如何用BufferedReader + StringTokenizer实现hasNext()方法？

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class CustomScanner {
    private BufferedReader reader;
    private StringTokenizer tokenizer;

    public CustomScanner(InputStream inputStream) {
        reader = new BufferedReader(new InputStreamReader(inputStream));
        tokenizer = new StringTokenizer("");
    }

    public boolean hasNext() throws IOException {
        while (!tokenizer.hasMoreTokens()) {
            String line = reader.readLine();
            if (line == null) {
                return false;
            }
            tokenizer = new StringTokenizer(line);
        }
        return true;
    }

    public String next() throws IOException {
        if (hasNext()) {
            return tokenizer.nextToken();
        }
        return null;
    }

    public void close() throws IOException {
        reader.close();
    }
}