实例化对象 - Object dog = new Dog();

Object dog = new Dog();
Dog dog = new Dog();
Dog<String,Integer> dog = new Dog<String,Integer>();//泛型，实例化的时候加，编译前就可以判断有没有错误
ArrayList<String> doglist = new ArrayList<String>();//泛型，实例化的时候加，编译前就可以判断有没有错误

Map<String,Integer> map = new HashMap<>();
        map.put("Tom",87);
        map.put("Jerry",87);
        //泛型的嵌套
        Set<Map.Entry<String,Integer>> entry = map.entrySet();
        Iterator<Map.Entry<String, Integer>> iterator = entry.iterator();
        while(iterator.hasNext()){
            Map.Entry<String, Integer> e = iterator.next();
            String key = e.getKey();
            Integer value = e.getValue();
            System.out.println(key + "----" + value);
        }

jdk7写法：前面加<String,Integer>，后面<>