Read N Characters Given Read4 II - Call multiple times

The API: int read4(char *buf) reads 4 characters at a time from a file.

The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.

By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.

Note:
The read function may be called multiple times.

 /* The read4 API is defined in the parent class Reader4.
       int read4(char[] buf); */

 public class Solution extends Reader4 {
     /**
      * @param buf Destination buffer
      * @param n   Maximum number of characters to read
      * @return    The number of characters read
      */
     private char[] tmp = new char[4];
     private int tmpPoint; //indicate which position we should start reading
     private int tmpContain;//indicate how many char in the tmp buff
     public int read(char[] buf, int n) {
         int cur = 0;
         while(cur < n){
             if(tmpPoint == 0){
                 tmpContain = read4(tmp);
             }
             if(tmpContain == 0){
                 return cur;
             }
             while(cur < n && tmpPoint < tmpContain){
                 buf[cur ++] = tmp[tmpPoint ++];
             }
             tmpPoint = tmpPoint % tmpContain;
         }
         return cur;
     }
 }