hashmap的常用方法

HashMap<String, Integer> countMap = new HashMap<String, Integer>();
if(countMap.keySet().contains(a)){
    countMap.put(a, countMap.get(a)+1);
}else{
    countMap.put(a, 1);
}

Iterator it = mp.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry pairs = (Map.Entry)it.next();
    System.out.println(pairs.getKey() + " = " + pairs.getValue());
}

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

public static void (Map mp) {
    Iterator it = mp.entrySet().iterator();
    while (it.hasNext()) {
        Map.Entry pairs = (Map.Entry)it.next();
        System.out.println(pairs.getKey() + " = " + pairs.getValue());
        it.remove(); // avoids a ConcurrentModificationException
    }
}

class ValueComparator implements Comparator<String> {
    Map<String, Integer> base;
    public ValueComparator(Map<String, Integer> base) {
        this.base = base;
    }
    public int compare(String a, String b) {
        if (base.get(a) >= base.get(b)) {
            return -1;
        } else {
            return 1;
        } // returning 0 would merge keys
    }
}

HashMap<String, Integer> countMap = new HashMap<String, Integer>();
//add a lot of entries
countMap.put("a", 10);
countMap.put("b", 20);
ValueComparator vc =  new ValueComparator(countMap);
TreeMap<String,Integer> sortedMap = new TreeMap<String,Integer>(vc);
sortedMap.putAll(countMap);
printMap(sortedMap);