Collections
Collenctions overview and use
Overview of the Collections class
- Is a tool class for collection operations
Common methods of the Collections class
- public static <T extends Comparable<? super T>> void sort(List list): Sort the specified list in ascending order
- public static void reverse(List<?> list): Reverse the order of the elements in the specified list
- public static void shuffle(List<?> list): Randomly shuffle the specified list using the default random source
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/*
Collections类的概述
- 是针对集合操作的工具类
Collections类的常用方法
- public static <T extends Comparable<? super T>> void sort(List<T> list)：将指定的列表按升序排序
- public static void reverse(List<?> list)：反转指定列表中元素的顺序
- public static void shuffle(List<?> list)：使用默认的随机源随机排列指定的列表
*/
public class CollectionsDemo {
public static void main(String[] args) {
//创建List集合对象
List<Integer> list = new ArrayList<Integer>();
//添加元素
list.add(10);
list.add(20);
list.add(40);
list.add(60);
list.add(50);
// public static <T extends Comparable<? super T>> void sort(List<T> list)：将指定的列表按升序排序
Collections.sort(list);
/*运行结果：
[10, 20, 40, 50, 60]
*/
// public static void reverse(List<?> list)：反转指定列表中元素的顺序
Collections.reverse(list);
/*运行结果：反转列表中元素的顺序
[50, 60, 40, 20, 10]
*/
// public static void shuffle(List<?> list)：使用默认的随机源随机排列指定的列表
Collections.shuffle(list);
/*运行结果：随机排序 每次运行会出现不同的结果
[10, 60, 20, 50, 40]
*/
System.out.println(list);
}
}
Case: ArrayList stores and sorts student objects
Requirements: ArratLIst stores student objects, and uses Collections to sort ArrayList
Requirements: Sort by age from young to old, and when the age is the same, sort by name alphabetically
//定义学生类
public class Student {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public Student() {
super();
}
}
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
/*
案例：ArrayList存储学生对象并排序
需求：ArratLIst存储学生对象，使用Collections对ArrayList进行排序
要求：按照年龄从小到大的排序，年龄相同时，按照姓名的字母顺序排序
*/
public class ArrayListDemo {
public static void main(String[] args) {
//创建ArrayList集合对象
ArrayList<Student> array = new ArrayList<Student>();
//创建学生对象
Student s1 = new Student("小白", 12);
Student s2 = new Student("小黑", 11);
Student s3 = new Student("小蓝", 14);
Student s4 = new Student("小红", 15);
//把学生添加到集合中
array.add(s1);
array.add(s2);
array.add(s3);
array.add(s4);
//使用Collections对集合排序
//sort (List<T> list,Comparator<? super T>)
Collections.sort(array, new Comparator<Student>() {
@Override
public int compare(Student s1, Student s2) {
//按照年龄从小到大的排序
int num = s1.getAge() - s2.getAge();
//年龄相同时，按照姓名的字母顺序排序
int num2 = num == 0 ? s1.getName().compareTo(s2.getName()) : num;
return num2;
};
});
//遍历集合
for (Student s : array) {
System.out.println(s.getName() + "," + s.getAge());
}
}
}
operation result:
Case: Simulation of Fighting the Landlords
Requirements: Realize the shuffling, dealing and viewing of cards in the process of fighting landlords through programs
. Ideas:
- Create a card box, that is, define a collection object, and implement it with the ArrayList collection
- Put the cards in the box
- Shuffle, that is, to scatter the cards, using the shuffle() method of Collections
- Dealing cards, that is, traversing the collection, and dealing cards to three players
- Look at the cards, that is, the three players traverse their own cards respectively
import java.util.ArrayList;
import java.util.Collections;
/*
案例：模拟斗地主
需求：通过程序实现斗地主过程中的洗牌，发牌和看牌
思路：
1. 创建一个牌盒，也就是定义一个集合对象，用ArrayList集合实现
2. 往牌盒里面装牌
3. 洗牌，也就是把牌打撒，用Collections的shuffle()方法实现
4. 发牌，也就是遍历集合，给三个玩家发牌
5. 看牌，也就是三个玩家分别遍历自己的牌
*/
public class PoKerDemo {
public static void main(String[] args) {
// 1. 创建一个牌盒，也就是定义一个集合对象，用ArrayList集合实现
ArrayList<String> array = new ArrayList<String>();
// 2. 往牌盒里面装牌
/*
♦2，♦3，♦4。。。♦K,♦A
♣。。。
♥。。。
♠。。。
小王 大王
*/
//定义花色数组
String[] colors = {
"♦", "♣", "♥", "♠" };
//定义点数数组
String[] numbers = {
"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A" };
