自定义HashSet

 HashSet其实就是简化版的HashMap

import java.util.HashMap;

/**
 * 自定义HashSet其实就是简化版的HashMap
 * @author Administrator
 *
 */
public class MyHashSet00 {
	HashMap map;
	private final Object PRESENT = new Object();
	public MyHashSet00() {
		map = new HashMap();
	}
	public void add(Object o) {
		map.put(o, PRESENT);
	}
	public int size() {
		return map.size();
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append('[');
		for(Object key:map.keySet()) {
			sb.append(key+",");
		}
		sb.setCharAt(sb.length()-1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyHashSet00 s = new MyHashSet00();
		s.add("aaa");
		s.add("bbb");
		s.add("ccc");
		System.out.println(s);
	}
	
}