Hexo

public class PokerGame2 { //只要牌的对象和只能对应就好了,不用treemap static HashMap<Integer,String> poker=new HashMap<>(); static ArrayList<Integer> list=new ArrayList<>(); static { String [] colors={"♦","♣","♥","♠"}; String []...

public class CollectionsDemo1 { public static void main(String[] args) { //collections是集合的工具类,不是集合 /* public static <T> boolean addAll(Collection<T> c,T...element) 批量添加元素 public static void shuffle(List<?> list) 打乱list集合元素的顺序 */ //1.创建集合 ArrayList<String> list = new ArrayList<>(); //2.批量添加元素 Collections.addAll(list, "haha", "xiangxiang", "baby",...

public class test1 { public static void main(String[] args) { //随机点名器 ArrayList<String> list=new ArrayList<>(); Collections.addAll(list,"xiangxiang","baby","haha","xixi","nono","yesyes"); Random r=new Random(); int index=r.nextInt(list.size()); String name=list.get(index); System.out.println(name); //或者是 Collections.shuffle(list); ...

public class ArgsDemo1 { public static void main(String[] args) { //可变参数 //方法形参个数可以改变 //格式:数据类型...变量名 //底层是一个数组 //小细节: //1.一个方法的形参列表,只能有一个可变参数 //2.如果方法的形参有多个,那么可变参数必须写在最后面 int sum=getSum(1,2,3,4,5,6,7,8,9,10); System.out.println(sum); } public static int getSum(int...a){ int sum=0; for (int i : a) { sum+=i; } return sum; ...

public class TreeMapDemo1 { public static void main(String[] args) { //integer,double 等默认情况都是升序排列 //String 默认情况是按照首字母的升序排列 TreeMap<Integer,String> tm1=new TreeMap<>(/*new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o1-o2;//根据商品价格升序排列 } }*/); tm1.put(1,"haha"); ...

public class HashMapTest1 { public static void main(String[] args) { //创建对象 //年龄,名字相同认为是同一个人(要重写hashCode和equals方法) HashMap<Student,String> hm=new HashMap<>(); Student s1=new Student("zhangsan",23); Student s2=new Student("lisi",24); Student s3=new Student("wangwu",25); Student s4=new Student("wangwu",25); hm.put(s1,"北京"); ...

public class MapDemo1 { public static void main(String[] args) { /* V put(K key, V value)//添加元素 V remove(Object key)//根据键删除键值对元素 void clear()//移除所有的键值对元素 boolean containsKey(Object key)//判断集合是否包含指定的键 boolean containsValue(Object value)//判断集合是否包含指定的值 boolean isEmpty()//判断集合是否为空 int size()//集合的长度，也就是集合中键值对的个数 */ //创建集合对象 Map<String,String> map=new HashMap<>(); //1.添加元素 ...

创建student的对象,并按方法一实现Comparable接口 public class Student implements Comparable<Student> { private String name; private int age; public Student() { } public Student(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; ...

public class SetDemo1 { public static void main(String[] args) { Set<String> set=new HashSet<>(); set.add("haha"); set.add("xiangxiang"); set.add("baby"); //1. Iterator<String> it = set.iterator(); while(it.hasNext()){ String s = it.next(); System.out.println(s); } //2. for(String s:set){ ...

public class GenericsDemo1 { public static void main(String[] args) { /* 泛型不具备继承性,但是数据具备继承性 */ ArrayList<Ye> list1 = new ArrayList<>(); ArrayList<Fu> list2 = new ArrayList<>(); ArrayList<Zi> list3 = new ArrayList<>(); method(list1); //method(list2);//报错 //method(list3);//报错 list1.add(new Ye());//可以 list1.add(new Fu());//可以 list1.add(new...