for (String color : colors) {
for (String num : numbers) {
array.add(color + num);
}
}
array.add("小王");
array.add("大王");
// System.out.println(array);
// 3. 洗牌，也就是把牌打撒，用Collections的shuffle()方法实现
Collections.shuffle(array);
// 4. 发牌，也就是遍历集合，给三个玩家发牌
//创建三个玩家
ArrayList<String> xiao = new ArrayList<String>();
ArrayList<String> hei = new ArrayList<String>();
ArrayList<String> bai = new ArrayList<String>();
//底牌
ArrayList<String> dpArray = new ArrayList<String>();
for (int i = 0; i < array.size(); i++) {
String poker = array.get(i);//得到牌
if (i >= array.size() - 3) {
//最后三张牌
dpArray.add(poker);
} else if (i % 3 == 0) {
//对三个玩家取余
xiao.add(poker);
} else if (i % 3 == 1) {
hei.add(poker);
} else if (i % 3 == 2) {
bai.add(poker);
}
}
// 5. 看牌，也就是三个玩家分别遍历自己的牌
lookPoker("小小", xiao);
lookPoker("小黑", hei);
lookPoker("小白", bai);
lookPoker("底牌", dpArray);
}
//看牌的方法
public static void lookPoker(String name, ArrayList<String> array) {
System.out.print(name + "的牌是：");
for (String poker : array) {
System.out.print(poker + " ");
}
System.out.println();//换行
}
}
operation result:
Case: Simulated Battle of the Landlords (upgrade)
Requirements: Realize the shuffling, dealing and viewing of cards in the process of fighting the landlord through the program. Requirement: Sort the cards
Ideas:
- Create a HashMap, the key is the number, and the value is the card
- Create an ArrayList to store the number
- Create an array of suits and an array of points
- Store numbers in HashMap starting from 0, store corresponding cards, and store numbers in ArrayList at the same time
- Shuffle (shuffling is the number), implemented with the shuffle() method of Collections
- Dealing cards (the cards issued are also numbered, in order to ensure that the numbers are sorted, create a TreeSet collection to receive)
- Define the method to look at the cards (traverse the TreeSet collection, obtain the code, and find the corresponding card in the HashMap collection)
- call check method
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.TreeSet;
/*
案例：模拟斗地主（升级）
需求：通过程序实现斗地主过程中的洗牌，发牌和看牌。要求：对牌进行排序
思路：
1. 创建HashMap，键是编号，值是牌
2. 创建ArrayList，存储编号
3. 创建花色数组和点数数组
4. 从0开始往HashMap里面存储编号，并存储对应的牌，同时往ArrayList里面存储编号
5. 洗牌（洗的是编号），用Collections的shuffle（）方法实现
6. 发牌（发的牌也是编号，为了保证编号是排序的，创建TreeSet集合接收）
7. 定义方法看牌（遍历TreeSet集合，获取编码，到HashMap集合找对应的牌）
8. 调用看牌方式
*/
public class PoKerDemo2 {
public static void main(String[] args) {
// 1. 创建HashMap，键是编号，值是牌
HashMap<Integer, String> hm = new HashMap<Integer, String>();
// 2. 创建ArrayList，存储编号
ArrayList<Integer> array = new ArrayList<Integer>();
// 3. 创建花色数组和点数数组
String[] colors = {
"♦", "♣", "♠", "♥" };
String[] numbers = {
"3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A", "2" };
// 4. 从0开始往HashMap里面存储编号，并存储对应的牌，同时往ArrayList里面存储编号
int index = 0;
for (String color : colors) {
for (String num : numbers) {
hm.put(index, color + num);
array.add(index);
index++;
}
}
hm.put(index, "小王");
array.add(index);
index++;
hm.put(index, "大王");
array.add(index);
// 5. 洗牌（洗的是编号），用Collections的shuffle（）方法实现
Collections.shuffle(array);
// 6. 发牌（发的牌也是编号，为了保证编号是排序的，创建TreeSet集合接收）
TreeSet<Integer> bai = new TreeSet<Integer>();
TreeSet<Integer> hei = new TreeSet<Integer>();
TreeSet<Integer> hong = new TreeSet<Integer>();
TreeSet<Integer> dpSet = new TreeSet<Integer>();
for (int i = 0; i < array.size(); i++) {
int x = array.get(i);
if (i >= array.size() - 3) {
dpSet.add(x);
} else if (i % 3 == 0) {
bai.add(x);
} else if (i % 3 == 1) {
hei.add(x);
} else if (i % 3 == 2) {
hong.add(x);
}
}
// 8. 调用看牌方式
look("小白", bai, hm);
look("小黑", hei, hm);
look("小红", hong, hm);
look("底牌", dpSet, hm);
}
// 7. 定义方法看牌（遍历TreeSet集合，获取编码，到HashMap集合找对应的牌）
public static void look(String name, TreeSet<Integer> ts, HashMap<Integer, String> hm) {
System.out.print(name + "的牌是：");
for (Integer key : ts) {
String poker = hm.get(key);
System.out.print(poker + " ");
}
System.out.println();
}
}
operation result:
