Thread: Runtime exception (Invalid Class exception) occurs. Please help

Hi
I am new to this forum and would appreciate any help that can be given. The following code is for an exercise in a book I am reading. It compiles fine but produces the following exception when executed.


java.io.InvalidClassException: Loan; local class incompatible: stream classdesc
serialVersionUID = -5273567861794013902, local class serialVersionUID = 19442595
53328340694
at java.io.ObjectStreamClass.initNonProxy(Unknown Source)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unkno wn Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at Exercise19_7.main(Exercise19_7.java:14)



Thanks in advance for any help.


Here is the code.

import java.io.*;
import java.util.*;
 
public class Exercise19_7 {
 
  public static void main(String[] args) throws ClassNotFoundException {
    	ArrayList<Loan> loanList = new ArrayList<Loan>();
	try{
          ObjectInputStream input = new ObjectInputStream(new FileInputStream("Exercise19_6.dat"));
	  while(true){
	    Loan loan = (Loan)(input.readObject());
	    loanList.add(loan);
	  }
	}
	catch (EOFException ex) {
		for(int i = 0; i < loanList.size(); i++){
		  System.out.println("Loan Date: " + ((Loan)(loanList.get(i))).getLoanDate());
		  System.out.println("Loan Amount: " + ((Loan)(loanList.get(i))).getLoanAmount());
		  System.out.println("Interest Rate: " + ((Loan)(loanList.get(i))).getAnnualInterestRate());
		  System.out.println("Number of years: " + ((Loan)(loanList.get(i))).getNumberOfYears());
		  System.out.println("Total Payment: " + ((Loan)(loanList.get(i))).getTotalPayment());
		}
        }
 
	catch (IOException ex) {
	  ex.printStackTrace();
	}
 
  }
 
}

Here is the Loan class. It has worked fine in other exercises.

import java.util.Date;
import java.io.*;
public class Loan implements Serializable {
 
  private double annualInterestRate;
  private int numberOfYears;
  private double loanAmount;
  private Date loanDate;
 
  public Loan() {
    this(2.5, 1, 1000);
 
  }
 
  public Loan(double annualInterestRate, int numberOfYears, 
      double loanAmount) throws IllegalArgumentException {
 
    if (annualInterestRate <= 0)
        throw new IllegalArgumentException("Interest rate must be more than zero");
    if (numberOfYears <= 0) 
        throw new IllegalArgumentException("Number of years must be more than zero");
    if (loanAmount <= 0)
        throw new IllegalArgumentException("Loan Amount must be more than zero");
    this.annualInterestRate = annualInterestRate;
    this.numberOfYears = numberOfYears;
    this.loanAmount = loanAmount;
    loanDate = new Date();
 
  }
 
  public Loan(Loan loan){
    this.annualInterestRate = loan.getAnnualInterestRate();
	this.numberOfYears = (int)(loan.getNumberOfYears());
	this.loanAmount = loan.getLoanAmount();
	this.loanDate = loan.getLoanDate();
 
 
  }
 
  public double getAnnualInterestRate() {
    return annualInterestRate;
 
  }
 
  public void setAnnualInterestRate(double annualInterestRate) throws IllegalArgumentException {
 
    if (annualInterestRate <= 0)
        throw new IllegalArgumentException("Interest rate must be more than zero");
 
    this.annualInterestRate = annualInterestRate;
 
  }
 
  public double getNumberOfYears() {
    return numberOfYears;
 
  }
 
  public void setNumberOfYears(int numberOfYears) throws IllegalArgumentException {
 
    if (numberOfYears <= 0) 
        throw new IllegalArgumentException("Number of years must be more than zero");
 
    this.numberOfYears = numberOfYears;
 
  }
 
  public double getLoanAmount() {
    return loanAmount;
 
  }
 
  public void setLoanAmount(double loanAmount) throws IllegalArgumentException {
 
    if (loanAmount <= 0)
        throw new IllegalArgumentException("Loan Amount must be more than zero");
 
    this.loanAmount = loanAmount;
 
  }
 
 
  public double getMonthlyPayment() {
    double monthlyInterestRate = annualInterestRate / 1200;
    double monthlyPayment = loanAmount * monthlyInterestRate / (1 -
      (Math.pow(1 / (1 + monthlyInterestRate), numberOfYears * 12)));
    return monthlyPayment;
 
  }
 
  public double getTotalPayment() {
    double totalPayment = getMonthlyPayment() * numberOfYears * 12;
    return totalPayment;
 
  }
 
 
  public Date getLoanDate() {
 
    return loanDate;
 
  }
 
}

InvalidClassException: Loan; local class incompatible: stream classdesc

c = -5273567861794013902,
local class serialVersionUID = 1944259553328340694

The text of the error message seems to say that the local class definition is not compatible with what is being read. Notice the serialVersionUIDs are different
What is the history of the class object and the serialized class? Are they from the same version of the class?

Add a serialVersionUID to the class so it doesn't generate a new one every time the code is compiled

Originally Posted by Norm

The text of the error message seems to say that the local class definition is not compatible with what is being read. Notice the serialVersionUIDs are different
What is the history of the class object and the serialized class? Are they from the same version of the class?

Add a serialVersionUID to the class so it doesn't generate a new one every time the code is compiled

Thanks for the reply. I am a newbie to Java so please forgive my ignorance. I created the Loan class several chapters ago and modified it for this exercise. It was not serialized prior to this so I added the "implements Serializable" code and a new Constructor to accept a Loan object as an argument. The chapter I am currently reading covers Binary I/O and introduces serialization.

How do I add a serialVersionUID to the class?

ok, I copied the stream serialVersionUID -5273567861794013902 and added it to a static final long variable in the Loan class and now the program is working. Thanks. I am new to serialization. Any thoughts as to why this happened? The book has not mentioned anything about serialVersionUID. I assume it is beyond the scope of an introductory textbook.

The serial ID is to allow the author of the program to tell the system when a new version of the class has been created that is NOT compatible with an older version. You would change it when you did not want someone to use an invalid, older version of a serialized class.

Originally Posted by Norm

The serial ID is to allow the author of the program to tell the system when a new version of the class has been created that is NOT compatible with an older version. You would change it when you did not want someone to use an invalid, older version of a serialized class.

Thanks again, Norm