使用Arrays类:其中的sort()使用的是“经过调优的快速排序法”
String[] data = {"1", "4", "3", "2"};
System.out.println(Arrays.toString(data)); // [1, 4, 3, 2]
Arrays.sort(data);
System.out.println(Arrays.toString(data)); // [1, 2, 3, 4]
Arrays.sort(T[] array, Comparator super T> comparator)
使用自定义比较器,对数组元素进行排序(串行排序)
String[] data = {"1", "4", "3", "2"};
System.out.println(Arrays.toString(data)); // [1, 4, 3, 2]
// 实现降序排序,返回-1放左边,1放右边,0保持不变
Arrays.sort(data, (str1, str2) -> {
if (str1.compareTo(str2) > 0) {
return -1;
} else {
return 1;
}
});
System.out.println(Arrays.toString(data)); // [4, 3, 2, 1]
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));
}
public 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));
}
public 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));
}
@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 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");
}
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.
public static void main(String args[])
{
int[] Arr = {1,2,3,4,5,6,7,8,9};
Random random = new Random();
for (int i=0;i<Arr.length;i++ ){
int p = random.nextInt(i+1);//该方法的作用是生成一个随机的int值,该值介于[0,n)的区间
int tmp = Arr[i];
Arr[i]=Arr[p];
Arr[p]=tmp;
}
for (int i:Arr
) {
System.out.println(i+"");
}
}