Core Java perguntas e respostas de entrevista
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Pergunta 266. What's the use of concrete methods in abstract classes?
One of the design principles of Java inheritance is to create superclass methods that can be used by one or more subclasses, this avoids duplication of code and makes it easier to amend. The same principle holds with abstract classes that are fulfilled by numerous subclasses.
One useful technique with abstract classes is that a concrete method may be defined in anticipation of abstract methods being fulfilled in its subclasses. In the example below the AbstractShape class has a concrete printArea() method that calls the abstract getArea() method. Subclasses inherit the printArea() method and must implement the getArea() method to stand as concrete classes.
Pergunta 267. If an object is garbage collected, can it become reachable again?
Once an object is garbage collected, It can no longer become reachable again.
Pergunta 268. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup, before the object gets garbage collected. For example, closing an opened database Connection.
Pergunta 269. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.
Pergunta 270. an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object’s finalize() method may be invoked by other objects.
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Mais uteis segundo os usuarios:
- How could Java classes direct program messages to the system console, but error messages, say to a file?
- What are the differences between an interface and an abstract class?
- Why would you use a synchronized block vs. synchronized method?
- How can you force garbage collection?
- What are the differences between the methods sleep() and wait()?