I tried to make an independent copy of an array but couldnt get one. see i cannot copy it integer by integer using a for loop because of efficiency reasons. Is there any other way? This was my code:
int[] temp = new int[arr.length]; temp = arr; 
- 2What "efficiency reasons"? Did you actually test that this piece of code is a problem? Or are you just guessing?Joachim Sauer– Joachim Sauer2010-03-03 13:30:06 +00:00Commented Mar 3, 2010 at 13:30
- really strange efficiency reasons...Peter Perháč– Peter Perháč2010-03-03 13:35:20 +00:00Commented Mar 3, 2010 at 13:35
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5 Answers
Look at System.arraycopy() method. Like,
int[] b = new int[a.length]; System.arraycopy(a, 0, b, 0, a.length); 
Comments
Arrays.copyOf() creates a new copy of an existing array (optionally with a different length).
3 Comments
matt b
Note that this method is new in 1.6 and arguably easier to use than System.arraycopy()
Joachim Sauer
@matt: I no longer mention "new in Java 6", because Java 6 is old enough already (December 2006 is already some time in the past).
matt b
I didn't mean that as a reason to not use it - just a heads up for anyone who isn't familiar with it because they aren't using 1.6
Try using clone () method for this purpose. As I remember this is the only case where Josh Bloch in Effective Java recommended to use cloning.
int[] temp = arr.clone (); But arrayCopy is much faster. Sample performance test on array of 3,000,000 elements:
System.arrayCopy time: 8ms arr.clone() time: 29ms Arrays.copyOf() time: 49ms simple for-loop time: 75ms 3 Comments
Draemon
Nice stats, but it begs the question why he should "try using clone()"
Roman
because I first wrote about clone () and then made the test for the sake of interest :)
assylias
I can't reproduce the results, see my micro-benchmark which shows that the first 3 methods are equivalent. So I would favour the
Arrays.copyOf which was purposedly built for that task.Check out System.arraycopy(). It can copy arrays of any type and is a preffered(and optimized) way to copy arrays.
Comments
You can use System.arraycopy, but I doubt it will be much more efficient. The memory has to be copied anyways, so the only optimization possible is to copy bigger chunks of memory at once. But the size of a memory chunk copied at once is strongly limited by the processor/system-architecture.
1 Comment
Joachim Sauer
Especially for big arrays, that method can be quite a bit faster than a simple for-loop implementation.