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Is it sensible to use the hash code of a class as its serialVersionUID?


By : Siva Charan
Date : October 18 2020, 06:10 AM
To fix this issue Class has no explicitly defined hashCode() method, so it's not defined to be stable.
That means that you can (and probably will) get different results for MyClass.class.hashCode() between different runs, even on the same JVM and definitely between different JVM implementations and/or versions.
code :


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If I change the base class that a Java Exception class extends, do I need to update the serialVersionUID value?


By : user1452719
Date : March 29 2020, 07:55 AM
I hope this helps you . Given that the specification is unclear enough to cause confusion and debate, with no clear answer emerging, the only option left is to trust empirical evidence.
Taking the examples from the question above, of FooException deriving from BarException deriving from RuntimeException, and then removing BarException from the inheritance chain, I put together a sample application to try serialization and de-serialization in various combinations.

error: local class incompatible: stream classdec serialversionUID= ...., local class serialversionUID=


By : FruitChunks
Date : March 29 2020, 07:55 AM

Is serialVersionUID inherited by subclasses, if I have default serialVersionUID in superclass


By : Dean William
Date : March 29 2020, 07:55 AM
Does that help
Is serialVersionUID inherited by subclasses, if I have default serialVersionUID in superclass?

In a linked hash map <integer,class object>. how can I modify equals and hash code to display values?


By : user3681293
Date : March 29 2020, 07:55 AM
it helps some times equals(), hashCode() and dont forget compareTo() are used by many container classes to compare objects. The LinkedHashMap uses them to sort them properly into the map. Java does automatically generate them. You only need to overwrite them if the default does not work properly.
They are not meant to produce any output!
code :
public class Main
{

    public static class Person
    {
        String name;
        Integer age;

        public Person(String name, Integer age)
        {
            this.name = name;
            this.age = age;
        }

        @Override
        public String toString()
        {
            return "Person with name=" + name + " and age=" + age;
        }
    }

    public static void main(String[] args) throws Exception
    {
        LinkedHashMap<String, Person> map = new LinkedHashMap<String, Person>();

        // fill the map
        map.put("a", new Person("Stefan", 45));
        map.put("b", new Person("Lisa", 40));
        map.put("c", new Person("Madonna", 60));

        // print the map
        System.out.println(map);

        // or iterate over the content
        for (Map.Entry<String, Person> entry : map.entrySet())
        {
            System.out.println(entry.getKey() + "-->" + entry.getValue().toString());
        }
    }

}
{a=Person with name=Stefan and age=45, b=Person with name=Lisa and age=40, c=Person with name=Madonna and age=60}
a-->Person with name=Stefan and age=45
b-->Person with name=Lisa and age=40
c-->Person with name=Madonna and age=60

Why is method name considered or generating the hash for serialversionuid


By : Thibaud Marechal
Date : March 29 2020, 07:55 AM
should help you out The default is to make sure that your serialized objects are only compatible if they come from exactly the same class. For this, a number of attributes of the class are taken into account: https://docs.oracle.com/javase/6/docs/platform/serialization/spec/class.html#4100
In any case, if you use serialization, you should define your own id.
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