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 Tmap=new TreeMap<>(new Comparator() {
@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 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{
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

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 tmap=new TreeMap<>();
for (int i = 0; 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() {
@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);
}
}