字符串的反转

jdk的方法：

1 String str = “abcdef”; 
2 str = new StringBuilder(str).reverse().toString();

自己实现：

 1 public class StringDemo{
 2     public static void main(String[] args) {
 3         System.out.println(reverse("Hello World!"));//!dlroW olleH
 4     }
 5     public static String reverse(String str){
 6        char [] arrs = str.toCharArray();
 7         char temp = ' ';
 8         for(int i = 0, j = arrs.length-1; i < j; i++,j--){
 9             temp = arrs[i];
10            arrs[i] = arrs[j];
11            arrs[j] = temp;
12         }
13         StringBuilder sb = new StringBuilder();
14         for(char s : arrs){
15            sb.append(s);
16         }
17         return sb.toString();
18     }
19 }
20 
21 public void reverse2(final String str){
22    char [] chars = str.toCharArray();
23    StringBuilder sb = new StringBuilder();
24    for(int i = chars.length-1;i>0; i--){
25       sb.append(char[i]);
26    }
27    return sb.toString();
28 }

 

* “I love china”, 把字符反转后变成 “china love I”
方法一：一个字符一个字符的换

 1 public class StringReverse {
 2     
 3     public void swap(char[] arr, int begin, int end) {
 4         while(begin < end) {
 5             char temp = arr[begin];
 6             arr[begin] = arr[end];
 7             arr[end] = temp;
 8             begin++;
 9             end--;
10         }
11     }
12     public String swapWords(String str) {
13         char[] arr = str.toCharArray();
14         swap(arr, 0, arr.length - 1);
15         int begin = 0;
16         for (int i = 1; i < arr.length; i++) {
17             if (arr[i] == ' ') {
18                 swap(arr, begin, i - 1);
19                 begin = i + 1;
20             }
21         }
22 
23         return new String(arr);
24     }
25     public static void main(String[] args) {
26         String str = "I love java";
27         System.out.println(new StringReverse().swapWords(str));
28     }
29 }


方法二：（利用jdk提供的方法）

 1 public class Main {
 2     public static void main(String[] args) {
 3         Scanner sc = new Scanner(System.in);
 4         String str = sc.nextLine();
 5         String[] sArr = str.split(" ");//I love java
 6         List<String> list = Arrays.asList(sArr);
 7         Collections.reverse(list);
 8         for(String word:list){
 9             System.out.print(word+" ");
10         }
11     }
12 }

方法3：一个单词一个单词地换

 1 public class StringDemo{
 2     public static void main(String[] args) {
 3         System.out.println(reverse("Hello World!"));//World! Hello
 4     }
 5     public static String reverse(String str){
 6     String [] arrs = str.split(" ");
 7         String temp = "";
 8         for(int i = 0, j = arrs.length-1; i < j; i++, j--){
 9             temp = arrs[i];
10            arrs[i] = arrs[j];
11            arrs[j] = temp;
12         }
13         StringBuilder sb = new StringBuilder();
14         for(String s : arrs){
15            sb.append(s).append(" ");
16         }
17       return sb.toString();
18     }
19 }

 

posted @ 2015-09-07 19:06  yweihainan  阅读(195)  评论(0)  编辑  收藏  举报