第九章編程作業

1. 使用List和Map存放多個圖書資訊,遍歷并輸出.其中商品屬性：編號,名稱,單價,出版社;使用商品編號作為Map中的key.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TestStoreBookInfo {
	
	public static void main(String[] args) {
		
		List<Object> bookList1 = new ArrayList<>();
		bookList1.add("朝花夕拾");
		bookList1.add(10001);
		bookList1.add(21.30);
		bookList1.add("天津人民出版社");
		
		List<Object> bookList2 = new ArrayList<>();
		bookList2.add("人生如逆旅");
		bookList2.add(10002);
		bookList2.add(30.90);
		bookList2.add("四川人民出版社");
		
		List<Object> bookList3 = new ArrayList<>();
		bookList3.add("身份的焦慮");
		bookList3.add(10003);
		bookList3.add(30.80);
		bookList3.add("上海譯文出版社");
		
		List<Object> bookList4 = new ArrayList<>();
		bookList4.add("面紗");
		bookList4.add(10004);
		bookList4.add(9.90);
		bookList4.add("開明出版社");
		
		Map<Integer,List<Object>> bookMap = new HashMap<>();
		
		bookMap.put(1001, bookList1);
		bookMap.put(1002, bookList2);
		bookMap.put(1003, bookList3);
		bookMap.put(1004, bookList4);
		
		for(Integer key:bookMap.keySet()) {
			
			List<Object> booklist = bookMap.get(key);
			
			for(Object bookinfo:booklist) {
				
				System.out.print(bookinfo + " ");
			}
			System.out.println();
		}
		
	}
	
}

2. 使用HashSet和TreeSet存盤多個商品資訊,遍歷并輸出;其中商品屬性：編號,名稱,單價,出版社

要求向其中添加多個相同的商品,驗證集合中元素的唯一性.

提示：向HashSet中添加自定義類的物件資訊,需要重寫hashCode和equals().

向TreeSet中添加自定義類的物件資訊,需要實作Comparable介面,指定比較規則.

import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;

public class WorkTest {
	
	public static void main(String[] args) {
		
		// 自定義通過id來判斷是否是同一個商品
		// 通過自定義hashCode和equals方法實作
		Set<Book> bookSet = new HashSet<>();
		bookSet.add(new Book("朝花夕拾",10001,21.30,"天津人民出版社"));
		bookSet.add(new Book("人生如逆旅",10001,30.90,"四川人民出版社"));
		bookSet.add(new Book("身份的焦慮",10003,30.80,"上海譯文出版社"));
		bookSet.add(new Book("身份的焦慮",10002,30.80,"上海譯文出版社"));
		
		for(Book bb:bookSet) {
			System.out.println(bb);
		}
		
		System.out.println("-----------------");
		
		// 通過價格降序排列
		// 通過Comparable介面
		Set<Book> bookSet2 = new TreeSet<>();
		
		bookSet2.add(new Book("朝花夕拾",10001,21.30,"天津人民出版社"));
		bookSet2.add(new Book("人生如逆旅",10002,30.90,"四川人民出版社"));
		bookSet2.add(new Book("身份的焦慮",10003,9.90,"上海譯文出版社"));
		bookSet2.add(new Book("面紗",10004,9.90,"開明出版社"));
		
		for(Book bb:bookSet2) {
			System.out.println(bb);
		}
	}
}

class Book implements Comparable<Book>{
	
	private String BookName;
	private int Id;
	private double price;
	private String PulishHouse;
	
	public boolean equals(Object obj) {
		// 判斷進行比較的物件是不是Book類的物件
		if (obj instanceof Book) {
			// 如果是,則將此物件強制轉為Book類的物件,并進一步進行判斷
			Book newBook = (Book) obj;
			// 判斷傳入的物件與此物件的ID是否相同,相同則認為是同一本書
			if(this.Id!=newBook.getId()) {
				// 不相同回傳false
				return false;
			}else {
				return true;
			}	
		}else {
			return false;
		}
	}
	
	
	public int hashCode() {
		//hashCode方法回傳的是int型別，并且保證回傳值要與Book物件的屬性有關
		return Id;
	}
	
	public String toString() {
		return "ID:"+ Id + " BookName:" + BookName + " price:" + price + " publishHouse:" + PulishHouse;
	}
	
	@Override
	public int compareTo(Book o) {
		// 先通過價格來比較,逆序
		if(this.price>o.getPrice()) {
			return -1;
		}else if(this.price<o.getPrice()) {
			return 1;
		}else {
			// 價格相等時,用Id比較,逆序
			if(this.Id>o.getId()) {
				return -1;
			}else if(this.Id<o.getId()) {
				return 1;
			}else {
				// 都相同時,回傳0
				return 0;
			}
			
