General Java Questions I

Conversely, if you never (or rarely) use the entire array, its a waste of space and

memory.

The following are benchmark test results of vector vs. array (ran on a 200 Mhz

Pentium w/ 96 Mbytes of memory and Windows95 ):

Allocating vector elements: 17910 milliseconds

Allocating array elements: 4220 milliseconds

Accessing Vector elements: 18130 milliseconds

Accessing array elements: 10110 milliseconds

One other reason for vectors being slower that I did not mention above is that vector

methods are synchronized, which creates a performance bottleneck.

Hope this helps

MSW

 Q: Would anyone know the performance issues regarding Vector s?

I am actually talking about resource pooling. I have objects that wait in a queue. It is a

vector that keeps growing, as the queue gets bigger.

Do Vectors have much performance hit? Is there a better way to implement vectors to

get the best out of them? Or am I better of creating a fixed size array?

Answer 1: 

If you just want a LIFO or LILO queue, you may be better off with 

LinkedList than with Vector, as then you ll never have to wait for the contents to be

copied.

Vectors perform pretty well, but if you know (even roughly) how big you re going to

need it to be, specifying that in the constructor call can help.

How sure are you that this will be a performance bottleneck? Premature optimisation

is the root of all evil...

The Vector class is thread safe. By that I mean that there is no way to corrupt the

internal representation of the data by accessing the vector from more than one

thread. However, it is still possible, very easy in fact, to use a vector in a way that is

not thread safe.

Consider this code:

for (int i = 0; i < vector.size(); i++) {

System.out.println(vector.elementAt(i));

}

It looks safe, but there s a subtle flaw... 

Answer 2: Suppose you start with a vector of ten elements. On the tenth iteration i will

have the value 9 and the test i < vector.size() will succeed. 

Now suppose the thread scheduler chooses this moment to pause the current thread

and let another thread run. This second thread removes an object from the vector.

Now when the first thread resumes, the vector has only nine elements and 9 is no

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