Java 數組元素倒序的三種方式

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將數組元素反轉有多種實現方式,這裡介紹常見的三種.

• 直接數組元素對換

@Testpublic void testReverseSelf() throws Exception { System.out.println("use ReverseSelf"); String[] strings = { "ramer", "jelly", "bean", "cake" }; System.out.println("\t" + Arrays.toString(strings)); for (int start = 0, end = strings.length - 1; start < end; start++, end--) { String temp = strings[end]; strings[end] = strings[start]; strings[start] = temp; } System.out.println("\t" + Arrays.toString(strings));}

• 使用ArrayList: ArrayList存入和取出的順序是一樣的,可以利用這裡特性暫時儲存數組元素.

@Testpublic void testArrayList() throws Exception { System.out.println("use ArrayList method"); String[] strings = { "ramer", "jelly", "bean", "cake" }; System.out.println("\t" + Arrays.toString(strings)); List<String> list = new ArrayList<>(strings.length); for (int i = strings.length - 1; i >= 0; i--) { list.add(strings[i]); } strings = list.toArray(strings); System.out.println("\t" + Arrays.toString(strings));}

• 使用Collections和Arrays工具類

@Testpublic void testCollectionsReverse() throws Exception { System.out.println("use Collections.reverse() method"); String[] strings = { "ramer", "jelly", "bean", "cake" }; System.out.println("\t" + Arrays.toString(strings)); // 這種方式僅針對參考型別,對於基本類型如: // char[] cs = {‘a‘,‘b‘,‘c‘,‘g‘,‘d‘}; // 應該定義或轉換成對應的參考型別: // Character[] cs = {‘a‘,‘b‘,‘c‘,‘g‘,‘d‘}; Collections.reverse(Arrays.asList(strings)); System.out.println("\t" + Arrays.toString(strings));}

• 速度測試:

@Testpublic void testTimeDuration() throws Exception { recordTime(ArrayReverse.class,"testCollectionsReverse"); recordTime(ArrayReverse.class,"testArrayList"); recordTime(ArrayReverse.class,"testReverseSelf");}private static String[] strings = new String[1000000];{ for (int i = 0; i < 1000000; i++) { strings[i] = String.valueOf(i); }}/** * 記錄操作執行總時間. * * @param <T> the generic type * @param clazz the clazz * @param methodName the method name */public <T> void recordTime(Class<T> clazz, String methodName) { long start = System.currentTimeMillis(); System.out.println("start: " + start); Method[] declaredMethods = clazz.getDeclaredMethods(); for (Method method : declaredMethods) { String name = method.getName(); if (name.equals(methodName)) { try { method.invoke(clazz.newInstance()); } catch (Exception e) { e.printStackTrace(); } } } long end = System.currentTimeMillis(); System.out.println("end: " + end); System.out.println("duration: " + (end - start) + " ms");}

• 測試結果:

  使用Collections和Arrays工具類: 12 ms
  使用ArrayList: 7 ms
  直接數組元素對換: 4 ms
  當資料量越來越大時,使用ArrayList的方式會變得很慢.
  直接使用數組元素對換,總是最快完成.

• 總結: 使用Collections和Arrays工具類反轉數組元素更簡單,但是在原數組上操作時速度更快,並且佔用最少的記憶體.

Java 數組元素倒序的三種方式