在一个字符串中把大写字母放到字符串中小写字母的后面(不能改变字母的相对位置)

public void swapCharacter(char[] ch){
if(null==ch||0==ch.length)return;
int p1 =ch.length-1;
int p2 =ch.length-1;
while(p1>=0){
while(p1>=0&&ch[p1]>='a'&&ch[p1]<='z'){
p1--;
}
int index = p1;
while(index>=0&&index!=p2){
char t = ch[index];
ch[index] = ch[index+1];
ch[index+1] = t;
index++;
}
p2--;
p1--;
}
}