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Ans. Because of the life cycle requirement for different type of values in java.
variables initialized and used in functions needs to be destructed with the execution of function and hence kept in stack. Same is applicable for the object references initialized within the method. If objects would have been created in stack, they wouldnt have been passed around across methods and hence they are created on heap.
So anything that is required beyond the scope of a method or function is kept on heap which is usually garbage collected by Java.
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Ans. Inner Class is a class that is nested within another class whereas sub class is a class that extends or inherit another class.
Inner class can only be accessed using reference of outer class ( Class name , if inner class is static or object reference, if inner class is non static ) whereas Sub class is accessed directly.
In terms of memory, inner class is stored just like another class having it's own body whereas sub class carries the body of parent class as well as it's own fields in memory.
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Collection<Collection> collection = new LinkedList<Collection>();
is a valid initialization as collection being reference of "Collection" class can hold object of derived Class "LinkedList" due to runtime Polymorphism. Runtime polymorphism is not applicable to type arguments.
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Ans. List - Members are stored in sequence in memory and can be accessed through index.
Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates.
Map - Contains Key , Value pairs.
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Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.
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Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.
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Q126. What one should take care of, while serializing the object?
Ans. One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializable Exception.
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Ans. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to override the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language.
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Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation.
Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation.
Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types.
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote
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Ans. This Error is thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector.
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Sample Code for final variable
Which of following memory segment is cleaned by Garbage Collection Mechanism ?
