将数组元素反转有多种实现方式,这里介绍常见的三种.

直接数组元素对换

@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存入和取出的顺序是一样的,可以利用这里特性暂时存储数组元素.

@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工具类

@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)); // 这种方式仅针对引用类型,对于基本类型如: // char[] cs = {'a','b','c','g','d'}; // 应该定义或转换成对应的引用类型: // Character[] cs = {'a','b','c','g','d'}; Collections.reverse(Arrays.asList(strings)); System.out.println("\t" + Arrays.toString(strings));}

速度测试:

@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); }}/** * 记录操作执行总时间. * * @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");}

测试结果:

使用Collections和Arrays工具类: 12 ms
使用ArrayList: 7 ms
直接数组元素对换: 4 ms
当数据量越来越大时,使用ArrayList的方式会变得很慢.
直接使用数组元素对换,总是最快完成.

总结: 使用Collections和Arrays工具类反转数组元素更简单,但是在原数组上操作时速度更快,并且占用最少的内存.

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