将一个英文句子反转， e.g. much. very you love I => I love you very much.

import java.util.Stack;

import java.util.StringTokenizer;

/**

* 将一个英文句子反转， e.g. much. very you love I => I love you very much.

*/

public class WordsReverse {

// spilt StringBuilder

public static String reverse1(String str) {

if (str == null || str.trim().equals("")) {

return str;

}

StringBuilder re = new StringBuilder();

String[] words = str.split(" ");

for (int length = words.length, i = length - 1; i >= 0; i--) {

re.append(words[i]);

if (i != 0) {

re.append(" ");

}

}

return re.toString();

}

// charAt StringBuilder

public static String reverse2(String str) {

if (str == null || str.trim().equals("")) {

return str;

}

StringBuilder re = new StringBuilder(str.length());

int pos = 0;

for (int length = str.length(), i = 0; i < length; i++) {

char ch = str.charAt(i);

if (ch == ' ') {

pos = 0;

}

re.insert(pos, ch);

if (ch != ' ') {

pos++;

}

}

return re.toString();

}

// StringTokenizer Stack StringBuilder

public static String reverse3(String str) {

if (str == null || str.trim().equals("")) {

return str;

}

StringTokenizer token = new StringTokenizer(str, " ");

Stack stack = new Stack();

while (token.hasMoreElements()) {

stack.push(token.nextToken());

}

StringBuilder re = new StringBuilder(str.length());

for (int length = stack.size(), i = 0; !stack.isEmpty(); i++) {

re.append(stack.pop());

if (i != length - 1) {

re.append(" ");

}

}

return re.toString();

}

// charAt Stack StringBuilder

public static String reverse4(String str) {

if (str == null || str.trim().equals("")) {

return str;

}

Stack stack = new Stack();

final int RESET = -1;

int start = RESET;

for (int length = str.length(), i = 0; i < length; i++) {

char ch = str.charAt(i);

if (ch != ' ' && start == RESET) {// word started

start = i;

} else if ((ch == ' ') && start != RESET) {// find word

stack.push(str.substring(start, i));

start = RESET;

} else if ((i == length - 1) && start != RESET) {// find word

stack.push(str.substring(start, i + 1));

start = RESET;

}

}

StringBuilder re = new StringBuilder(str.length());

for (int length = stack.size(), i = 0; !stack.isEmpty(); i++) {

re.append(stack.pop());

if (i != length - 1) {

re.append(" ");

}

}

return re.toString();

}

public static void main(String[] args) {

long beginTime = System.currentTimeMillis();

System.out.println(reverse1(null) + "|");

System.out.println(reverse1("") + "|");

System.out.println(reverse1(" ") + "|");

System.out.println(reverse1(" ") + "|");

System.out.println(reverse1(" ") + "|");

System.out.println(reverse1(" BB ") + "|");

System.out.println(reverse1(" AA BB ") + "|");

System.out.println(reverse1("ABC is a pig.") + "|");

System.out.println(reverse1(" ABC is a pig. ") + "|");

reverse1(longString);

System.out.println("spend time:"

+ (System.currentTimeMillis() - beginTime));

beginTime = System.currentTimeMillis();

System.out.println(reverse2(null) + "|");

System.out.println(reverse2("") + "|");

System.out.println(reverse2(" ") + "|");

System.out.println(reverse2(" ") + "|");

System.out.println(reverse2(" ") + "|");

System.out.println(reverse2(" BB ") + "|");

System.out.println(reverse2(" AA BB ") + "|");

System.out.println(reverse2("ABC is a pig.") + "|");

System.out.println(reverse2(" ABC is a pig. ") + "|");

reverse2(longString);

System.out.println("spend time:"

+ (System.currentTimeMillis() - beginTime));

beginTime = System.currentTimeMillis();

System.out.println(reverse3(null) + "|");

System.out.println(reverse3("") + "|");

System.out.println(reverse3(" ") + "|");

System.out.println(reverse3(" ") + "|");

System.out.println(reverse3(" ") + "|");

System.out.println(reverse3(" BB ") + "|");

System.out.println(reverse3(" AA BB ") + "|");

System.out.println(reverse3("ABC is a pig.") + "|");

System.out.println(reverse3(" ABC is a pig. ") + "|");

reverse3(longString);

System.out.println("spend time:"

+ (System.currentTimeMillis() - beginTime));

beginTime = System.currentTimeMillis();

System.out.println(reverse4(null) + "|");

System.out.println(reverse4("") + "|");

System.out.println(reverse4(" ") + "|");

System.out.println(reverse4(" ") + "|");

System.out.println(reverse4(" ") + "|");

System.out.println(reverse4(" BB ") + "|");

System.out.println(reverse4(" AA BB ") + "|");

System.out.println(reverse4("ABC is a pig.") + "|");

System.out.println(reverse4(" ABC is a pig. ") + "|");

reverse4(longString);

System.out.println("spend time:"

+ (System.currentTimeMillis() - beginTime));

}

static String t = "das dasd sad asd sdsa as as dasd sdasdad adasdsd as dsa d asd sa d asd as das d sad asdd as das d asd as das d asd as d sad a sd asd as da sda ds ";

static String longString = t + t + t + t + t + t + t + t + t + t + t + t

+ t + t + t + t + t + t + t + t + t + t + t + t + t + t + t + t + t

+ t + t + t + t + t + t + t + t + t + t + t + t + t + t + t + t + t;

}

输出：

null|

|

|

|

|

BB  |

BB AA |

pig. a is  ABC|

pig. a is  ABC |

spend time:14

null|

|

|

|

|

BB  |

BB AA |

pig. a is  ABC|

pig. a is  ABC |

spend time:8

null|

|

|

|

|

BB|

BB AA|

pig. a is ABC|

pig. a is ABC|

spend time:5

null|

|

|

|

|

BB|

BB AA|

pig. a is ABC|

pig. a is ABC|

spend time:3

20120425写的新方法：

import java.util.Stack;

public class Demo {

/**

* 反转字符串的单词顺序

*/

public static void main(String[] args) {

String str = "hello world is demo";

System.out.println(reverse(str));

}

static String reverse(String str) {

StringBuilder sb = new StringBuilder(str.length());

Stack stack = new Stack();

int i = str.length() - 1;

while (i >= 0) {//从尾部开始遍历

char ch = str.charAt(i);

if (ch == ' ') {//遇到空格，则说明找到单词，将单词取出

while (!stack.isEmpty()) {

sb.append(stack.pop());

}

sb.append(ch);

} else {//遇到非空格，则字符入栈

stack.push(ch);

}

i--;

}

while (!stack.isEmpty()) {

sb.append(stack.pop());

}

return sb.toString();

}

}