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Ans. @Autowired and @Inject are similar in terms of functionality they achieve. @Inject is part of a new Java technology called CDI that defines a standard for dependency injection whereas @Autowired is a Spring specific annotation for dependency injection.
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Ans. Nagios is open source system , network and infrastructure monitoring software application. It alerts the user if anything goes wrong. Nagios is widely used as monitoring tool for enterprise applications.
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Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).
A class can extend single abstract class whereas it can implement multiple interfaces.
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Though the following code will compile fine but will result in ClassCastException during runtime.
Fruit fruit = new Apple();
Banana banana = Banana(fruit); // ClassCastException
This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception.
This exception can be avoided by following code.
Fruit fruit = new Apple();
if(fruit instanceOf Banana){
Banana banana = Banana(fruit); // ClassCastException
}
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Ans. Http is connection less by default. header informs hosts to keep the connection alive so that the same connection can be reused for multiple communication.
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Q777. Difference between HashMap and WeakHashMap ?
Ans. WeakHashMap uses weak reference for keys, which means if the key object doesn't have any reference then both key/value mapping will become eligible for garbage collection.
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Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.
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Which of the following can throw ClassCastException ?
