[Set]——逻辑梳理

public class MySet {
HashMap map;
private static final Object PRESENT=new Object();
public MySet(){
map=new HashMap();
}
public int size(){
return map.size();
}
public void add(Object o){
map.put(o,PRESENT);
//set的不可重复就是利用了map里面键对象的不可重复！
}
public static void main(String[] args) {
MySet s = new MySet();
s.add("aaa");
s.add(new String("aaa"));
s.add(new String("aa2"));
System.out.println(s.size());
}
}