为什么运行时会抛出异常？

Question

import java.io.*; 
 public class Forest implements Serializable {      private Tree tree = new Tree(); 
        public static void main(String [] args) { 
            Forest f = new Forest(); 
               try {                       FileOutputStream fs = new FileOutputStream("Forest.ser"); 
                      ObjectOutputStream os = new ObjectOutputStream(fs); 
                      os.writeObject(f); 
                      os.close(); 
               } catch (Exception ex) { ex.printStackTrace(); } 
        }
        class Tree {}
 }
       

Answer 1

难道就是Forest.ser的路径没有设置，才抛出异常？

Answer 2

public class Forest implements Serializable{
     private Tree tree = new Tree(); 
     public static void main(String [] args) { 
      Forest f = new Forest (); 
           try {                    FileOutputStream fs = new FileOutputStream("D:\\Forest.ser"); 
                   ObjectOutputStream os = new ObjectOutputStream(fs); 
                   os.writeObject(f); 
                   os.close(); 
           } catch (Exception ex) { ex.printStackTrace(); } 
     } 
     class Tree implements Serializable{} }