little problem in 2 classes' serializaiton&deserialization

[sarrah gerard]

Hi everybody,
I am confused again, why it gives that java.lang.ClassCastException ? I have default constructors for Profile class and School class. What can be the problem? i think my brain become juicy!
Exception in thread "main" java.lang.ClassCastException: Profile cannot be cast to MyClassToBePersisted
at DeserializeMyClass.main(DeserializeMyClass.java:30)

now it is
Exception in thread "main" java.lang.NullPointerException
at DeserializeMyClass.main(DeserializeMyClass.java:43)
Java Result: 1

System.out.println("School: " + mySchool.toString());

What is wrong with this statement?
Java Result: 1

  
import java.io.Serializable;

public class Profile implements Serializable{
 public Profile(){

    }
    static void getProfile(String string, int i, String string0) {
        
    }
    
private String name;
        private int age;
        private String hobby;

     public Profile(String name, int age,String hobby){
         this.name = name;
         this.age = age;
         this.hobby=hobby;
     }

     public String getName(){
        return name;
    }

    public void setName(String name){
        this.name = name;
    }
    public int getAge(){
        return age;
    }
    public void setAge(int age){
        this.age=age;
    }
  public String getHobby(){
        return hobby;
    }

    public void setHobby(String hobby){
        this.hobby = hobby;
    }
     @Override
     public String toString(){
         StringBuffer myBuffer = new StringBuffer();
         myBuffer.append(this.name+" ,"+this.age+ "," +this.hobby);
         return myBuffer.toString();
     }

}

   
import java.io.Serializable;

public class School implements Serializable{
public School(){

     }
    static void getSchool(String string, int i) {
       
    }

     private String nameOfSchool;
     transient private int yearStarted;

    public String getNameOfSchool() {
        return nameOfSchool;
    }

    public int getYearStarted() {
        return yearStarted;
    }

    public void setNameOfSchool(String nameOfSchool){

    }
    public void setYearStarted(int yearStarted){
        
    }
    @Override
     public String toString(){
         StringBuffer myBuffer = new StringBuffer();
         myBuffer.append(this.nameOfSchool+" ,"+this.yearStarted);
         return myBuffer.toString();
     }

}

  import java.io.Serializable;
import java.util.Date;

public class MyClassToBePersisted implements Serializable{

 static final long serialVersionUID = -3126998878902358585L;

    private Date time;
    private School school;
    private Profile profile;

    public MyClassToBePersisted(School school, Profile profile) {

    }

    MyClassToBePersisted() {
        
    }

    public School getSchool(){
         return school;
     }

    public void setProfile(Profile profile) {
        
    }

    public void setSchool(School school) {
      
    }

    public Profile getProfile(){
         return profile;
     }

    public Date getTime() {
        return time;
    }
}  

   import java.io.ObjectOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class SerializeMyClass  {
 public static void main(String [] args){

  String filename = "MyClassToBePersisted.ser";
         if(args.length > 0) {
             filename = args[0];
         }

         Profile MyClassToBePersisted =new Profile();

          School.getSchool("harvard", 22);
         Profile.getProfile("mary", 11, "paint");


         // Serialize the object instance and save it in
         // a file.
         FileOutputStream fos = null;
         ObjectOutputStream out = null;
         try {
             fos = new FileOutputStream(filename);
             out = new ObjectOutputStream(fos);
             out.writeObject(MyClassToBePersisted);
             out.close();
         } catch(IOException ex) {
             ex.printStackTrace();
         }

         System.out.println("Current time is saved into " + filename);
     }
}
 

   import java.io.ObjectInputStream;
import java.io.FileInputStream;
import java.io.IOException;

public class DeserializeMyClass {

public static void main(String [] args) {

        String filename = "MyClassToBePersisted.ser";
        if(args.length > 0) {
            filename = args[0];
        }

        
        MyClassToBePersisted myPers = null;
        FileInputStream fis = null;
        ObjectInputStream in = null;
        try {
            fis = new FileInputStream(filename);
            in = new ObjectInputStream(fis);
            myPers = (MyClassToBePersisted)in.readObject();
            in.close();
        } catch(IOException ex) {
            ex.printStackTrace();
        } catch(ClassNotFoundException ex) {
            ex.printStackTrace();
        }

        // print out restored time
        School mySchool = myPers.getSchool();
        Profile myProfile = myPers.getProfile();

        System.out.println("School: " + mySchool.toString());
        System.out.println("Profile: " + myProfile.toString());

    }
} 

[sarrah gerard]

now it is
Exception in thread "main" java.lang.NullPointerException
at DeserializeMyClass.main(DeserializeMyClass.java:43)
Java Result: 1

System.out.println("School: " + mySchool.toString());

What is wrong with this statement?

