Why is a serializable inner class not serializable?

Question

The following code:

public class TestInnerClass {

    public static void main(String[] args) throws IOException {
        new TestInnerClass().serializeInne         


        

Answer 1

how about make TestInnerClass serializable?

public class TestInnerClass implements Serializable { }

Answer 2

InnerClass cannot be serialised because to instantiate it (as required during deserialization) you need a reference to an instance of the outer class

Instances of inner classes cannot exist without an instance of the outer class.

i.e

OuterClass o = new OuterClass();
OuterClass.InnerClass o_i = o.new InnerClass();

If you use static inner class, it will be possible to serialise the static inner class. The instances of static inner classes can be created standalone.

i.e

OuterClass o = new OuterClass();
OuterClass.InnerClass i = new OuterClass.InnerClass();

Answer 3

what if InnerClass needs this access?

Then it needs the outer class instance, and it must be serialized along with the inner class.

Is there a way to serialize a non-static inner class without the enclosing class, e.g. by making the reference to the outer class transient?

No. What would happen when you deserialize such a class and then try to call an instance method of the outer class? A NullPointerException?