Problems with getting number of chars in a file

I don't understand why the first variant is working and the second is not.

BufferedReader reader = new BufferedReader(new InputStreamReader(in, charsetName));
try {            
    char[] buffer = new char[4096];
    reader.read(buffer, 0, 4096);
    return new String(buffer);
} finally {
    reader.close();
}

BufferedReader reader = new BufferedReader(new InputStreamReader(in, charsetName));
try {
    int size = 0;
    int ch=0;
    while ((ch=reader.read())!=-1){
        size++;
    }
    char[] buffer = new char[size];
    reader.read(buffer, 0, size);
    return new String(buffer);
} finally {
    reader.close();
}