Map&Collections&Poker

文章目录

Map
Collections

Map

描述：

键映射到值的对象, 地图不能包含重复的键; 每个键可以映射到最多一个值。
这个接口取代了Dictionary类，它是一个完全抽象的类而不是接口。

Map&Collection区别
- Map 存储的是键值对形式的元素，键唯一，值可以重复。
- Collection 存储的是单独出现的元素，子接口Set元素唯一，子接口List元素可重复。

Map接口功能

添加功能

V put(K key,V value):添加元素。
	若存在则返回更新之前的value值，不存在返回NULL，且属于可选择返回：可以返回，也可以不返回。

/*for example*/
Map<String, String> map = new HashMap<String, String>();
System.out.println(map.put("Tom", "2"));	//NULL
System.out.println(map.put("Tom", "3"));	//2

删除功能

void clear():移除所有的键值对元素.
V remove(Object key)：根据键删除键值对元素,并把值返回.
System.out.println("remove:" + map.remove("Tom));	//3

判断功能

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.

获取功能

Set<Map.Entry<K,V>> entrySet():返回键值对.
	/*for example*/
	Set<Map.Entry<String, String>> set = map.entrySet();

V get(Object key):根据键获取值.
	/*for example*/
	System.out.println("get:" + map.get("Tom"));	//显示3.

Set<K> keySet():获取集合中所有键的集合.
	/*for example*/
	Set<String> set = map.keySet();

Collection<V> values():获取集合中所有值的集合.
	/*for example*/
	Collection<String> con = map.values();

/*conclusion*/
Map<String, String> map = new HashMap<String, String>();
Set<Map.Entry<String, String>> set = map.entrySet();		
		for (Map.Entry<String, String> Aa : set) {			
			String key = Aa.getKey();
			String value = Aa.getValue();
			System.out.println(key + "---" + value);
		}

长度功能

int size()：返回集合中的键值对的对数.
		/*for example*/
		System.out.println("size:"+map.size());

Map集合的遍历

键->值.

/*for example*/
Map<String, String> map = new HashMap<String, String>();
		Set<String> set = map.keySet();
		
		for (String key : set) {			
			String value = map.get(key);
			System.out.println(key + "---" + value);
		}

键值对->找键和值

Map<String, String> map = new HashMap<String, String>();		
Set<Map.Entry<String, String>> set = map.entrySet();

		/*遍历键值对*/
		for (Map.Entry<String, String> me : set) {			
			String key = me.getKey();
			String value = me.getValue();
			System.out.println(key + "---" + value);
		}

HashMap集合

HashMap<String,String>

		HashMap<String, String> hm = new HashMap<String, String>();
		
		-键值对添加区域-	//hm.put("key","value")

		/*遍历*/
		Set<String> set = hm.keySet();
		for (String key : set) {
			String value = hm.get(key);
			System.out.println(key + "---" + value);
		}

HashMap<Integer,String>

HashMap<Integer, String> hm = new HashMap<Integer, String>();

	-键值对添加区域-	//hm.put(key,"value")

	// 遍历
	Set<Integer> set = hm.keySet();
	for (Integer key : set) {
		String value = hm.get(key);
		System.out.println(key + "---" + value);
	}

HashMap<String,Student>

HashMap<String, Student> hm = new HashMap<String, Student>();

	-键值对添加区域-	
		//hm.put("key",value) value=objecet对象，如student.

	// 遍历
	Set<String> set = hm.keySet();
	for (String key : set) {			
		Student value = hm.get(key);
		System.out.println(key + "---" + value.getName() + "---"
				+ value.getAge());
}

HashMap<Student,String>

HashMap<Student, String> hm = new HashMap<Student, String>();

		-键值对添加区域-	
				//hm.put(value,"key") value=objecet对象，如student.	

