int datatype initialization : Array vs Regular

Question

class returntest
{
    public static void main(String...args)
    {
        int a;
        System.out.println(a); //Line 1

        int b[] = new int[10];
        System.out.println(b[1]); //Line 2
    }
}

I get a compiler error (obviously) at Line 1 stating that the variable may not have been initialized.

I know all int array elements are initialized to 0 by default (so Line 2 compiles successfully) but my question is why cant compiler apply the same logic (of setting to 0 for all ints) to regular (non-array) int variables.

Is there any limitation that prohibits the compiler from doing that ?

Please have a look into stackoverflow.com/questions/13511702/int-array-initialization — Prabhaker A
– Prabhaker A, Commented Aug 31, 2013 at 7:17
In future, please format your code appropriately when you ask a question - see tinyurl.com/so-list. It also helps if you use conventional names (unlike returntest) even for dummy code - it's just less distracting that way. — Jon Skeet
– Jon Skeet, Commented Aug 31, 2013 at 7:24

Michael Petrotta · Accepted Answer · 2013-08-31 07:24:52Z

4

Local variables defined in a block of statements always must be initialized before use.

But member variables, those defined directly in the body of a class, are automatically initialized to 0 when the object is created.

Useful thread here.

edited Aug 31, 2013 at 7:24

Michael Petrotta

61.1k27 gold badges153 silver badges181 bronze badges

answered Aug 31, 2013 at 7:15

Naveen Kumar Alone

7,6985 gold badges40 silver badges59 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Rahul Tripathi · Accepted Answer · 2013-08-31 07:15:11Z

2

From here:-

Local variables are slightly different; the compiler never assigns a default value to an uninitialized local variable. If you cannot initialize your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialized local variable will result in a compile-time error.

answered Aug 31, 2013 at 7:15

Rahul Tripathi

173k33 gold badges292 silver badges341 bronze badges

Comments

Joop Eggen · Accepted Answer · 2013-08-31 07:20:30Z

0

This was a language design decision.

Having a default initialisation for local variables could hide errors. The usage of a local variable implies you want to set it first. Simple cases of forgetting to set it, or setting it only in if then are captured.

answered Aug 31, 2013 at 7:20

Joop Eggen

110k8 gold badges89 silver badges142 bronze badges

Comments

bNd · Accepted Answer · 2013-08-31 07:24:21Z

0

When variable scope is local then you must initialized local variable.

When you declare any local/block variable, they didn’t get the default values. They must assigned some value before accessing it other wise compiler will throw an error.

As you see in your code

int a; //Gives error because not assigned any value

When you allocate resources for a local variable, Java doesn't write a value into the memory. The reason you get an error is because Java makes sure you give it a value before you use it. Sun realized that this can be a difficult problem to diagnose in C code, because you don't get help from the compiler, so they decided to check it at compile time.

Refer this link

edited Aug 31, 2013 at 7:24

answered Aug 31, 2013 at 7:13

bNd

7,6507 gold badges43 silver badges73 bronze badges

Collectives™ on Stack Overflow

int datatype initialization : Array vs Regular

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related