[Ulf Dittmer]

For starters, the Profile.getProfile and School.getSchool methods do nothing. And the MyClassToBePersisted.setProfile and MyClassToBePersisted.setSchool methods do nothing either, and they're not even called by the SerializeMyClass class (which I think should happen, if I guess correctly what the code should do). So the answer to the question of why there's a NullPointerException is: Because "mySchool" is null, and the reason it's null is because the object that gets persisted never has a School (or a Profile) object set.

[sarrah gerard]

Ulf Dittmer wrote:For starters, the Profile.getProfile and School.getSchool methods do nothing. And the MyClassToBePersisted.setProfile and MyClassToBePersisted.setSchool methods do nothing either, and they're not even called by the SerializeMyClass class (which I think should happen, if I guess correctly what the code should do). So the answer to the question of why there's a NullPointerException is: Because "mySchool" is null, and the reason it's null is because the object that gets persisted never has a School (or a Profile) object set.

Thank you Ulf.
But ,I understand like this;

I add to Profile class

     public static Profile getProfile(String name, int age, String hobby){
         return new Profile(name, age,hobby);
     }

I add to School class

   ]public static School getSchool(String nameOfSchool, int year){
         return new School(nameOfSchool, year);
     }

Then,I erased the set methods in MyClassToBePersisted.java

Now, when ı run , the output is:
<run:
null
null


ı had these

 School.getSchool("harvard", 2000);
         Profile.getProfile("mary", 11, "paint");

in SerializeMyClass.
Why it gives null null?

[Ulf Dittmer]

You need the setter methods that you deleted. Think about this: What happens to the objects that are returned by School.getSchool and Profile.getProfile? Do they end up where you expect them to end up?

[sarrah gerard]

Ulf Dittmer wrote:You need the setter methods that you deleted. Think about this: What happens to the objects that are returned by School.getSchool and Profile.getProfile? Do they end up where you expect them to end up?

ı add the set methods, but the conclusion doesn't change. I just want to see the values of School.getSchool("...",..); and Profile.getProfile("mary", 11, "paint") when ı run DeserializeMyClass.java
but , it gives null null

[Ulf Dittmer]

How are you using the setter methods? If the school and profile fields of the MyClassToBePersisted object are null before you even serialize (and I suspect they are), then something is still missing.

[sarrah gerard]

Ulf Dittmer wrote:How are you using the setter methods? If the school and profile fields of the MyClassToBePersisted object are null before you even serialize (and I suspect they are), then something is still missing.

  import java.io.Serializable;
import java.util.Calendar;
import java.util.Date;
/**
 *
 * @author ppty
 */
public class MyClassToBePersisted implements Serializable{
 
 static final long serialVersionUID = -3126998878902358585L;

    private Date time;
    private School school;
    private Profile profile;


public MyClassToBePersisted(){
    time =Calendar.getInstance().getTime();
}
    public MyClassToBePersisted(School school, Profile profile) {
        this.school=school;
        this.profile=profile;
    }


    public School getSchool(){
         return school;
     }

    public void setProfile(Profile profile) {
        this.profile=profile;
    }

    public void setSchool(School school) {
      this.school=school;
    }

    public Profile getProfile(){
         return profile;
     }

    public Date getTime() {
        return time;
    }


}

When i serialize, output is:
run:
Current is saved into MyClassToBePersist.ser
BUILD SUCCESSFUL (total time: 0 seconds)

When i deserialize, output is:
null
null

you defines well but i'm veery beginner.and not understand your opinions clearly sorry
What can i do now?

[Ulf Dittmer]

You only showed how you defined the setter methods, not how you're using them; in particular, which arguments are you passing to them?

And again:

If the school and profile fields of the MyClassToBePersisted object are null before you even serialize (and I suspect they are), then something is still missing.

[sarrah gerard]

Ulf Dittmer wrote:You only showed how you defined the setter methods, not how you're using them; in particular, which arguments are you passing to them?

And again:

If the school and profile fields of the MyClassToBePersisted object are null before you even serialize (and I suspect they are), then something is still missing.

in SerializeMyClass.java

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

          School.getSchool("harvard", 2000);
         Profile.getProfile("mary", 11, "paint"); 

  import java.io.Serializable;

public class Profile implements Serializable{
 public Profile(){

    }
    
    
private String name;
        private int age;
        private String hobby;

     public Profile(String name, int age,String hobby){
         this.name = name;
         this.age = age;
         this.hobby=hobby;
     }
         public static Profile getProfile(String name, int age, String hobby){
         return new Profile(name, age,hobby);
     }
     public String getName(){
        return name;
    }

    public void setName(String name){
        this.name = name;
    }
    public int getAge(){
        return age;
    }
    public void setAge(int age){
        this.age=age;
    }
  public String getHobby(){
        return hobby;
    }

    public void setHobby(String hobby){
        this.hobby = hobby;
    }
     @Override
     public String toString(){
         StringBuffer myBuffer = new StringBuffer();
         myBuffer.append(this.name+" ,"+this.age+ "," +this.hobby);
         return myBuffer.toString();
     }

