四、set集合
无序、无下标、元素不可重复
1、hashSet【重点】
== 数组+链表+红黑树==
基于hashcode计算元素存储位置
当哈希吗一样的时候，调用equals，如果为true,拒接存入
package com.zheng.demo3;
import java.util.HashSet;
import java.util.Iterator;
public class MySet {
public static void main(String[] args) {
//创建集合框架
HashSet<String> set = new HashSet<>();
//添加数据
set.add("1-小红");
set.add("2-小明");
set.add("3-小白");
set.add("4-小黑");
set.add("5-小红");
set.add("1-小红");
//迭代器迭代集合元素 遍历
Iterator<String> iterator = set.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
}
}
实体类
package com.zheng.demo3;
public class School {
private int id;
private String name;
public School() {
}
public School(int id, String name) {
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "School{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}package com.zheng.demo3;
import java.util.HashSet;
import java.util.Iterator;
public class TestSet {
public static void main(String[] args) {
//1、创建集合容器
HashSet<School> schools = new HashSet<>();
//创建对象
School school1 = new School(1, "清华大学");
School school2 = new School(2, "北京大学");
School school3 = new School(3, "浙江大学");
//3、放入集合
schools.add(school1);
schools.add(school2);
schools.add(school3);
schools.add(new School(2,"北京大学"));
//4、遍历
Iterator<School> iterator = schools.iterator();
while (iterator.hasNext()){
School school=iterator.next();
System.out.println(school);
}
}
}
2、TreeSet
存储结构：红黑树
要实现comparable接口，重写里边的方法，返回0代表元素重复
元素不重复
元素自动排序
package com.zheng.demo3;
import java.util.Iterator;
import java.util.TreeSet;
public class MyTree {
public static void main(String[] args) {
//1、创建一个集合
TreeSet treeSet = new TreeSet();
//2、加入元素
treeSet.add(1);
treeSet.add(3);
treeSet.add(2);
treeSet.add(4);
treeSet.add(3);
//3、迭代遍历
Iterator iterator = treeSet.iterator();
while (iterator.hasNext()) {
int i = (int) iterator.next();
System.out.println(i);
}
}
}
TreeSet案例：排列字符串的顺序
package com.zheng.demo3;
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;
public class MyTreeSet {
public static void main(String[] args) {
//匿名内部类
TreeSet<String> set = new TreeSet<>(new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
int n1 = o1.length() - o2.length();
int n2 = o1.compareTo(o2);
return n1 == 0 ? n2 : n1;
}
});
set.add("he");
set.add("hhhhh");
set.add("jdjdjkdkk");
set.add("djdj");
Iterator<String> iterator = set.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
}
}
comparator：定制比较器
