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@Yuiki

Yuiki/Main.java

Created Jul 12, 2015
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ArrayList処理と配列処理の実行時間の比較。
public class Main {
private final int quantity = 1000000;
// frequencyの値を増やすほど精度が増す。
private final int frequency = 10;
// コンストラクタで要素数指定。
private final List<Integer> list = new ArrayList<>(quantity);
private final int[] array = new int[quantity];
public static void main(String[] args) {
Main main = new Main();
List<Long> arrayMeanValue = new ArrayList<>();
List<Long> arrayListMeanValue = new ArrayList<>();
System.out.println("要素数" + main.quantity + "で処理を開始します。");
for (int i = 0; i < main.frequency; i++) {
System.out.println("配列処理(" + i + 1 + "回目)を開始します。");
long executionTimeArray = main.measureTime(main::useArray, main.quantity);
System.out.println("終了しました。");
arrayMeanValue.add(executionTimeArray);
System.out.println("ArrayList処理(" + i + 1 + "回目)を開始します。");
long executionTimeList = main.measureTime(main::useArrayList, main.quantity);
System.out.println("終了しました。");
arrayListMeanValue.add(executionTimeList);
}
long arrayMeanValueAve = main.calcAverage(arrayMeanValue);
long arrayListMeanValueAve = main.calcAverage(arrayListMeanValue);
System.out.println("配列処理の実行平均時間:" + arrayMeanValueAve/ 1000000 + "ms");
System.out.println("ArrayList処理の実行時間:" + arrayListMeanValueAve / 1000000 + "ms");
System.out.println("配列処理のほうが" + main.compareValue(arrayMeanValueAve, arrayListMeanValueAve) / 1000000 + "ms速いです。");
}
private void useArray(int quantity) {
for (int i = 0; i < quantity; i++) {
array[i] = i;
}
Arrays.stream(array).forEach(System.out::println);
Arrays.fill(array, 0);
}
private void useArrayList(int quantity) {
for (int i = 0; i < quantity; i++) {
list.add(i);
}
list.stream().forEach(System.out::println);
list.clear();
}
private long calcAverage(List<Long> list) {
long sum = 0;
for (long value : list) {
sum += value;
}
return sum / list.size();
}
private long compareValue(long a, long b) {
return a - b;
}
private <T> long measureTime(Consumer<T> proc, T arg) {
long start = System.nanoTime();
proc.accept(arg);
return System.nanoTime() - start;
}
}
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