请求各位大吓告诉我一下为什么会报异常

Question

package IODemo;
import java.io.*;
import java.util.*;
public class TestFileOBJ {
public void FileInformation(File f){
System.out.println("getName="+f.getName());
System.out.println("getPath="+f.getPath());
System.out.println("getAbsolutePath="+f.getAbsolutePath());
System.out.println("getParent="+f.getParent());
System.out.println("length="+f.length());
System.out.println("lastModified="+new Date(f.lastModified()));
}
public void DirectoryInformation(File d){
System.out.println("Dir.getName="+d.getName());
System.out.println("Dir.getParent="+d.getParent());

    int i=0;
    String it[]=d.list();//列出文件与子目录
    while(i<it.length){
        System.out.println("Files="+it[i]);
        i++;
    }
}
public static void main(String[] args){
    File f=new File("E://IOdemo","Fileln.java");
    File d=new File("E://IOdemo//IOdemo");
    File d1=new File("E://IOdemo//Demo01");
    TestFileOBJ fo=new TestFileOBJ();
    System.out.println("File.information:"+f.getAbsolutePath());
    System.out.println("================================");
    fo.FileInformation(f);
    System.out.println("================================");
    System.out.println("Directory information:E:\\javalianxi\\Bark");
    System.out.println("================================");
    fo.FileInformation(d);
    fo.DirectoryInformation(d);
    System.out.println("================================");
    d1.mkdir();
}

}

Answer 1

19行，空对象，调试就知道了