}  

  import java.io.Serializable;
class School implements Serializable{

    public static School getSchool(String nameOfSchool, int yearStarted){
         return new School(nameOfSchool, yearStarted);
    }
public School(){

     }
     private String nameOfSchool;
     transient private int yearStarted;
     public School(String nameOfSchool, int yearStarted){
         this.nameOfSchool = nameOfSchool;
         this.yearStarted = yearStarted;
         
     }

    public String getnameOfSchool() {
        return nameOfSchool;
    }

    public int getYearStarted() {
        return yearStarted;
    }

    public void setnameOfSchool(String nameOfSchool){
    this.nameOfSchool=nameOfSchool;
    
    }
        

    public void setYearStarted(int yearStarted){
        this.yearStarted = yearStarted;
    }
    @Override
     public String toString(){
         StringBuffer myBuffer = new StringBuffer();
         myBuffer.append(this.nameOfSchool+" ,"+this.yearStarted);
         return myBuffer.toString();
     }

}  

[Ulf Dittmer]

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

          School.getSchool("harvard", 2000);
         Profile.getProfile("mary", 11, "paint"); 

This is the key section. You're not using the objects returned by the getSchool/getProfile methods - you're throwing them away. You need to pass those to the MyClassToBePersist.setSchool and setProfile method calls.

By the way, you should get in the habit of giving your variables names that start with lowercase letters (like "myClassToBePersist") - it's what every Java programmer in this world expects. You'll confuse people if you use names that start with uppercase letters - those are used for classes.

[sarrah gerard]

Ulf Dittmer wrote:

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

          School.getSchool("harvard", 2000);
         Profile.getProfile("mary", 11, "paint"); 

This is the key section. You're not using the objects returned by the getSchool/getProfile methods - you're throwing them away. You need to pass those to the MyClassToBePersist.setSchool and setProfile method calls.

By the way, you should get in the habit of giving your variables names that start with lowercase letters (like "myClassToBePersist") - it's what every Java programmer in this world expects. You'll confuse people if you use names that start with uppercase letters - those are used for classes.
Do you mean like that?
MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

MyClassToBePersist.getProfile().setName("mary");
MyClassToBePersist.getProfile().setAge(11);
MyClassToBePersist.getProfile().setHobby("paint");


MyClassToBePersist.getSchool().setnameOfSchool("harvard");
MyClassToBePersist.getSchool().setYearStarted(2000);
this gives same NullPointerException , my fault

[Ulf Dittmer]

No, that's not what I meant. In your very first post you had these methods in your MyClassToBePersisted class:

   public void setProfile(Profile profile) {  
     
     }    
     public void setSchool(School school) {  
         
     }  

You need to call those methods on your myClassToBePersist object, and you need to pass along the objects you get from the getSchool/getProfile methods. And, obviously, those setter methods need to do something - they need to store the objects you pass into them.

[sarrah gerard]

Ulf Dittmer wrote:No, that's not what I meant. In your very first post you had these methods in your MyClassToBePersisted class:

   public void setProfile(Profile profile) {  
     
     }    
     public void setSchool(School school) {  
         
     }  

You need to call those methods on your myClassToBePersist object, and you need to pass along the objects you get from the getSchool/getProfile methods. And, obviously, those setter methods need to do something - they need to store the objects you pass into them.

Yes, i have set methods in MyClassToBePersisted class
And i changed sth. like that :

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

         MyClassToBePersist.getProfile().setProfile("mary",11,"paint");

         MyClassToBePersist.getSchool().setSchool("harvard",2000);  

[Ulf Dittmer]

You're getting closer, but you're still not calling the setSchool and setProfile methods of the MyClassToBePersisted class. You're calling the setProfile/setSchool methods of the Profile and School classes. Remember that the setSchool/setProfile methods of the MyClassToBePersisted class take a School/Profile object as parameter, not the individual values. Your code should look like this:

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

         MyClassToBePersist.setProfile(A SINGLE PARAMETER GOES HERE);

         MyClassToBePersist.setSchool(ANOTHER SINGLE PARAMETER GOES HERE);  

[sarrah gerard]

Ulf Dittmer wrote:You're getting closer, but you're still not calling the setSchool and setProfile methods of the MyClassToBePersisted class. You're calling the setProfile/setSchool methods of the Profile and School classes. Remember that the setSchool/setProfile methods of the MyClassToBePersisted class take a School/Profile object as parameter, not the individual values. Your code should look like this:

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

         MyClassToBePersist.setProfile(A SINGLE PARAMETER GOES HERE);

         MyClassToBePersist.setSchool(ANOTHER SINGLE PARAMETER GOES HERE);  

is it in SerializeMyClass class? If so, it gives error. Did you mean profile or school with "single parameters" ?

   MyClassToBePersisted MyClassToBePersist=new MyClassToBePersisted();

         MyClassToBePersist.setProfile(profile);
         MyClassToBePersist.setSchool(school); 

[sarrah gerard]

Ok i got it, now it runs
Your explanation help me, thanks Ulf,have a nice day