集合Collection ----Set集合
set系列集合：添加的元素是 无序，不重复，无索引的
----HashSet： 无序，不重复，无索引
------LinkHashSet<>:有序不重复无索引（添加顺序）
----TreeSet： 排序（按照大小默认升序排序，是可排序集合），不重复，无索引
HashSet：不重复，无序
set集合去重复的流程: 1.对象调用hashcode() 方法获取哈希值进行比较 false---不重复
2.如果为true，则进行equals比较
总结：如果set对象认为两个集合的内容一样就重复，重写hashcode()和equals方法
set集合无序的原因是：底层采用了哈希表存储元素
import java.util.HashSet; import java.util.Objects; import java.util.Set; class Sheep{ private String name; private int age; Sheep(){ } public Sheep(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; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Sheep sheep = (Sheep) o; return age == sheep.age && Objects.equals(name, sheep.name); } @Override public int hashCode() { return Objects.hash(name, age); } @Override public String toString() { return "Sheep{" + "name='" + name + '\'' + ", age=" + age + '}'; } } public class HashSetDemo1 { public static void main(String[] args) { Set<Sheep> sets=new HashSet<>(); Sheep s1 = new Sheep("懒洋洋",6); Sheep s2 = new Sheep("暖羊羊",8); Sheep s3 = new Sheep("懒洋洋",6); sets.add(s1); sets.add(s2); sets.add(s3); System.out.println(sets); // [Sheep{name='暖羊羊', age=8}, Sheep{name='懒洋洋', age=6}]
// 如果没有重写hashcode()和equals，则输出：[Sheep{name='暖羊羊', age=8}, Sheep{name='懒洋洋', age=6}, Sheep{name='懒洋洋', age=6}]
} }
LinkHashSet：每个元素都添加一个链来维护添加顺序
import java.util.LinkedHashSet; import java.util.Set;
public class LinkHashSetDemo1 { public static void main(String[] args) { Set<String> sets = new LinkedHashSet<>(); sets.add("沸羊羊"); sets.add("喜羊羊"); sets.add("暖羊羊"); sets.add("喜羊羊"); System.out.println(sets); // [沸羊羊, 喜羊羊, 暖羊羊] } }
TreeSet:
1.有值特性的元素进行升序排序
2.String排序按照首字母的 ASCII码值排序
3.引用数据类型（默认无法排序，所以需要定制排序的大小规则）
a.直接为对象的类实现比较器规则接口Comparable，重写比较方法
b.直接为集合设置比较器Comparator对象，重写比较方法
总结：如果类和集合都带有比较规则，优先使用集合自带的比较规则
package com.day05; import java.util.Comparator; import java.util.Set; import java.util.TreeSet; class Wolf implements Comparable<Wolf>{ private String name; private int age; //重写比较方法 w1.compareTo(w) // 比较者：this 被比较者：w @Override public int compareTo(Wolf w){ //比价规则！！ //比较者大于被比较者，返回正数(1) //比较者小于被比较者，返回负数(-1) //比较者等于被比较者，返回0 // if(this.age>w.age){ // return 1; // }else if(this.age<w.age){ // return -1; // } // return 0; return this.age-w.age; } Wolf(){ } public Wolf(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; } @Override public String toString() { return "Wolf{" + "name='" + name + '\'' + ", age=" + age + '}'; } } public class TreeSetDemo1 { public static void main(String[] args) {
//---------------第一种-------------------// 自然排序 Set<Wolf> sets=new TreeSet<>(); sets.add(new Wolf("红太狼",24)); sets.add(new Wolf("灰太狼",28)); sets.add(new Wolf("小灰灰",12)); System.out.println(sets); //--------------第二种--------------------// Set<Wolf> setss=new TreeSet<>(new Comparator<Wolf>() { // 匿名对象 比较器排序 @Override public int compare(Wolf o1, Wolf o2) { return o2.getAge()-o1.getAge(); } }); setss.add(new Wolf("红太狼",24)); setss.add(new Wolf("灰太狼",28)); setss.add(new Wolf("小灰灰",12)); System.out.println(setss); } }
package com.shujia.day18; import java.util.Comparator; import java.util.TreeSet; public class TreeSetDemo1 { public static void main(String[] args) { //创建集合对象 TreeSet<Student> students = new TreeSet<Student>(new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { //o1-o2为从小到大排序 int i=o1.getName().length()-o2.getName().length(); int i1 = i == 0 ? o1.getName().compareTo(o2.getName()):i; int i2 = i1 == 0 ? o1.getAge() - o2.getAge():i1; return i2; } }); //创建学生对象 Student s1 = new Student("zhongqihang", 23); Student s2 = new Student("guoao", 24); Student s3 = new Student("sunduoqin", 28); Student s4 = new Student("kuangjie", 27); Student s5 = new Student("chenchuan", 26); Student s6 = new Student("wangyouhu", 29); Student s7 = new Student("chenzhiqiang", 29); Student s8 = new Student("chenchuan", 27); //添加元素 students.add(s1); students.add(s2); students.add(s3); students.add(s4); students.add(s5); students.add(s6); students.add(s7); students.add(s8); //遍历 for (Student s : students) { System.out.println(s.getName()+"----"+s.getAge()); } //guoao----24 //kuangjie----27 //chenchuan----26 //chenchuan----27 //sunduoqin----28 //wangyouhu----29 //zhongqihang----23 //chenzhiqiang----29 } } class Student { private String name; private int age; public Student() { } public Student(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; } }