		// 遍历
		Set<Student> set = hm.keySet();
		for (Student key : set) {
			String value = hm.get(key);
			System.out.println(key.getName() + "---" + key.getAge() + "---"
					+ value);
	}

TreeMap集合

TreeMap<String,String>

TreeMap<String, String> tm = new TreeMap<String, String>();
		
		-键值对添加区域-	
						//hm.put("key","value") 

		// 遍历集合
		Set<String> set = tm.keySet();
		for (String key : set) {
			String value = tm.get(key);
			System.out.println(key + "---" + value);
		}

TreeMap<Student,String>

/*for example*/

/*自动生成学生类*/
public class Student {
	private String name;
	private int age;

	public Student() {
		super();
	}

	public Student(String name, int age) {
		super();
		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 void setAge(int age) {
		this.age = age;
	}
}

/*测试主类*/
import java.util.Comparator;
import java.util.Set;
import java.util.TreeMap;

/*TreeMap<Student,String>*/

public class TreeMapMain {
	public static void main(String[] args) {

		//匿名抽象借口重写
		TreeMap<Student, String> tm = new TreeMap<Student, String>(
				new Comparator<Student>() {					
					@Override
					public int compare(Student s1, Student s2) {
						//第一个变量-第二个=升序排列.
						// 优先级年龄
						int num = s1.getAge() - s2.getAge();
						// 优先级名字
						int num2 = num == 0 ? s1.getName().compareTo(
								s2.getName()) : num;
						return num2;
					}
				});
		
		Student s1 = new Student("Aa", 30);
		Student s2 = new Student("Bb", 35);
		Student s3 = new Student("Cc", 33);
		Student s4 = new Student("Dd", 32);
		Student s5 = new Student("Ee", 33);
		
		tm.put(s1, "01");
		tm.put(s2, "02");
		tm.put(s3, "03");
		tm.put(s4, "04");
		tm.put(s5, "05");

		// 遍历
		Set<Student> set = tm.keySet();
		for (Student key : set) {
			String value = tm.get(key);
			System.out.println(key.getName() + "---" + key.getAge() + "---"
					+ value);
		}
	}
}

多层嵌套

hashMap&hashMap

/*for example*/
//注意导包:Ctrl+Shift+O

package TestAa;

import java.util.HashMap;
import java.util.Set;

public class HashMapHashMap {
	public static void main(String[] args) {

		HashMap<String, HashMap<String, Integer>> bigMap = new HashMap<String, HashMap<String, Integer>>();

		// 子图一
		HashMap<String, Integer> oneMap = new HashMap<String, Integer>();
		oneMap.put("Tom", 5);
		oneMap.put("Jack", 2);
		bigMap.put("one", oneMap);

		// 子图二
		HashMap<String, Integer> twoMap = new HashMap<String, Integer>();
		twoMap.put("John", 3);
		twoMap.put("Suqi", 4);
		bigMap.put("two", twoMap);

		// 遍历集合
		Set<String> bigMapSet = bigMap.keySet();
		for (String bigMapKey : bigMapSet) {
			System.out.println(bigMapKey);

			HashMap<String, Integer> bigMapValue = bigMap.get(bigMapKey);
			Set<String> sonMapSet = bigMapValue.keySet();
			for (String sonValue : sonMapSet) {
				Integer value = bigMapValue.get(sonValue);
				System.out.println("\t" + sonValue + "---" + value);
			}
		}
	}
}

统计字符串字母频数

public class TreeMap{
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入一个字符串：");
		String line = sc.nextLine();
		
		TreeMap<Character, Integer> tm = new TreeMap<Character, Integer>();		
		char[] chs = line.toCharArray();
		
		for(char ch : chs){			
			Integer i =  tm.get(ch);			
			if(i == null){
				tm.put(ch, 1);
			}else {				
				i++;
				tm.put(ch,i);
			}
		}
				
		StringBuilder sb=  new StringBuilder();	
		
		Set<Character> set = tm.keySet();
		for(Character key : set){
			Integer value = tm.get(key);
			sb.append(key).append("(").append(value).append(")");
		}		
		String result = sb.toString();
		System.out.println("result:"+result);
	}
}

忽略以下.
- HashMap嵌套ArrayList
- ArrayList嵌套HashMap
- 多层嵌套

Collections

描述：注意与collection的区别,是针对集合进行操作的工具类.

Collection&Collections差异
- Collection 是单列集合的顶层接口，有两个子接口List和Set.
- Collections 是针对集合进行操作的工具类，可以对集合进行排序和查找等.

