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Index › Programming Questions & Help › Syntax Questions › Hash Map: Increase one value by 1
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Hash Map: Increase one value by 1 (Read 1543 times)
Chrisir
Hash Map: Increase one value by 1
Mar 13th, 2010, 3:51pm  
Hello,

I have a list of String-values list.
I have a Hash Map hm.
When the String list[i] is not in hm, hm gets a new entry called list[i], value 1.  
When list[i] is already in hm: In hm I want to increase the value of list[i] that appears in hm.
But I can't get the value from hm...

Any help appreciated!  Cry

Chrisir  Wink


       if (hm.containsKey(list[i])) {
         Map.Entry me = (Map.Entry)hm.get(list[i]) ; // i.next();
         int OldValue  =int (me.getValue());
         hm.put(list[i], OldValue+1);
       }
       else {
         hm.put(list[i], 1);          
       }
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PhiLho 
Re: Hash Map: Increase one value by 1
Reply #1 - Mar 14th, 2010, 12:29am  
Code:
HashMap hm = new HashMap();
String[] list = { "a", "b", "c", "a", "c", "a", "b", "a", "b" };
for (int i = 0; i < list.length; i++)
{
  Integer val = (Integer) hm.get(list[i]);
  if (val == null)
  {
    hm.put(list[i], 1);
  }
  else
  {
    hm.put(list[i], val + 1);
  }
}
println(hm);

I use a bit of "magic" of Java 1.5, which is able to automatically convert, when needed, Integer to int and back (auto-boxing).
Note also that instead of checking if a key is there then getting it, I just get it and see if I have a result: it is simpler and faster.
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WWW  
Chrisir
Re: Hash Map: Increase one value by 1
Reply #2 - Mar 15th, 2010, 2:30am  
Hello!

Oh, that helped me a lot.

That could easily be added to the help-section of HashMap.

Greetings, Chrisir    Wink  



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Chrisir
Re: Hash Map: Increase one value by 1
Reply #3 - Mar 17th, 2010, 2:01am  

Hello,

I have an additional question.

How much can a HashMap take?

Let's say 400'000 entries with each 9 Letters in the key and value between -9000 and +9000?

What happens when I put too many entries in?

Greetings, Chris    Wink
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koogy
Re: Hash Map: Increase one value by 1
Reply #4 - Mar 17th, 2010, 2:20am  
should be ok, is limited by your memory more than anything in the code.
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PhiLho 
Re: Hash Map: Increase one value by 1
Reply #5 - Mar 17th, 2010, 4:06am  
The question is interesting. koogy's answer is accurate, but I was curious.
Look at the source of HashMap (available with the JDK), I see:
static final int MAXIMUM_CAPACITY = 1 << 30;
That's 1,073,741,824...
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Chrisir
Re: Hash Map: Increase one value by 1
Reply #6 - Mar 17th, 2010, 5:13am  


should be ok (for now Roll Eyes)
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