指定字符串中指定部分进行反转 abcdefg-->abcgfed

public static String reverseString(String str,int start,int end){
char [] ch = str.toCharArray();//字符串-->字符数组
return reverseArray(ch,start,end);
}

public static String reverseArray(char [] ch,int start,int end){
for(int i = start,j = end;i < j;i++,j--){
char temp = ch[i];
ch[i] = ch[j];
ch[j] = temp;
}
//字符数组-->字符串
return new String(ch);
}