常用函数

public static void sort(List list)

List<Integer> list = new ArrayList<>();
list.add(value);			//value为Integer数据类型.
Collections.sort(list);

public static int binarySearch(List<?> list,T key)

/*二分查找法，返回Index，未找到为-[(List.size)+1]*/
System.out.println("binarySearch:" + Collections.binarySearch(list, 60));

public static T max(Collection<?> coll)

/*for example，获取最大值.*/
System.out.println("max:" + Collections.max(list));

public static void reverse(List<?> list)

Collections.reverse(list);	//List反转
System.out.println("list:" + list);

public static void shuffle(List<?> list)

Collections.shuffle(list);	//List随机打乱.
System.out.println("list:" + list);

代码实例：

ArrayList对象排序

public class CollectionsDemo {
	public static void main(String[] args) {
		
		List<Student> list = new ArrayList<Student>();
		- 添加对象数据区域-
		- 		
		// Collections.sort(list);
		// 比较器排序，如果同时有自然排序和比较器排序，以比较器排序为主
		Collections.sort(list, new Comparator<Student>() {
			@Override
			public int compare(Student s1, Student s2) {
				int num = s2.getAge() - s1.getAge();
				int num2 = num == 0 ? s1.getName().compareTo(s2.getName())
						: num;
				return num2;
			}
		});
		
		for (Student s : list) {
			System.out.println(s.getName() + "---" + s.getAge());
		}
	}
}

斗地主洗牌&发牌&排序-(来源于网上.)

package cn.itcast_04;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.TreeSet;

/*
 * 思路：
 * 		A:创建一个HashMap集合
 * 		B:创建一个ArrayList集合
 * 		C:创建花色数组和点数数组
 * 		D:从0开始往HashMap里面存储编号，并存储对应的牌
 *        同时往ArrayList里面存储编号即可。
 *      E:洗牌(洗的是编号)
 *      F:发牌(发的也是编号，为了保证编号是排序的，就创建TreeSet集合接收)
 *      G:看牌(遍历TreeSet集合，获取编号，到HashMap集合找对应的牌)
 */
public class PokerDemo {
	public static void main(String[] args) {
		// 创建一个HashMap集合
		HashMap<Integer, String> hm = new HashMap<Integer, String>();

		// 创建一个ArrayList集合
		ArrayList<Integer> array = new ArrayList<Integer>();

		// 创建花色数组和点数数组
		// 定义一个花色数组
		String[] colors = { "♠", "♥", "♣", "♦" };
		// 定义一个点数数组
		String[] numbers = { "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q",
				"K", "A", "2", };

		// 从0开始往HashMap里面存储编号，并存储对应的牌,同时往ArrayList里面存储编号即可。
		int index = 0;

		for (String number : numbers) {
			for (String color : colors) {
				String poker = color.concat(number);
				hm.put(index, poker);
				array.add(index);
				index++;
			}
		}
		hm.put(index, "小王");
		array.add(index);
		index++;
		hm.put(index, "大王");
		array.add(index);

		// 洗牌(洗的是编号)
		Collections.shuffle(array);

		// 发牌(发的也是编号，为了保证编号是排序的，就创建TreeSet集合接收)
		TreeSet<Integer> fengQingYang = new TreeSet<Integer>();
		TreeSet<Integer> linQingXia = new TreeSet<Integer>();
		TreeSet<Integer> liuYi = new TreeSet<Integer>();
		TreeSet<Integer> diPai = new TreeSet<Integer>();

		for (int x = 0; x < array.size(); x++) {
			if (x >= array.size() - 3) {
				diPai.add(array.get(x));
			} else if (x % 3 == 0) {
				fengQingYang.add(array.get(x));
			} else if (x % 3 == 1) {
				linQingXia.add(array.get(x));
			} else if (x % 3 == 2) {
				liuYi.add(array.get(x));
			}
		}

		// 看牌(遍历TreeSet集合，获取编号，到HashMap集合找对应的牌)
		lookPoker("风清扬", fengQingYang, hm);
		lookPoker("林青霞", linQingXia, hm);
		lookPoker("刘意", liuYi, hm);
		lookPoker("底牌", diPai, hm);
	}

	// 写看牌的功能
	public static void lookPoker(String name, TreeSet<Integer> ts,
			HashMap<Integer, String> hm) {
		System.out.print(name + "的牌是：");
		for (Integer key : ts) {
			String value = hm.get(key);
			System.out.print(value + " ");
		}
		System.out.println();
	}
}

文章目录

Map

Collections

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