Set子接口

Set子接口

特点：无序、无下标、元素不可重复

方法：全部继承自Collection中的方法

Set实现类

HashSet [重点]：

基于HashCode实现元素不重复

当存入元素的哈希码相同时，会调用equals进行确认， 如结果为true, 则拒绝后者存入

eg : 

public class Person implements Comparable<Person>{
    private String name;
    private int age;
    public Person() {
    }
    public Person(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 "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    /*@Override
    public int hashCode() {
        int n1 = this.name.hashCode();
        int n2 = this.age;
        return n1+n2;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null){
            return false;
        }
        if (obj instanceof Person){
            Person p = (Person)obj;
            if (this.name.equals (p.getName ())&&this.age== p.getAge()){
                return true;
            }
        }
        return false;
    }*/
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass ( ) != o.getClass ( )) return false;
        Person person = (Person) o;
        return age == person.age && Objects.equals (name, person.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash (name, age);
    }
    //先按姓名比，然后再按年龄比
    @Override
    public int compareTo(Person o) {
        int n1 = this.getName().compareTo(o.getName());
        int n2 = this.age-o.getAge();
        return n1==0?n2:n1;
    }
}

/**
 * HashSet集合的使用
 * 存储结构：哈希表（数组+链表+红黑树（JDK1.8））
 * 存储过程（重复依据）
 * 1.根据hashcode计算保存的位置，如果此位置为空，则直接保存，如果不为空执行第二部
 * 2.在执行equals方法，如果equals方法为true，则认为是重复，否则，形成链表
 * @author
 */
public class Demo03 {
    public static void main(String[] args) {
        //创建集合
        HashSet<Person> persons = new HashSet<>();
        //1.添加数据
        Person p1 = new Person("张三",18);
        Person p2 = new Person("李四",16);
        Person p3 = new Person("王二",19);
        persons.add (p1);
        persons.add (p2);
        persons.add (p3);
        //persons.add (p1);
        persons.add (new Person("李四",16));
        System.out.println("元素个数"+persons.size());
        System.out.println(persons.toString());
        //2.删除操作
        //persons.remove (p1);
        //persons.remove (new Person("李四",16));
        //System.out.println(persons.toString());
        //3.遍历 重点
        //3.1使用增强for
        for (Person person : persons){
            System.out.println (person.toString());
        }
        //3.2迭代器
        Iterator<Person> it = persons.iterator();
        while (it.hasNext ( )){
            System.out.println (it.next());
        }
        //4.判断
        System.out.println(persons.contains(new Person("李四",16)));
        System.out.println (persons.isEmpty());//判断是否为空
    }
}

TreeSet：

基于排列顺序实现元素不重复

实现了SortedSet接口，对集合元素自动排序

元素对象的类型必须实现Comparable接口，指定排序规则

通过CompareTo方 法确定是否为重复元素

eg : 

/**
 * TreeSet保存数据
 * 存储结构：红黑树
 * 要求：元素必须要实现Comparable接口,compareTO()方法返回值为0.认为是重复元素
 * @author
 */
public class Demo05 {
    public static void main(String[] args) {
        //创建集合
        TreeSet<Person> persons = new TreeSet<>();
        //1.添加元素
        Person p1 = new Person("xyz",18);
        Person p2 = new Person("abc",16);
        Person p3 = new Person("sad",19);
        Person p4 = new Person("sad",29);
        persons.add (p1);
        persons.add (p2);
        persons.add (p3);
        persons.add (p4);
        System.out.println ("元素个数："+persons.size());
        System.out.println (persons.toString());
        //2.删除
        //persons.remove (p1);
        //System.out.println (persons.toString ());
        //3.遍历
        //3.1增强for
        for (Person person : persons) {
            System.out.println (person.toString ());
        }
        //3.2使用迭代器
        Iterator<Person> it = persons.iterator ( );
        while (it.hasNext ( )){
            System.out.println (it.next () );
        }
        //4.判断
        System.out.println (persons.contains(new Person("xyz",18)));
        System.out.println(persons.isEmpty());//判断是否为空
    }
}

/**
 * TreeSet的使用
 * Comparator:实现定制比较（比较器）
 * Comparable:可比较的
 * @author
 */
public class Demo06 {
    public static void main(String[] args) {
        //创建集合,并指定比较规则
        TreeSet<Person> persons =new TreeSet<>(new Comparator<Person> ( ) {
            @Override
            public int compare(Person o1, Person o2) {
                int n1 = o1.getAge()-o2.getAge();
                int n2 = o1.getName().compareTo(o2.getName());
                return n1==0?n2:n1;
            }
        });
        Person p1 = new Person("xyz",18);
        Person p2 = new Person("abc",16);
        Person p3 = new Person("sad",19);
        Person p4 = new Person("sda",19);
        persons.add (p1);
        persons.add (p2);
        persons.add (p3);
        persons.add (p4);
        System.out.println (persons.toString());
    }
}