您可以自己测试它,但删除和重新创建数组大致相同。
但是,它有两个缺点
- 它会导致您的 CPU 数据缓存滚动,从而降低其有效性。
- 它使触发 GC 的可能性更大,尤其是如果您经常这样做,这会暂停系统或减慢它的速度(如果它是并发的)
我更喜欢重用数组,不是因为它是最快的,而是它对应用程序的其余部分影响最小。
for (int size = 16; size <= 16* 1024; size *= 2) {
int count1 = 0, count1b = 0,count2 = 0;
long total1 = 0, total1b = 0, total2 = 0;
for (long i = 0; i < 10000000000L; i += size) {
long start = System.nanoTime();
long[] longs = new long[size];
if (longs[0] + longs[longs.length - 1] != 0)
throw new AssertionError();
long mid = System.nanoTime();
long time1 = mid - start;
Arrays.fill(longs, 1L);
long time2 = System.nanoTime() - mid;
count1b++;
total1b += time1;
if (time1 < 10e3) {// no GC
total1 += time1;
count1++;
}
if (time2 < 10e3) {// no GC
total2 += time2;
count2++;
}
}
System.out.printf("%s KB took on average of %,d ns to allocate, %,d ns to allocate including GCs and %,d ns to fill%n",
size * 8 / 1024.0, total1 / count1, total1b/count1b, total2 / count2);
}
印刷
0.125 KB took on average of 35 ns to allocate, 36 ns to allocate including GCs and 19 ns to fill
0.25 KB took on average of 39 ns to allocate, 40 ns to allocate including GCs and 31 ns to fill
0.5 KB took on average of 56 ns to allocate, 58 ns to allocate including GCs and 55 ns to fill
1.0 KB took on average of 75 ns to allocate, 77 ns to allocate including GCs and 117 ns to fill
2.0 KB took on average of 129 ns to allocate, 134 ns to allocate including GCs and 232 ns to fill
4.0 KB took on average of 242 ns to allocate, 248 ns to allocate including GCs and 368 ns to fill
8.0 KB took on average of 479 ns to allocate, 496 ns to allocate including GCs and 644 ns to fill
16.0 KB took on average of 1,018 ns to allocate, 1,055 ns to allocate including GCs and 1,189 ns to fill
32.0 KB took on average of 2,119 ns to allocate, 2,200 ns to allocate including GCs and 2,625 ns to fill
64.0 KB took on average of 4,419 ns to allocate, 4,604 ns to allocate including GCs and 4,728 ns to fill
128.0 KB took on average of 8,333 ns to allocate, 9,472 ns to allocate including GCs and 8,685 ns to fill
仅证明很难假设一种方法在所有情况下都比另一种方法快。
如果我把它改成long[]
一个int[]
我看到的差不多
0.125 KB took on average of 35 ns to allocate, 36 ns to allocate including GCs and 16 ns to fill
0.25 KB took on average of 40 ns to allocate, 41 ns to allocate including GCs and 24 ns to fill
0.5 KB took on average of 58 ns to allocate, 60 ns to allocate including GCs and 40 ns to fill
1.0 KB took on average of 86 ns to allocate, 87 ns to allocate including GCs and 94 ns to fill
2.0 KB took on average of 139 ns to allocate, 143 ns to allocate including GCs and 149 ns to fill
4.0 KB took on average of 256 ns to allocate, 262 ns to allocate including GCs and 206 ns to fill
8.0 KB took on average of 472 ns to allocate, 481 ns to allocate including GCs and 317 ns to fill
16.0 KB took on average of 981 ns to allocate, 999 ns to allocate including GCs and 516 ns to fill
32.0 KB took on average of 2,098 ns to allocate, 2,146 ns to allocate including GCs and 1,458 ns to fill
64.0 KB took on average of 4,312 ns to allocate, 4,445 ns to allocate including GCs and 4,028 ns to fill
128.0 KB took on average of 8,497 ns to allocate, 9,072 ns to allocate including GCs and 7,141 ns to fill