Java Interview Questions -Part 12

11. How many methods in the Externalizable interface?
There are two methods in the Externalizable interface. You have to implement these two methods in order to make your class externalizable. These two methods are readExternal() and writeExternal().
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12. What is the difference between Serializalble and Externalizable interface?
When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Externalizable interface, you have a complete control over your class's serialization process.
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13. What is a transient variable?
A transient variable is a variable that may not be serialized. If you don't want some field to be serialized, you can mark that field transient or static.
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14. Which containers use a border layout as their default layout?
The Window, Frame and Dialog classes use a border layout as their default layout.
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15. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
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