理解java容器底层原理--手动实现HashSet

HashSet的底层其实就是HashMap，换句话说HashSet就是简化版的HashMap。
直接上代码：

package com.xzlf.collection2;

import java.util.HashMap;

public class MyHashSet<E> {
	
	HashMap<E, Object> map;
	private static final Object PRESENT = new Object();
	
	public MyHashSet() {
		map = new HashMap<E, Object>();
	}
	
	public void add(E key) {
		map.put(key, PRESENT);
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		for (E k : map.keySet()) {
			sb.append(k + ",");
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	public static void main(String[] args) {
		MyHashSet<String> set = new MyHashSet<String>();
		set.add("aa");
		set.add("bb");
		set.add("cc");
		System.out.println(set);
	}
}

运行测试：