Read N Characters Given Read4 II

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;
    }
}