1.TreeMap类

• 概述：键是红黑树结构，可以保证键的排序和唯一性

遍历集合；

package com.bigdat.java.day22;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
/*TreeMap类概述键是红黑树结构，可以保证键的排序和唯一性*/
public class TreeMapDemo1 {public static void main(String[] args) {//创建集合对象TreeMap<Integer, String> treeMap = new TreeMap();//向集合中添加元素treeMap.put(1001, "张三");treeMap.put(1002, "李四");treeMap.put(1003, "王五");treeMap.put(1001, "二狗子"); //结果会对张三的结果产生压盖，就只会产生二狗子treeMap.put(1004, "王二麻子");//遍历集合Set<Integer> integers = treeMap.keySet();for (Integer integer : integers) {String s = treeMap.get(integer);System.out.println("编号："+integer+",姓名："+s);}System.out.println("===============================================");Set<Map.Entry<Integer, String>> entries = treeMap.entrySet();Iterator<Map.Entry<Integer, String>> iterator = entries.iterator();while (iterator.hasNext()){Map.Entry<Integer, String> next = iterator.next();Integer key = next.getKey();String value = next.getValue();System.out.println("编号："+key+",姓名："+value);}}
}

HashMap<Student, String>

注意事项；排序分为自然排序

• 自然排序：引用类型必须实现Comparable接口(因为源码中compar有一个向下转型的步骤)，然后重写compareTo()方法；
  根据需求先比较什么什么就是主要条件因为红黑树采用中序遍历^,如下

@Overridepublic int compareTo(Student4 o) {int i = this.name.compareTo(o.name);//姓名一样，年龄不一定一样int i2 = (i == 0) ? this.age - o.age : i;return i2;}

• 比较器排序：调用的是引用类型中的有参构造器
  //TreeMap<Student4, Integer> tMap = new TreeMap<>();
  ，引用类中必须实现Comparator接口。然后重写compare()方法或直接在main()方法中实现匿名内部类操作

public class TreeMapDemo2 {public static void main(String[] args) {//创建集合对象//TreeMap<Student4, Integer> tMap = new TreeMap<>();//比较器排序//TreeMap tMap = new <Student4, Integer>TreeMap(new Student4());//匿名内部类实现比较器排序TreeMap<Student4, Integer> tMap = new TreeMap(new Comparator<Student4>(){@Overridepublic int compare(Student4 o1, Student4 o2) {return 0;}});

代码如下：

import java.util.*;/*HashMap<Student,String>*/
public class TreeMapDemo2 {public static void main(String[] args) {//创建集合对象//TreeMap<Student4, Integer> tMap = new TreeMap<>();//比较器排序//TreeMap tMap = new <Student4, Integer>TreeMap(new Student4());//匿名内部类实现比较器排序TreeMap<Student4, Integer> tMap = new TreeMap(new Comparator<Student4>(){@Overridepublic int compare(Student4 o1, Student4 o2) {return 0;}});//创建学生类对象Student4 s1 = new Student4("白骨精",10);Student4 s2 = new Student4("观世音菩萨",32);Student4 s3 = new Student4("铁扇公主",27);Student4 s4 = new Student4("白骨精",10);Student4 s5 = new Student4("太上老君",55);Student4 s6 = new Student4("比较的太上老君",55);//向集合中添加元素tMap.put(s1,1001);tMap.put(s2,1002);tMap.put(s3,1003);tMap.put(s4,1004);tMap.put(s5,1005);tMap.put(s6,1006);//遍历集合Set<Map.Entry<Student4, Integer>> entries = tMap.entrySet();Iterator<Map.Entry<Student4, Integer>> iterator = entries.iterator();while (iterator.hasNext()){Map.Entry<Student4, Integer> next = iterator.next();Student4 key = next.getKey();Integer value = next.getValue();System.out.println("学生:"+key+",编号："+value);}}
}

引用类型(Stuedent)代码如下：

package com.bigdat.java.day22;
import java.util.Comparator;/*创建学生对象*/
public class Student4 implements Comparator<Student4> {private String name;private int age;public Student4() {}public Student4(String name, int age) {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;}@Overridepublic String toString() {return "Student4{" +"name='" + name + '\'' +", age=" + age +'}';}/*如果走自然排序方法的话：引用类型实现Comparable() 方法然后重写compareTo 方法@Overridepublic int compareTo(Student4 o) {int i = this.name.compareTo(o.name);//姓名一样，年龄不一定一样int i2 = (i == 0) ? this.age - o.age : i;return i2;}*///比较器排序，创建集合时需要传参，然后引用类型必须实现 Comparator 方法//然后再重写 compare 方法@Overridepublic int compare(Student4 o1, Student4 o2) {int i = o1.age - o2.getAge();return i;}}

TreeMap 遍历方法如下：

package com.bigdat.java.day22;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
/*TreeMap类概述键是红黑树结构，可以保证键的排序和唯一性*/
public class TreeMapDemo1 {public static void main(String[] args) {//创建集合对象TreeMap<Integer, String> treeMap = new TreeMap();//向集合中添加元素treeMap.put(1001, "张三");treeMap.put(1002, "李四");treeMap.put(1003, "王五");treeMap.put(1001, "二狗子"); //结果会对张三的结果产生压盖，就只会产生二狗子treeMap.put(1004, "王二麻子");//遍历集合Set<Integer> integers = treeMap.keySet();for (Integer integer : integers) {String s = treeMap.get(integer);System.out.println("编号："+integer+",姓名："+s);}System.out.println("===============================================");Set<Map.Entry<Integer, String>> entries = treeMap.entrySet();Iterator<Map.Entry<Integer, String>> iterator = entries.iterator();while (iterator.hasNext()){Map.Entry<Integer, String> next = iterator.next();Integer key = next.getKey();String value = next.getValue();System.out.println("编号："+key+",姓名："+value);}}
}