为什么会抛出 IOException

Question

This program is run when there is no extant file named "Test Object.to". The output of this program is "IO caught". Why?

import java.io.*;

public class Test 
{
    public static void main (String [] args)
    {
        TestObject testObject = new TestObject("Test Object");
        
        try
        {
            saveTestObject(testObject);
        }
        catch (FileNotFoundException fnf)
        {
            System.out.println("FNF caught");
        }
        catch (IOException io)
        {
            System.out.println("IO caught");
        }
    }
    
    static void saveTestObject(TestObject to)  throws FileNotFoundException, IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(to.name + ".to"));
        oos.writeObject(to);
        oos.close();
    }
}

class TestObject
{
    String name;
    
    TestObject(String s)
    {
        name = s;
    }
}

Answer 1

First of all, this does not throw a FileNotFoundException , since as per the docs , FileOutputStream 's constructor will create the file if it doesn't exist instead of throwing an error. If you print the error, you see:

java.io.NotSerializableException: TestObject

Again, as per the docs , writeObject requires that its argument be Serializable . Since Serializable is just a marker interface, you can just implement it:

class TestObject implements Serializable

and now your code doesn't throw any errors.

Answer 2

好的，我现在看到 TestObject 显然需要实现 Serializable