Core Java 面接の質問と回答
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質問 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.
質問 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.
質問 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.
質問 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.
質問 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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