Does Java syntax for iteration across arrays allocate memory?

Question

I am programming for a memory-constrained device. Hence, I want to avoid allocating any memory.

Obviously, iterating across sets, lists, etc will allocate an iterator and thus allocate memory. So this should be avoided.

Does the native java syntax for iterating across arrays allocate memory?

Object[] array = getArray()
for(Object elem: array){
  //do something
}

(I suppose I could always use the old-fashioned for loop with an index variable.)

I wasn't aware that one could disable the JVM garbage-collector. How does anything work in that scenario? — Oliver Charlesworth
– Oliver Charlesworth, Commented Jan 15, 2012 at 14:34
You're right, the GC is not completely disabled - we just want to avoid having it run, so I prefer to view it as such. — jhourback
– jhourback, Commented Jan 15, 2012 at 14:38
Refer to this question. stackoverflow.com/questions/5369730/java-for-loop-differences — Kumar Bibek
– Kumar Bibek, Commented Jan 15, 2012 at 14:43

nikkatsa · Accepted Answer · 2020-03-07 18:41:36Z

6

Nope. In all compilers that I have checked this is implemented by a for loop (0..array.lengh-1).

Note that Java arrays do not implement Iterable. This can be seen, for instance, by the following code:

Object[] arr = new String[100];
Iterable<?> iter = arr;  // Error: 'Type mismatch: 
                         //         cannot convert from Object[] to Iterable<?>'

[UPDATE]

And here is the definite source: https://docs.oracle.com/javase/specs/jls/se13/html/jls-14.html#jls-14.14.2

A for loop such as

for ( VariableModifiersopt Type Identifier: Expression) Statement

has the following meaning when Expression is an array of type T[]:

T[] a = Expression;
for (int i = 0; i < a.length; i++) {
       VariableModifiersopt Type Identifier = a[i];
       Statement
}

edited Mar 7, 2020 at 18:41

nikkatsa

1,8134 gold badges28 silver badges43 bronze badges

answered Jan 15, 2012 at 14:35

Itay Maman

30.8k12 gold badges93 silver badges124 bronze badges

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

Comments

Óscar López · Accepted Answer · 2012-01-15 14:38:19Z

2

It doesn't allocate new memory. The following foreach loop:

for (type var : array) {
    body-of-loop
}

Is equivalent to this:

for (int i = 0; i < array.length; i++) { 
    type var = array[i];
    body-of-loop
}

As you can see, no additional memory allocation is being made.

answered Jan 15, 2012 at 14:38

Óscar López

237k38 gold badges321 silver badges391 bronze badges

2 Comments

jb. Over a year ago

To be specific it takes some stak space for type var = array[i] ;)

Óscar López Over a year ago

Well, int i and type var do allocate a bit of stack memory (and a constant value), but no additional heap memory is allocated.

Collectives™ on Stack Overflow

Does Java syntax for iteration across arrays allocate memory?

2 Answers 2

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related