Observer Interface and Observable Class

Q

How are Observer and Observable used?

✍: FYIcenter

A

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.

2007-03-03, 5809👍, 0💬

Importance of Synchronization
What is synchronization and why is it important? With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of... 2007-03-03, 7079👍, 0💬

Waiting State in a Thread
What are three ways in which a thread can enter the waiting state? A thread can enter the waiting state by invoking its sleep() method, by blocking on IO, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoki... 2007-03-03, 6585👍, 0💬

Synchronized Methods and Synchronized Statements
What are synchronized methods and synchronized statements? Synchronized methods are methods that are used to control access to a method or an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to s... 2007-03-03, 5999👍, 0💬

Acquiring Locks on Classes
Can a lock be acquired on a class? Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object. 2007-03-03, 5913👍, 0💬

Transient Variables
What is a transient variable? A transient variable is a variable that may not be serialized. If you do not want some variables to be serialized, you can mark those variables transient or static. 2007-03-03, 5880👍, 0💬

Externalizable Interface: readExternal() and readExternal()
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 readExternal(). 2007-03-03, 5850👍, 0💬

Serializable Interface
How many methods in the Serializable interface? There is no method in the Serializable interface. The Serializable interface acts as a marker, telling the object serialization tools that your class is serializable. 2007-03-03, 5842👍, 0💬

Observer Interface and Observable Class
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 obj... 2007-03-03, 5810👍, 0💬

Serializalble and Externalizable Interfaces
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 Extern... 2007-03-03, 5725👍, 0💬

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