the class requires the user to pass an implementation of their choosing), but if I have an array that requires a size to be passed, I'm forced to wait for a constructor call.

Hence, in your case, the second snippet does not have enough context to initialize Util at declaration, because no valid Context member exists.

Where it is better to initialize field?

2 Answers2