手动实现HashSet

package 容器;

import java.util.HashMap;


public class 测试16自定义实现HashSet {
	HashMap map;
	//用作一个占位使用
	private static final Object PRESENT = new Object();
	
	public 测试16自定义实现HashSet() {
		map = new HashMap();
	}
	
	public void add(Object o) {
		map.put(o, PRESENT);
	}
	
	public int size() {
		return map.size();
	}
	
	@Override
	public String toString() {	
		for (Object o : map.keySet()) {
			System.out.println(o);
		}
		return "";
	}
	
	public static void main(String[] args) {
		测试16自定义实现HashSet s1 = new 测试16自定义实现HashSet();
		s1.add("ceshi1");
		s1.add("ceshi2");
		s1.add("ceshi3");
		System.out.println(s1);
	}
	
}