IO流读取文件内容时，出现空格的问题（未找到原因）

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;

public class TestFileWriter {
	public static void main(String[] args) throws IOException {
		File i = new File("D:\\Huang\\123.txt");
		FileReader r = new FileReader(i);
		FileWriter w = new FileWriter("D:\\Huang\\abcd.txt");
		StringBuilder sb = new StringBuilder();
		int b = -1;
		char[] cs = new char[(int) i.length()];
		int num = 0;
		System.out.println(i.length());
		while ((b = r.read(cs)) != -1) {
			sb.append(cs);
			System.out.println((num++) + Arrays.toString(cs));
			System.out.println((num++) + String.valueOf(cs));//打印输出时   会输出空格
		}
		w.write(sb.toString());
		w.flush();
		r.close();
		w.close();

	}