Java 数组元素倒序的三种方式(小结)

2019-11-26 08:32:47

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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: