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可变参数：
就是一种特殊形参，定义在方法，构造器的形参列表中，格式是：数据类型...参数名称
可变参数的好处：
灵活的接收数据
特点：可以不传数据给它，可以传一个数据或者多个数据给它，也可以传一个数组给它
可变参数的注意事项：
可变参数在方法内部就是一个数组
一个形参列表中的可变参数只有一个
可变参数必须在形参列表的最后面
public class test {public static void main(String[] args) {ttt();//可以不传数据ttt(1);//可以传一个数据ttt(1,2,3);//可以传多个数据ttt(new int[]{1,2,3});//可以传一个数组}public static void ttt(int...nums){//可变参数在方法内部是一个数组System.out.println(Arrays.toString(nums));}//只能有一个可变参数，且必须在形参列表的最后public static void ppp(int age,int...s){}
}
Collections类：
是一个用来操作集合的工具类
public static <T> boolean addAll(Collection<? super T> c, T... elements)
Adds all of the specified elements to the specified collection. Elements to be added may be specified individually or as an array.
往集合中批量添加数据
public static void shuffle(List<?> list)
Randomly permutes the specified list using a default source of randomness.
打乱List集合中的元素顺序
void sort(List<T> list)
对List集合中的元素进行升序排序
public static <T> void sort(List<T> list, Comparator<? super T> c)
Sorts the specified list according to the order induced by the specified comparator.
对List集合中的元素，按照比较器对象指定的规则进行排序
public class test {public static void main(String[] args) {//1 addAllArrayList<String>list=new ArrayList<>();Collections.addAll(list,"java1","java2","java3");System.out.println(list);//2:shuffleCollections.shuffle(list);System.out.println(list);//[java2, java3, java1]//sort,默认升序Collections.sort(list);System.out.println(list);//[java1, java2, java3]//sort排序自定义对象ArrayList<Student>list1=new ArrayList<>();list1.add(new Student("aa",10));list1.add(new Student("bb",90));list1.add(new Student("cc",22));Collections.sort(list1, new Comparator<Student>() {@Overridepublic int compare(Student o1, Student o2) {return o1.getAge()-o2.getAge();//按照年龄升序}});Collections.sort(list1,(o1,o2)->o1.getAge()-o2.getAge());System.out.println(list1);}
}public class test {public static void main(String[] args) {//1 addAllArrayList<String>list=new ArrayList<>();Collections.addAll(list,"java1","java2","java3");System.out.println(list);//2:shuffleCollections.shuffle(list);System.out.println(list);//[java2, java3, java1]//sort,默认升序Collections.sort(list);System.out.println(list);//[java1, java2, java3]//sort排序自定义对象ArrayList<Student>list1=new ArrayList<>();list1.add(new Student("aa",10));list1.add(new Student("bb",90));list1.add(new Student("cc",22));Collections.sort(list1, new Comparator<Student>() {@Overridepublic int compare(Student o1, Student o2) {return o1.getAge()-o2.getAge();//按照年龄升序}});Collections.sort(list1,(o1,o2)->o1.getAge()-o2.getAge());System.out.println(list1);}
}以下是一个简单的游戏：
牌类：
public class Card {private String number;private String color;private int size;public Card() {}public Card(String number, String color, int size) {this.number = number;this.color = color;this.size = size;//牌的大小}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public int getSize() {return size;}public void setSize(int size) {this.size = size;}@Overridepublic String toString() {return "Card{" +"number='" + number + '\'' +", color='" + color + '\'' +", size=" + size +'}';}
}
操作牌类
public class Room {private ArrayList<Card>list=new ArrayList<>();public Room() {String []numbers={"3","4","5","6","7","8","9","10","J","Q","K","A","2"};int size=0;String []colors={"方块","梅花","红桃","黑桃"};for (String number : numbers) {size++;for (String color : colors) {Card c=new Card(number,color,size);list.add(c);}}Card c1=new Card("","小王",size++);Card c2=new Card("","大王",size);Collections.addAll(list,c1,c2);System.out.println(list);}public void randomCard(){System.out.println("开始洗牌");Collections.shuffle(list);//System.out.println(list);}public void devoteCard(){ArrayList<Card>list1=new ArrayList<>();ArrayList<Card>list2=new ArrayList<>();ArrayList<Card>list3=new ArrayList<>();for (int i = 0; i < list.size()-3; i++) {//只发51张牌Card c=list.get(i);if(i%3==0){list1.add(c);}else if(i%3==1){list2.add(c);}else{list3.add(c);}}sortCard(list1);sortCard(list2);//对牌进行大小排序sortCard(list3);System.out.println(list1);System.out.println(list2);System.out.println(list3);System.out.println("底牌是");List<Card> LastCard= list.subList(list.size()-3,list.size());//包前不包后System.out.println(LastCard);}private void sortCard(ArrayList<Card> list2) {/*Collections.sort(list2, new Comparator<Card>() {@Overridepublic int compare(Card o1, Card o2) {return o1.getSize()-o2.getSize();}});}*/Collections.sort(list2, (o1, o2) -> o1.getSize() - o2.getSize());}
