Java基础学习笔记【08】泛型限定、泛型操作

public static void up(List<? extends Number> l){ //方法的具体实现 }

public static void down(List<? super Number> l){ //方法的具体实现  ｝

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List<Integer> l1 = new ArrayList<Integer>(); 

List l2 = l1;

public static <T>List<T> asList(T ... t){}

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int[] arr = {1,2,3};  

List<Integer> l1 = Arrays.asList(arr);//ERROR  

List<int[]> l2 = Arrays.asList(arr);//YES    

Integer[] arr1 = arr;//ERROR  

Integer[] arr1 = {1,2,3};  

List<Integer> l3 = Arrays.asList(arr1);    

List <----> 数组  

List-->数组: Collection接口里的 Object[] toArray();   

List l = new ArrayList();     

l.add(1);  

l.add("a");  

l.add(false);

Object[] arr= l.toArray();

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List list = new ArrayList();     

String ele = (String)set.get(0);  

List<String> list = new ArrayList<String>();

String ele = set.get(0);

String ele = (String)set.get(0);

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Map<String,Date> map = new HashMap<String,Date>();    

map.put("A",new Date());   

Set<Map.Entry<String,Date>> entrys = map.entrySet();   //取出Map里所有Entry对象

Iterator<Map.Entry<String,Date>> it = entrys.iterator();//使用迭代器

//迭代出每一个Entry对象  

while(it.hasNext())    {

Map.Entry<String,Date> entry = it.next();     //取出每个entry里的 key和 value

String key = entry.getKey();

Date value = entry.getValue();    }  //show(new HashMap<>());

public static <T> List<T> asList(T ... t){     }

static Class<?> forName(String className)