java Map

佚名 6年前 (2019-04-26) 随笔 1800人围观抢沙发百度已收录

package cn.sxt.map;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Test01 {
    public static void main(String[] args) {
        //初始化，1W次赋值
        Map<Integer,Integer>map = new HashMap<Integer,Integer>();
        for(int i=0; i<100000; i++) {
            map.put(i, i);
        }
        /**增强for循环，keySet迭代**/
        long start = System.currentTimeMillis();
        for(Integer key: map.keySet()) {
            map.get(key);
        }
        long end = System.currentTimeMillis();
        System.out.println("增强for循环，keySet迭代->"+(end-start)+"ms");
        
        /** 迭代器，keySet迭代 **/
        start = System.currentTimeMillis();
        Iterator<Integer> iterator = map.keySet().iterator();
        Integer key;
        while(iterator.hasNext()) {
            key = iterator.next();
            map.get(key);
        }
        
        end = System.currentTimeMillis();
        
        System.out.println("迭代器，keySet迭代->"+(end-start)+"ms");
        
        /** 迭代器，entrySet迭代 **/
        start = System.currentTimeMillis();
        Iterator<Map.Entry<Integer, Integer>> iterator1 = map.entrySet().iterator();
        Map.Entry<Integer, Integer> entry;
        while(iterator1.hasNext()) {
            entry = iterator1.next();
            entry.getKey();
            entry.getValue();
        }
        end = System.currentTimeMillis();
        System.out.println("迭代器，entrySet迭代->"+(end-start) + "ms");
    
    }
}