我将于茫茫人海中访我唯一灵魂之伴侣；得之，我幸；不得，我命，如此而已。——徐志摩
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| private static final int COUNT = 100 * 100 * 100;
private static void timeCost() {
List<Double> list = new ArrayList<>(COUNT);
for (int i = 0; i < COUNT; i++) {
list.add(i * 1.0);
}
long start = System.nanoTime();
Double[] notEnoughArray = new Double[COUNT - 1];
list.toArray(notEnoughArray);
long middle1 = System.nanoTime();
Double[] equalArray = new Double[COUNT];
list.toArray(equalArray);
long middle2 = System.nanoTime();
Double[] doubleArray = new Double[COUNT * 2];
list.toArray(doubleArray);
long middle3 = System.nanoTime();
list.toArray(new Double[0]);
long end = System.nanoTime();
long notEnoughArrayTime = middle1 - start;
long equalArrayTime = middle2 - middle1;
long doubleArrayTime = middle3 - middle2;
long zeroArrayTime = end - middle2;
System.out.println("数组容量小于集合大小：notEnoughArrayTime：" + notEnoughArrayTime / (1000.0 * 1000.0) + " ms");
System.out.println("数组容量等于集合大小：：equalArrayTime：" + equalArrayTime / (1000.0 * 1000.0) + " ms");
System.out.println("数组容量是集合的两倍：doubleArrayTime：" + doubleArrayTime / (1000.0 * 1000.0) + " ms");
System.out.println("数组容量传入0：zeroArrayTime：" + zeroArrayTime / (1000.0 * 1000.0) + " ms");
}
|
输出结果
所以，以后尽量用toArray[new Double[doubleArray.size()]]指定刚刚好的长度
