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集合 set接口
2022-08-10 05:32:00 【hagong9】
目录
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
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