目录

set接口基本介绍

 数组链表模拟

小练习

练习2  

LinkedHashSet

treeset

set接口基本介绍

package com.collection_.set;

import java.util.HashSet;

public class HashSet_ {
    public static void main(String[] args) {
        HashSet set = new HashSet();
        //执行add方法后会返回一个boolean值，添加成功为true 失败为false
        // 可以通过remove指定删除哪个对象，
        System.out.println(set.add("john"));//T
        System.out.println(set.add("lucy"));//T
        System.out.println(set.add("jack"));//T
        System.out.println(set.add("Rose"));//T
        System.out.println(set.add("john"));//F
        System.out.println(set);
        System.out.println("========移除john");
        set.remove("john");
        System.out.println(set);
        //重置set
        set = new HashSet();
        System.out.println(set);//set为空
        //HashSet 不能添加相同元素？
        set.add("lucy");//T
        set.add("lucy");//F
        //这里两个jack都加入的原因是它们是new出来的，本质上是两个不同的数据，只是名字恰巧都叫jack而已。
        set.add(new Dog("jack"));//T
        set.add(new Dog("jack"));//T

        set.add(new String("rose"));//T
        set.add(new String("rose"));//F

        System.out.println(set);



    }
}
class Dog{
    private String name;

    public Dog(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return name;
    }
}

 数组链表模拟

 例子

package com.collection_.set;

import java.util.HashSet;

//建立是一个数组table 大小为16，在索引为2的地方存放一个链表
public class HashSetStructure {
    public static void main(String[] args) {
        Node[] table = new Node[16];
        System.out.println(table);
        //在索引为2的地方创建结点john
        Node john = new Node("john", null);
        table[2] = john;
        //创建结点jack
        Node jack = new Node("jack", null);
        john.next = jack;//将jack挂载到john
        System.out.println(table);
        //创建结点rose
        Node rose = new Node("rose", null);
        jack.next = rose;//将rose挂载到jack后


    }
}
class Node{
    Object item;
    Node next;

    public Node(Object item, Node next) {
        this.item = item;
        this.next = next;
    }

}

结构，如果要才索引3也创建结点，步骤也一样

 HashSet底层代码

 第6点补充：元素个数到达8个就行，而不是超过8。如果元素个数到达8而table大小<64,会对table进行扩容。

小练习

package com.collection_.set;
//添加3个人，如果名字和年龄相同则判定为同一个人，就只添加一个。
import java.util.HashSet;
import java.util.Objects;

public class HashSetTest01 {
    public static void main(String[] args) {
        HashSet set = new HashSet();
        set.add(new People("张三",18));
        set.add(new People("李四",28));
        set.add(new People("李四",28));
        set.add(new People("王五",38));
        System.out.println(set);
    }
}
class People{
    private String name;
    private int age;

    @Override
    public String toString() {
        return "people{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public People(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;
    }
//ale+ins 重写equals和hashSet
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        People people = (People) o;
        return age == people.age &&
                Objects.equals(name, people.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

练习2  

package com.collection_.set;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Objects;
@SuppressWarnings("all")
public class HashSetTest02 {
    public static void main(String[] args) {
        HashSet set = new HashSet();
        set.add(new People2("张三",8000,new Mydate(2000,2,12)));
        set.add(new People2("张三",9000,new Mydate(2000,2,12)));
        set.add(new People2("李四",9000,new Mydate(2000,6,1)));
        set.add(new People2("王五",10000,new Mydate(1998,6,29)));
        Iterator iterator = set.iterator();
        while (iterator.hasNext()) {
            Object next =  iterator.next();
            System.out.println(next);
        }
    }
}
class People2{
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        People2 people2 = (People2) o;
        return Objects.equals(name, people2.name) &&
                Objects.equals(brithday, people2.brithday);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, brithday);
    }

    private String name;
    private int sal;
    private Mydate brithday;

    @Override
    public String toString() {
        return "People2{" +
                "name='" + name + '\'' +
                ", sal=" + sal +
                ", brithday=" + brithday +
                '}';
    }

    public People2(String name, int sal, Mydate brithday) {
        this.name = name;
        this.sal = sal;
        this.brithday = brithday;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getSal() {
        return sal;
    }

    public void setSal(int sal) {
        this.sal = sal;
    }

    public Mydate getBrithday() {
        return brithday;
    }

    public void setBrithday(Mydate brithday) {
        this.brithday = brithday;
    }

}
class Mydate{
    private int year;
    private int month;
    private int day;

    @Override
    public String toString() {
        return "brithday="+ year + "/" +month +"/" + day;
    }

    public Mydate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getMonth() {
        return month;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Mydate mydate = (Mydate) o;
        return year == mydate.year &&
                month == mydate.month &&
                day == mydate.day;
    }

    @Override
    public int hashCode() {
        return Objects.hash(year, month, day);
    }
}

LinkedHashSet

和HashSet差不多就是会按照添加顺序打印。

treeset

package com.collection_.set;

import java.util.Comparator;
import java.util.TreeSet;

public class TreeSet_ {
    public static void main(String[] args) {
        TreeSet treeSet = new TreeSet();
        treeSet.add("50");
        treeSet.add("38");
        treeSet.add("john");
        treeSet.add("som");
        treeSet.add("an");
        treeSet.add("tom");
        treeSet.add("ber");
        //当使用无参构造器，创建treeset时，仍然是无序的
        System.out.println(treeSet);
        //使用TreeSet提供的一个构造器，可以提供一个比较器（匿名内部类）
        //并指定排序规则
        TreeSet treeSet1 = new TreeSet(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                //调用String的compareto方法
                return ((String)o1).compareTo((String)o2);//按照ASCII码顺序排序 ASCII码长度相等后面的就添加不进去
                //return ((String)o1).length() - ((String)o2).length();//按照长度排序，就是如果长度相同（相减等于0）就不能添加进去
            }
        });
        treeSet1.add("50");
        treeSet1.add("38");
        treeSet1.add("john");
        treeSet1.add("som");
        treeSet1.add("an");
        treeSet1.add("tom");
        treeSet1.add("ber");
        System.out.println(treeSet1);
    }
}

底层代码