Collection.sort

有时候我们需要集合中的元素按照某种规则排列，这个时候就需要用到Comparator.
示例代码:

//以map示例，其实就是把map转换成list排序之后再装入LinkedHashMapMap<String,String> map = new HashMap<String,String>();map.put("a","1");map.put("b","2");List<Entry<String,String>> list = new ArrayList<Entry<String,String>>(map.entrySet());Collection.sort(list,new Comparator<Entry<String,String>>(){    //重写compare方法    public int compare(Entry<String,String> e1, Entry<String,String> e2){        //升序        return e1.getValue().compareTo(e2.getValue);        //降序        //return e2.getValue().compareTo(e1.getValue);    }});Map<String,String> result = new LinkedHashMap<String,String>();for(Entry<String,String> e : list){    result.put(e.getKey(),e.getValue);}