给定字符串，删除开始和结尾处的空格，并将中间的多个连续的空格合并成一个

<pre name="code" class="java">package com.one;

public class DeleteExtraSpace {
/**
* 题目：给定字符串，删除开始和结尾处的空格，并将中间的多个连续的空格合并成一个。 方法1.用已有的String类的trim和replaceAll方法
* 方法 2.全部用正则表达式，这个我不熟 方法 3.“重新发明轮子”，从头遍历一次
*/
public static void main(String[] args) {

String strs = "  hello    world   !  ";
String str2 = strs.trim().replaceAll(" +", " ");
System.out.println(str2 + ",length2=" + str2.length());

String str3 = deleteExtraSpace(strs);
System.out.println(str3 + ",length3=" + str3.length());

System.out.println(str2.equals(str3));
System.out.println("=========================");
}

public static String deleteExtraSpace(String str) {
if (str == null) {
return null;
}
if (str.length() == 0 || str.equals(" ")) {
return new String();
}
char[] oldStr = str.toCharArray();
int len = str.length();
char[] tmpStr = new char[len];
boolean keepSpace = false;
int j = 0;// the index of new string
for (int i = 0; i < len; i++) {
char tmpChar = oldStr[i];
if (oldStr[i] != ' ') {
tmpStr[j++] = tmpChar;
keepSpace = true;
} else if (keepSpace) {
tmpStr[j++] = tmpChar;
keepSpace = false;
}
}
//判断结尾空格
// unlike c/c++,no "\0" at the end of a string. So,do the copy again...
int newLen = j;
if (tmpStr[j - 1] == ' ') {
newLen--;
}
char[] newStr = new char[newLen];
for (int i = 0; i < newLen; i++) {
newStr[i] = tmpStr[i];
}
return new String(newStr);
}
}