java数组元素倒序的三种方法

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));}
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• 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));}
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• 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));}
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• 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");}
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• 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.