Thinking in java学习笔记之map的应用

 Random rand = new Random(47);

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

	   for(int i=0;i<10000;i++){

		   int r= rand.nextInt(20);

		   Integer freq =m.get(r);

		   m.put(r,freq==null?1:freq+1);

	   }

	   System.out.println(m);

/*

输出

{0=481, 1=502, 2=489, 3=508, 4=481, 5=503, 6=519, 7=471, 8=468, 9=549, 10=513, 11=531, 12=521, 13=506, 14=477, 15=497, 16=533, 17=509, 18=478, 19=464}

*/