treeset

• 储存结构：红黑树
• 要求：元素必要实现comparable接口，compareTo()方法返回值为0，则认为重复
  

public class Demo01 {
    public static void main(String[] args) {
        //创建集合
        TreeSet treeSet = new TreeSet<>();
        //1.添加元素
        Person s1 = new Person("刘", 20);
        Person s2 = new Person("关", 30);
        Person s3 = new Person("张", 40);
        Person s4 = new Person("张", 20);

        treeSet.add(s1);
        treeSet.add(s2);
        treeSet.add(s3);
        treeSet.add(s4);

        System.out.println(treeSet);
        System.out.println(treeSet.size());
    }
}

package Collection.Set.Demo04;

import java.util.Objects;

public class Person implements Comparable {
    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() {
        return Objects.hash(getName(), getAge());
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Person)) return false;
        Person person = (Person) o;
        return getAge() == person.getAge() && Objects.equals(getName(), person.getName());
    }

    //比较规则，先按姓名比，再按年龄比
    @Override
    public int compareTo(Person o) {
        int n1 = this.getName().compareTo(o.getName());
        int n2 = this.getAge() - o.getAge();
        return n1 == 0 ? n2 : n1;
    }
}

案例

treeset 案例要求：字符串长度排序，同长度再按字母顺序

package Collection.Set.Demo04;
import java.util.Comparator;
import java.util.TreeSet;
/**
 * treeset  案例要求：字符串长度排序，同长度再按字母顺序
 *
 * @author liu
 */
public class Demo02 {
    public static void main(String[] args) {
        //创建集合并顶规则
        TreeSet treeSet = new TreeSet<>(new Comparator() {
            @Override
            public int compare(String o1, String o2) {
                int n1 = o1.length() - o2.length();
                int n2 = o1.compareTo(o2);
                return n1 == 0 ? n2 : n1;
            }
        });
        //添加元素
        treeSet.add("xian");
        treeSet.add("aiaa");
        treeSet.add("nanjing");
        treeSet.add("helloWorld");
        treeSet.add("list");
        treeSet.add("lisa");

        System.out.println(treeSet);
    }
}