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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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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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Ans. Iterators in java are used to iterate over the Collection objects.
Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.
Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.
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Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.
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Ans. A finally block of code always executes, whether or not an exception has occurred.The only time finally won't be called is if you call System.exit() or if the JVM crashes first.
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Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.
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Q9. What is rule regarding overriding equals and hashCode method ?
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In Case a method is declared to throw an exception , We can only use a call to that method if ...