		}
		
	}
	
	public Book() {
		
	}
	
	public Book(String bookName, int id, double price, String pulishHouse) {
		super();
		BookName = bookName;
		Id = id;
		this.price = price;
		PulishHouse = pulishHouse;
	}


	public String getBookName() {
		return BookName;
	}


	public void setBookName(String bookName) {
		BookName = bookName;
	}


	public int getId() {
		return Id;
	}


	public void setId(int id) {
		Id = id;
	}


	public double getPrice() {
		return price;
	}


	public void setPrice(double price) {
		this.price = price;
	}


	public String getPulishHouse() {
		return PulishHouse;
	}


	public void setPulishHouse(String pulishHouse) {
		PulishHouse = pulishHouse;
	}
	
}

3. 實作List和Map資料的轉換.具體要求如下：

功能1：定義方法public static void listToMap(){}將List中Student元素封裝到Map中

     1) 使用構造方法Student(int id,String name,int age,String sex,int age)創建多個學生資訊并加入List;

     2) 遍歷List,輸出每個Student資訊;

     3) 將List中資料放入Map,使用Student的id屬性作為key,使用Student物件資訊作為value;

     4) 遍歷Map,輸出每個Entry的key和value.

功能2：定義方法public static void mapToList(){}將Map中Student映射資訊封裝到List

     1) 創建物體類StudentEntry,可以存盤Map中每個Entry的資訊;

     2) 使用構造方法Student(int id,String name,int age,String sex,int age)創建多個學生資訊,
        并使用Student的id屬性作為key,存入Map;

     3) 創建List物件,每個元素型別是StudentEntry;

     4) 將Map中每個Entry資訊放入List物件.


功能3：說明Comparable介面的作用,并通過分數來對學生進行排序. 

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeSet;

public class OtherTrans {
	
	public static void main(String[] args) {
		
		Students stu1 = new Students(10001,"小王",19,"男",120);
		Students stu2 = new Students(10002,"小劉",20,"女",99);
		Students stu3 = new Students(10003,"小芯",18,"女",103);
		
		List<Students> stuList = new ArrayList<>();
		stuList.add(stu1);
		stuList.add(stu2);
		stuList.add(stu3);
		
		listToMap(stuList);
		
		System.out.println("########################");
		
		// Map轉List
		Map<Integer,Students> stuMap = new HashMap<>();
		stuMap.put(stu1.getId(), stu1);
		stuMap.put(stu2.getId(), stu2);
		stuMap.put(stu3.getId(), stu3);
		
		mapToList(stuMap);
		
		// 按分數排序(Comparable介面實作)
		Set<Students> stuSet = new TreeSet<>();
		stuSet.add(stu1);
		stuSet.add(stu2);
		stuSet.add(stu3);
		
		System.out.println(stuSet);
	}
	
	public static void mapToList(Map<Integer,Students> stuMap){
		// 創建元素型別為Entry的List
		List<Entry<Integer,Students>> stulist = new ArrayList<>();
		// 將Map中每個Entry資訊放入List物件.
		for(Entry<Integer,Students> stuEntry:stuMap.entrySet()) {
			stulist.add(stuEntry);
		}
		
		// 遍歷List并輸出
		for(Entry<Integer,Students> ss:stulist) {
			System.out.println(ss);
		}
		
	}
	
	public static void listToMap(List<Students> stu){
		
		Map<Integer,Students> stuMap = new HashMap<>();
		
		// 遍歷輸出,并添加到map中
		for(Students ss:stu) {
			System.out.println(ss);
			stuMap.put(ss.getId(), ss);
		}
		
		// 輸出key,value
		for(Integer key:stuMap.keySet()) {
			System.out.println(key+"--------"+stuMap.get(key));
		}
	}
}

class Students implements Comparable<Students>{
	
	private int id;
	private String name;
	private int age;
	private String sex;
	private int score;
	
	public int compareTo(Students o) {
		
		if(this.score>o.getScore()) {
			return -1;
		}else if(this.score<o.getScore()) {
			return 1;
		}else {
			if(this.id>o.getId()) {
				return -1;
			}else if(this.id<o.getId()) {
				return 1;
			}else {
				return 0;
			}
		}
	}
	
	
	public String toString() {
		
		return "id:"+id+" 姓名:"+name+" 年齡:"+age+" 性別:"+sex+" 分數:"+score;
	}
	
	
	public Students() {
		
	}
	
	public Students(int id, String name, int age, String sex) {
		
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.sex = sex;
		
	}
	
	public Students(int id, String name, int age, String sex, int score) {
		
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.sex = sex;
		this.score = score;
	}

	
	public int getScore() {
		return score;
	}


	public void setScore(int score) {
		this.score = score;
	}
	
	public int getId() {
		return id;
	}
	
	public void setId(int id) {
		this.id = id;
	}
	
	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 String getSex() {
		return sex;
	}
	
	public void setSex(String sex) {
		this.sex = sex;
	}
}

Comparable介面的作用：

TreeSet底層實際是用TreeMap實作的,內部維持了一個簡化版的TreeMap,通過key來存盤Set的元素. 
TreeSet內部需要對存盤的元素進行排序,因此,我們對應的類需要實作Comparable介面.這樣,
才能根據compareTo()方法比較物件之間的大小,才能進行內部排序.