集合之Map【TreeMap】

package com.Lucky.Map;
 
import java.util.Comparator;
import java.util.TreeMap;
 
/*
        TreeMap:底层结构和TreeSet一样是红黑树
                可以排序/无重复/无索引
 
           注意点：排序方法也是和TreeSet一样【自然排序/比较器排序】
 
 */
public class TreeMapDemo {
    public static void main(String[] args) {
        /**
         * 要求1：键储存id，值储存商品   按照id升序排列【默认的】和降序排列【利用比较器排序】
         */
        TreeMap<Integer,String> Tmap=new TreeMap<>(new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2-o1;
            }
        });
 
        Tmap.put(1,"联想拯救者");
        Tmap.put(5,"外星人");
        Tmap.put(9,"惠普");
        Tmap.put(4,"华为");
 
        System.out.println(Tmap);
 
 
 
 
        /**
         * 要求2：键储存学生对象，值储存种族   按照年龄排序/如果年龄一样就比较姓名字母排序
         */
          TreeMap<Student,String> Smap=new TreeMap<>();
 
           Student str1=new Student("唯易",22);
           Student str2=new Student("珠峰",20);
           Student str3=new Student("信仰",22);
           Student str4=new Student("张老三",26);
 
            Smap.put(str1,"汉");
            Smap.put(str2,"少数名族");
            Smap.put(str3,"少数名族");
            Smap.put(str4,"汉");
 
 
        System.out.println(Smap);
    }
}

材料：

 1 package com.Lucky.Map;
 2 
 3 import java.util.Objects;
 4 
 5 public class Student implements Comparable<Student>{
 6     private String name;
 7     private int age;
 8 
 9     public Student() {
10     }
11 
12     public Student(String name, int age) {
13         this.name = name;
14         this.age = age;
15     }
16 
17     public String getName() {
18         return name;
19     }
20 
21     public void setName(String name) {
22         this.name = name;
23     }
24 
25     public int getAge() {
26         return age;
27     }
28 
29     public void setAge(int age) {
30         this.age = age;
31     }
32 
33     @Override
34     public boolean equals(Object o) {
35         if (this == o) return true;
36         if (o == null || getClass() != o.getClass()) return false;
37         Student student = (Student) o;
38         return age == student.age && Objects.equals(name, student.name);
39     }
40 
41     @Override
42     public int hashCode() {
43         return Objects.hash(name, age);
44     }
45 
46     @Override
47     public String toString() {
48         return "Student{" +
49                 "name='" + name + '\'' +
50                 ", age=" + age +
51                 '}';
52     }
53 
54     @Override
55     public int compareTo(Student o) {
56         //比较年龄
57        int res=this.getAge()-o.getAge();
58        if(res==0){
59            //年龄相等，就比较姓名
60            res =  this.getName().compareTo(o.getName());
61        }
62        return  res;
63     }
64 }

View Code

综合小练习：

package com.Lucky.Map;
/*
     统计字符串str="ACBBSABCBASSAABCCSAAACBCSAA";
     统计每一个字符出现的次数，按照从多到少排列
 
 */
 
import java.util.StringJoiner;
import java.util.TreeMap;
import java.util.function.BiConsumer;
 
/**
 *    统计个数：1.计数器思想  2.Map思想
 *     应用场景：HashMap用于不用排序的结果
 *             TreeMap用于要进行排序的结果
 */
public class TreeMapDemo1 {
    public static void main(String[] args) {
        String str="ACBBSABCBASSAABCCSAAACBCSAA";
        //创建TreeMap对象
        TreeMap<Character,Integer> tmap=new TreeMap<>();
 
 
 
        for (int i = 0; i < str.length(); i++) {
            char c=str.charAt(i);
             if(tmap.containsKey(c)){
                 //获取次数
                 int sum=tmap.get(c);
                 sum++;
                 tmap.put(c,sum);
             }else {
                 tmap.put(c,1);
             }
        }
 
 
       //遍历数据,格式  A(10)B(6)C(6)S(5)
        //方法1  StringBuilder
        StringBuilder builder=new StringBuilder();
        tmap.forEach(new BiConsumer<Character, Integer>() {
            @Override
            public void accept(Character character, Integer integer) {
                builder.append(character).append("(").append(integer).append(")");
            }
        });
        System.out.println(builder);
 
        //方法2  StringJoiner
        System.out.println("---------StringJoiner----------");
        StringJoiner joiner=new StringJoiner("","","");
        tmap.forEach((key,val)->{
            joiner.add(key+"").add("(").add(val+"").add(")");
        });
        System.out.println(joiner);
 
    }
}