去掉字符串中的多余空格

/**
* 把字符串“they are people” 改写为“they are people”，在原字符串上修改
*
*/
public class DeleteBlank {

public static String modifyStr(StringBuilder sbi) {
if (sbi == null) {
return null;
}
int nStart = 0;
int p = 0;
int q = 0;
int len = sbi.length();
while (p < len && q < len) {
while (p < len && sbi.charAt(p) != ' ') {
sbi.setCharAt(nStart++, sbi.charAt(p));
p++;
}
if (p < len) {
q = p + 1;
sbi.setCharAt(nStart++, ' ');
if (sbi.charAt(q) != ' ') {
p++;
} else {
while (q < len && sbi.charAt(q) == ' ')
q++;
if (q < len) {
p = q;
}
}

}
}
if (nStart < len - 1) {
sbi.delete(nStart, len);
}
return sbi.toString();
}

public static void main(String[] args) {
StringBuilder sbi = new StringBuilder("they    are   people   abc de");
System.out.print(modifyStr(sbi));
}

}