}
test:
public class test {public static void main(String[] args) {Room r=new Room();r.randomCard();ArrayList<Card>[]lists=new ArrayList[3];r.devoteCard();}
}
结果：
[Card{number='3', color='方块', size=1}, Card{number='3', color='梅花', size=1}, Card{number='3', color='红桃', size=1}, Card{number='3', color='黑桃', size=1}, Card{number='4', color='方块', size=2}, Card{number='4', color='梅花', size=2}, Card{number='4', color='红桃', size=2}, Card{number='4', color='黑桃', size=2}, Card{number='5', color='方块', size=3}, Card{number='5', color='梅花', size=3}, Card{number='5', color='红桃', size=3}, Card{number='5', color='黑桃', size=3}, Card{number='6', color='方块', size=4}, Card{number='6', color='梅花', size=4}, Card{number='6', color='红桃', size=4}, Card{number='6', color='黑桃', size=4}, Card{number='7', color='方块', size=5}, Card{number='7', color='梅花', size=5}, Card{number='7', color='红桃', size=5}, Card{number='7', color='黑桃', size=5}, Card{number='8', color='方块', size=6}, Card{number='8', color='梅花', size=6}, Card{number='8', color='红桃', size=6}, Card{number='8', color='黑桃', size=6}, Card{number='9', color='方块', size=7}, Card{number='9', color='梅花', size=7}, Card{number='9', color='红桃', size=7}, Card{number='9', color='黑桃', size=7}, Card{number='10', color='方块', size=8}, Card{number='10', color='梅花', size=8}, Card{number='10', color='红桃', size=8}, Card{number='10', color='黑桃', size=8}, Card{number='J', color='方块', size=9}, Card{number='J', color='梅花', size=9}, Card{number='J', color='红桃', size=9}, Card{number='J', color='黑桃', size=9}, Card{number='Q', color='方块', size=10}, Card{number='Q', color='梅花', size=10}, Card{number='Q', color='红桃', size=10}, Card{number='Q', color='黑桃', size=10}, Card{number='K', color='方块', size=11}, Card{number='K', color='梅花', size=11}, Card{number='K', color='红桃', size=11}, Card{number='K', color='黑桃', size=11}, Card{number='A', color='方块', size=12}, Card{number='A', color='梅花', size=12}, Card{number='A', color='红桃', size=12}, Card{number='A', color='黑桃', size=12}, Card{number='2', color='方块', size=13}, Card{number='2', color='梅花', size=13}, Card{number='2', color='红桃', size=13}, Card{number='2', color='黑桃', size=13}, Card{number='', color='小王', size=13}, Card{number='', color='大王', size=14}]
开始洗牌
[Card{number='3', color='方块', size=1}, Card{number='3', color='黑桃', size=1}, Card{number='4', color='黑桃', size=2}, Card{number='4', color='梅花', size=2}, Card{number='4', color='方块', size=2}, Card{number='6', color='方块', size=4}, Card{number='8', color='梅花', size=6}, Card{number='8', color='黑桃', size=6}, Card{number='9', color='梅花', size=7}, Card{number='10', color='黑桃', size=8}, Card{number='10', color='方块', size=8}, Card{number='J', color='红桃', size=9}, Card{number='J', color='梅花', size=9}, Card{number='J', color='黑桃', size=9}, Card{number='K', color='红桃', size=11}, Card{number='A', color='黑桃', size=12}, Card{number='2', color='黑桃', size=13}]
[Card{number='3', color='红桃', size=1}, Card{number='6', color='黑桃', size=4}, Card{number='6', color='红桃', size=4}, Card{number='7', color='方块', size=5}, Card{number='7', color='红桃', size=5}, Card{number='7', color='黑桃', size=5}, Card{number='10', color='梅花', size=8}, Card{number='J', color='方块', size=9}, Card{number='Q', color='黑桃', size=10}, Card{number='K', color='方块', size=11}, Card{number='K', color='梅花', size=11}, Card{number='K', color='黑桃', size=11}, Card{number='A', color='红桃', size=12}, Card{number='2', color='梅花', size=13}, Card{number='2', color='红桃', size=13}, Card{number='', color='小王', size=13}, Card{number='', color='大王', size=14}]
[Card{number='3', color='梅花', size=1}, Card{number='4', color='红桃', size=2}, Card{number='5', color='红桃', size=3}, Card{number='5', color='梅花', size=3}, Card{number='5', color='方块', size=3}, Card{number='5', color='黑桃', size=3}, Card{number='7', color='梅花', size=5}, Card{number='8', color='红桃', size=6}, Card{number='8', color='方块', size=6}, Card{number='9', color='黑桃', size=7}, Card{number='9', color='方块', size=7}, Card{number='9', color='红桃', size=7}, Card{number='10', color='红桃', size=8}, Card{number='Q', color='红桃', size=10}, Card{number='Q', color='梅花', size=10}, Card{number='Q', color='方块', size=10}, Card{number='2', color='方块', size=13}]
底牌是
[Card{number='A', color='梅花', size=12}, Card{number='6', color='梅花', size=4}, Card{number='A', color='方块', size=12}]