Java 数组元素倒序的三种方式(小结)
发布时间:2020-12-14 19:40:00 所属栏目:Java 来源:网络整理
导读: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" +
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 @Test public 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. @Test public void testArrayList() throws Exception { System.out.println("use ArrayList method"); String[] strings = { "ramer","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 @Test public void testCollectionsReverse() throws Exception { System.out.println("use Collections.reverse() method"); String[] strings = { "ramer","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','d'}; Collections.reverse(Arrays.asList(strings)); System.out.println("t" + Arrays.toString(strings)); } 速度测试: @Test public 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:
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. 以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持我们。 (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |