14、集合--TreeSet的使用和相关说明

布满荆棘的人生 2021-12-17 06:55 124阅读 0赞

TreeSet是SortedSet接口的唯一实现

可以确保集合元素**处于排序状态**

TreeSet并不是根据元素的插入顺序进行排序的

而是根据元素实际的值进行排序

与HashSet集合采用hash算法来决定元素的存储位置

TreeSet采用**红黑树**的数据结构进行排序处理

Treeset支持两种排序方法

1、自然排序

2、定制排序

需要实现CompareTo 接口方法  
public int compareTo()  
TressSet会调用每个元素的该方法比较，进而确定在集合中的位置  
返回0 代表相等，返回负数当前元素小，整数当前元素属大  
会增加系统的负担

测试：

public class Person implements Comparable {
        private String name;
        private int 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 "Person{
         " +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }
    
        public  Person(){
    
        }
    
        public boolean equals(Object obj) {
            if (this == obj)
                return  true;
            if (obj == null)
                return  false;
            if (getClass() != obj.getClass())
                return false;
    
            Person other = (Person) obj;
            if (age != other.age)
                return false;
            if (name == null){
                if (other.name != null){
                    return false;
                }
            }else  if (!name.equals(other.name)){
                return false;
            }
    
            return true;
        }
    
        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + age;
            result = prime * result + ((name == null) ? 0:name.hashCode());
            return result;
        }
    
        @Override
        public int compareTo(Object o) {
    
            //按名字排序
            if (o instanceof Person){
                Person person = (Person) o;
                return this.name.compareTo(person.name);
            }else {
                throw  new ClassCastException("不能进行强制类型转换");
            }
        }
    }

public static void main(String[] args) {
    
            TreeSet set = new TreeSet();
    
            set.add(new Person("aa",4));
            set.add(new Person("cc",14));
            set.add(new Person("ee",2));
            set.add(new Person("bb",22));
            set.add(new Person("dd",12));
    
            Iterator it = set.iterator();
            while(it.hasNext()){
                Object o = it.next();
                System.out.println(o);
            }
        }

![1488757-20190511231851492-709071658.png][]

如果要按照年龄进行排序：

此时直接修改Person中的方法：

@Override
        public int compareTo(Object o) {
            //按照年龄排序
            if (o instanceof  Person){
                Person p = (Person) o;
                return this.age - p.age;
            }else {
                throw  new ClassCastException("不能进行强制类型转换");
            }
        }

此时的运行结果：

![1488757-20190511232028142-196731545.png][]

直接写compareTo方法

此时的Person不需要实现**Comparable接口**

public static void main(String[] args) {
        
    
        Comparator comparator = new Comparator() {
        
            @Override
            public int compare(Object o1, Object o2) {
        
    
                if (o1 instanceof  Person && o2 instanceof  Person){
        
                    Person p1= (Person) o1;
                    Person p2 = (Person) o2;
    
                    return p1.getAge() - p2.getAge();
                }else {
        
                    throw  new ClassCastException("不能进行强制类型转换");
                }
            }
        };
    
        TreeSet set = new TreeSet(comparator);
    
        set.add(new Person("aa",4));
        set.add(new Person("cc",14));
        set.add(new Person("ee",2));
        set.add(new Person("bb",22));
        set.add(new Person("dd",12));
    
        Iterator it = set.iterator();
        while(it.hasNext()){
        
            Object o = it.next();
            System.out.println(o);
        }
    }

![1488757-20190511232602520-1366981598.png][]

转载于:https://www.cnblogs.com/Mrchengs/p/10850580.html

[1488757-20190511231851492-709071658.png]: /images/20211217/e195ab4e00b14837a5f4f52a8fd7865d.png
[1488757-20190511232028142-196731545.png]: /images/20211217/b2ca03ae27674b5085a21941c0aff32f.png
[1488757-20190511232602520-1366981598.png]: /images/20211217/c1c837c9167c4c01a5a1ec7b60483698.png