Map的两种遍历方式效率记录

package com.asiainfo.kafka.consumer;

import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class test2 {
    public static void main(String[] args) {
        ConcurrentHashMap  rh = new ConcurrentHashMap<>();
        for (int i =0; i < 100; i ++){
            rh.put(String.valueOf(i), i);
        }
        long systemTime1 = System.currentTimeMillis();
        Iterator it = rh.entrySet().iterator();
        while(it.hasNext()){
            Map.Entry entry = (Map.Entry) it.next();
            String key = (String) entry.getKey();
            Object value = entry.getValue();
        }
        long systemTime2 = System.currentTimeMillis();
        System.out.println("Iterator 时间：" + systemTime2 +"-"+ systemTime1 + "=" + (systemTime2 - systemTime1));
        long systemTime3 = System.currentTimeMillis();
        rh.forEach((x, y) -> {
            String key = x;
            Object value =  y;
        });
        long systemTime4 = System.currentTimeMillis();
        System.out.println("foreach 时间：" + systemTime4 +"-"+ systemTime3 + "=" + (systemTime4 - systemTime3));
    }
}

三次执行结果：

Iterator 时间：1584691580663-1584691580662=1
foreach 时间：1584691580729-1584691580663=66

Iterator 时间：1584691605746-1584691605744=2
foreach 时间：1584691605809-1584691605746=63

Iterator 时间：1584691614774-1584691614773=1
foreach 时间：1584691614844-1584691614774=70