Java - Data structure - Map
Hashtable Key and Value date format Can not be null Sync-ed HashMap Key and Value date format Can be null Non sync so will be faster Methods : put remove (will return reomved item of null) get (by Key) keySet (return all Keys) Need to using iterator to loop the elements eg: Iterator<Integer> itr = hashtable.keySet().iterator(); while (itr.hasNext()) { Integer key = itr.next(); String value = hashtable.get(key); System. out .println( "Key" + key + " ,Value = " + value); } Or for (Map.Entry<String,String> m : hsMap.entrySet()){ System. out .println(m.getKey() + m.getValue()); } Eg : map and stream to find the max value Map < Integer , Integer > map = new HashMap < > ( ) ; for ( int i = 0 ; i < nums . length ; i ++ ) { //3 if ( map . putIfAbsent ( nums [ i ] , 1 ) != null ) { // ture = first time, int count = map . get ( nums [ i ] ) ; ...