"main" java.lang.OutOfMemoryError in Hashtable sorting and reversing -

i trying sort arraylist of hashtable (arraylist>). hastable has 3345588 entries. when tried sort , assign reverse order in hastable found

  exception in thread "main" java.lang.outofmemoryerror       @ java.util.hashtable.newentry(hashtable.java:91)      @ java.util.hashtable.put(hashtable.java:766) 

my code below

public static hashtable<string, integer> sortvalue(         hashtable<string, integer> t) {     // transfer list , sort     arraylist<map.entry<string, integer>> l = new arraylist<entry<string, integer>>(             t.entryset());     hashtable<string, integer> f = new hashtable<string, integer>();     collections.sort(l, new comparator<map.entry<string, integer>>() {         public int compare(map.entry<string, integer> o1,                 map.entry<string, integer> o2) {             return o1.getvalue().compareto(o2.getvalue());         }     });     // create new normalized hashtable index started 1     // frequent key     int = 1;     (int = l.size(); > 0; i--) {         f.put(l.get(i - 1).getkey(), a);// getting error here         a++;     }     // system.out.println(l);      return f; } 

you can try increase vm memory when running program. can read here vm memory setting how in details. sample:

java -xms1024m -xmx4096m com.sample.helloworld