阿里规约中"集合初始化时应指定初始值大小"的校验

作者对阿里公约中对集合需要给定初始化值对性能的测试:

测试代码:

/**
 * @Author: 徐建华
 * @Date: 2018/9/21 14:07
 */
public class HashMapTest {
    public static void main(String[] args) {
        Long times = 0L;
        for (int j = 0; j < 10; j++) {
            HashMap map2 = new HashMap<>(500);
            long startMapTime2 = System.currentTimeMillis();
            for (int i = 0; i < 1000000000; i++) {
                map2.put("map", "map");
            }
            long endMapTime2 = System.currentTimeMillis();
            Long time = endMapTime2 - startMapTime2;
            times = times + time;
            System.out.println("加了初始容量的时间:" + j + "次" + time);
        }
        System.out.println("加了初始容量的平均时间:" + (times / 10));

        System.out.println("=======================================");

        Long times1 = 0L;
        for (int j1 = 0; j1 < 10; j1++) {
            HashMap map3 = new HashMap<>();
            long startMapTime2 = System.currentTimeMillis();
            for (int i = 0; i < 1000000000; i++) {
                map3.put("map", "map");
            }
            long endMapTime2 = System.currentTimeMillis();
            Long time = endMapTime2 - startMapTime2;
            times1 = times1 + time;
            System.out.println("没加初始容量的时间:" + j1 + "次" + time);
        }
        System.out.println("没加初始容量的平均时间:" + (times1 / 10));
    }
}

测试结果:

测试结论:

确实快,但是要求在数据量很大的情况下才会效果明显,需不要做这块的优化,可以跟据自己的业务要求做调整.