Java-替换位集

Question

In my code I am trying to get if a number exist in the hashmap or not. My code is following:

BitSet arp = new BitSet();

for i = 0 to 10 million

HashMap.get (i)

if number exist
arp.set(i , true)

else
arp.set(i , false)

After that from bitset I get if number i exist or not. However, I found this bitset operation is quite slow (tried with string = string + 0/1 also, more slower). Can anybody help me how to replace this operation with a faster one.

Answer 1

Your code is really difficult to read clearly, but I suspect you're just trying to set bits in the BitSet that are keys from your HashMap ?

In that case, your code should just be more or less

BitSet bits = new BitSet(10000000);
for (Integer k : map.keySet()) {
  bits.set(k);
}

Even if this wasn't what you meant, as a general rule, BitSet is blazing fast; I suspect it's the rest of your code that's slow.

Answer 2

If you provided your actual relevant code, we could have found some performance errors in the first place. But assuming your code is ok and you profiled your application to make sure that the BitSet operations are actually slow:

If you have enough memory space available, you can always just go for a boolean[] instead of a BitSet .

BitSet internally uses long[] to store the separate bits, so it's very good memory-wise, but can sometimes be a little bit too slow.