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hammerguard
hammergua..

HashMap: getKey()

in Programming Questions  •  10 months ago  
Is there a way to return the key for a HashMap as an integer? I used integers as the key and I'm trying to get integers back when I call getKey() but it returns objects.

Replies(5)

hammerguard
hammergua..

Re: HashMap: getKey()

10 months ago
I think this gets it done...

int eger = Integer.parseInt(data.getKey().toString());

Get the key, convert to string, then convert to int.
andreas.schlegel
andreas.s..

Re: HashMap: getKey()

10 months ago
Have you tried generics?

Copy code
  2. import java.util.*;
  3. import java.util.Map.Entry;

  5. Map<Integer, String> m = new HashMap<Integer, String>();

  7. m.put(1,"one");
  8. m.put(2,"two");
  9. m.put(3,"three");

  11. for (Entry<Integer,String> entry : m.entrySet()) {
  12.     int k = entry.getKey();    
  13.     String v = entry.getValue();
  14.     println(k+" is "+v);
  15. }

hammerguard
hammergua..

Re: HashMap: getKey()

10 months ago
Ok, I ran across another problem and I tested the same thing in your equation just to see if it would make a difference. How can I remove a value/key from the HashMap within a loop without getting this "ConcurrentModificationException"?
Copy code
  1. import java.util.*;
  2. import java.util.Map.Entry;

  4. Map<Integer, String> m = new HashMap<Integer, String>();
  5. m.put(1, "one");
  6. m.put(2, "two");
  7. m.put(3, "three");

  9. for (Entry<Integer,String> entry : m.entrySet()) {
  10.   int k = entry.getKey();   
  11.   String v = entry.getValue();
  12.   println(k+" is "+v);
  13.   m.remove(k);
  14. }
andreas.schlegel
andreas.s..

Re: HashMap: getKey()

10 months ago
In this case you can use an iterator instead of a foreach loop. An iterator allows to remove elements while cycling through the entryset whereas a foreach loop doesn't. 


Copy code
  2. import java.util.*;
  3. import java.util.Map.Entry;

  5. Map<Integer, String> m = new HashMap<Integer, String>();

  7. m.put(1,"one");

  9. m.put(2,"two");

  11. m.put(3,"three");

  13. println( "size of map (start) : " + m.size() );

  15. Iterator<Entry<Integer,String>> iter = m.entrySet().iterator();

  17. while (iter.hasNext()) {
  18.     Entry<Integer,String> entry = iter.next();
  19.     int k = entry.getKey();    
  20.     String v = entry.getValue();
  21.     println(k+" is "+v);
  22.     iter.remove();
  23. }

  25. println( "size of map (end)  : " + m.size() );
hammerguard
hammergua..

Re: HashMap: getKey()

10 months ago
Thank you very much good sir.
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