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();

}