HashSet ：https://blog.fondme.cn/apidoc/jdk-1.8-google/
package learn.java.cn.collection;
import java.util.HashMap;
import java.util.HashSet;
public class MyHashSet {
/*
* ###################
* 自己实现HashSet
*/
private static final Object PRESENT=new Object();
HashMap map;
public MyHashSet()
{
map=new HashMap();
}
public int size()
{
return map.size();
}
public void add(Object e)
{
map.put(e, PRESENT);
}
public static void main(String[] args) {
MyHashSet s=new MyHashSet();
s.add("王尚权");
s.add("小静");
s.add(new String("王尚权"));
System.out.println(s.size());
/*
* ###################
* 测试java.util 中封装 的HashSet
*/
HashSet hs=new HashSet();
HashSet sh=new HashSet();
hs.add("小静");
hs.add("王尚权");
sh.add("李白");
sh.add("杨幂");
hs.add(sh);//将sh 对象加入到hs，hs.size()增大1
System.out.println(hs.contains(sh));//结果为真
System.out.println(hs.contains("杨幂"));//结果为假
hs.addAll(sh);//将sh的elements加入到hs,hs.size增大2
System.out.println(hs.contains("杨幂"));//结果为真
System.out.println(hs.isEmpty());
System.out.println(hs.size());
hs.add("李白");//不可重复性
System.out.println(hs.size());//
}
}