How to read a complete Unicode code point as String?

Question

I tried this so far:

public String readchar (Reader input) throws java.io.IOException
{
  int i16 = input.read(); // UTF-16 as int
  if (i16 == -1) return null;
  char c16 = (char)i16; // UTF-16
  if (Character.isHighSurrogate(c16)) {
    int low_i16 = input.read(); // low surrogate UTF-16 as int
    if (low_i16 == -1)
      throw new java.io.IOException ("Can not read low surrogate");
    char low_c16 = (char)low_i16;
    int codepoint = Character.toCodePoint(c16, low_c16);
    return new String (Character.toChars(codepoint));
  }
  else 
    return Character.toString(c16);
}

But it contains unsafe casts. I have no idea how to avoid them. Is it possible?

Answer 1

The javadoc of the read method states:

Returns: The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached

The char primative is "a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive)."

(emphasis mine)

It would appear that your two C-style casts are safe.