@org.junit.jupiter.api.Test
public void compareArrayListAndHashMapAndSet1(){
Map<Long, Long> map = new HashMap<>();
for (int i = 0; i < 1000_0000; i++) {
map.put(i+1L, i+1L);
}
long start = System.currentTimeMillis();
for (int i = 0; i < 1000_0000; i++) {
boolean b = map.containsKey(i + 1L);
}
long end = System.currentTimeMillis();
System.out.println("1000w元素 map耗时:" + (end-start));
List<Long> list = new ArrayList<>();
for (int i = 0; i < 10_0000; i++) {
list.add(i+1L);
}
long start2 = System.currentTimeMillis();
for (int i = 0; i < 10_0000; i++) {
boolean b = list.contains(i + 1L);
}
long end2 = System.currentTimeMillis();
System.out.println("10W元素 list耗时:" + (end2-start2));
Set<Long> set = new HashSet<>();
for (int i = 0; i < 1000_0000; i++) {
set.add(i+1L);
}
long start3 = System.currentTimeMillis();
for (int i = 0; i < 1000_0000; i++) {
boolean b = set.contains(i + 1L);
}
long end3 = System.currentTimeMillis();
System.out.println("1000w元素 set耗时:" + (end3-start3));
}
结论:
map和set因为底层用的hash表,所以差距不大;
因为我只存一个Long类型的id,所以我选择了Set
1000w元素时的List速度太慢,再见了!
推荐key,value选择HashMap;
网上找了个图:
连接在这:(尊重原创)
https://blog.csdn.net/high2011/article/details/106742629