JavaSE进阶

public static void main(String[] args) {

HashMap<String,ArrayList<Citizen>> map = new HashMap<String,ArrayList<Citizen>>();

ArrayList<Citizen> list = new ArrayList<Citizen>();

list.add(new Citizen("刘恺威"));

list.add(new Citizen("杨幂"));

list.add(new Citizen("小糯米"));

map.put("刘恺威", list);

Set<Entry<String, ArrayList<Citizen>>> entrySet = map.entrySet();

Iterator<Entry<String, ArrayList<Citizen>>> iterator = entrySet.iterator();

while(iterator.hasNext()){

Entry<String, ArrayList<Citizen>> next = iterator.next();

String key = next.getKey();

ArrayList<Citizen> value = next.getValue();

System.out.println("户主："+key);

System.out.println("家庭成员："+value);

}

}

public static void main(String[] args) {

Fruit f = new Apple();//多态

//泛型没有多态

// ArrayList<Fruit> list = new ArrayList<Apple>();//泛型没有多态

ArrayList<? extends Fruit> list = new ArrayList<Apple>();//使用通配符可以

}

public class TestGenericPolymophism {

public static void main(String[] args) {

//泛型没有数组

// Tiger<String>[] as = new Tiger<String>[];

}

}

class Tiger<T>{

}

ArrayList源代码

public class ArrayList<E>  。。。{

    transient Object[] elementData;

    public boolean add(E e) {

        ensureCapacityInternal(size + 1);  // Increments modCount!!

        elementData[size++] = e;

        return true;

}

    public E get(int index) {

        rangeCheck(index);

        return elementData(index);

}

    E elementData(int index) {

        return (E) elementData[index];

    }

}