泛型 、entry词遍历方式、迭代器方式遍历

public class Fanxing<T> {//类的模板，类在编译时未确认
    private T a;
    private T b;
    public T add(){
        return a;
    }
    public T sub(){
        return b;
    }

    @Test
    public void fanxing(){
        List<String> list = new ArrayList<>();
        list.add("aa");
        String s = list.get(0);

        Map<Integer,String> map = new HashMap<>(); //泛型
        map.put(1, "张三丰");
        map.put(2, "周芷若");
        map.put(3, "汪峰");
        Set<Integer> set = map.keySet();
        for (Integer i : set) {
            String v = map.get(i);
            System.out.println(i + "  " +v);
        }
        //了解 entry词:表达map的键值  成对的
        Set<Map.Entry<Integer,String>> entries = map.entrySet();
        for (Map.Entry<Integer, String> entry : entries) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
        //迭代器方式遍历  早期
        Iterator<Integer> it = set.iterator();
        while(it.hasNext()){
            Integer k = it.next();
            String  v = map.get(k);
            System.out.println(k + " " +v);
        }
    }
}