How are Observer and Observable used?

Q

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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.

2012-05-31, 2964👍, 0💬

How are Observer and Observable used?
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... 2012-05-31, 2965👍, 0💬

How many methods in the Externalizable interface?
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(). 2012-05-29, 2965👍, 0💬

What is the difference between Serializalble and Externalizable interface?
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... 2012-05-29, 2919👍, 0💬

What is a transient variable?
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. 2012-05-30, 2912👍, 0💬

How many methods in the 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. 2012-05-28, 2908👍, 0💬

What are 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... 2012-06-04, 2891👍, 0💬

What's new with the stop(), suspend() and resume() methods in JDK 1.2?
What's new with the stop(), suspend() and resume() methods in JDK 1.2? The stop(), suspend() and resume() methods have been deprecated in JDK 1.2. 2012-06-05, 2844👍, 0💬

What are three ways in which a thread can enter the waiting state?
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... 2012-06-04, 2817👍, 0💬

What is synchronization and why is it important?
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... 2012-05-31, 2759👍, 0💬

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