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Ans. Classes having only static methods in java is called util classes. As they don't have specific object state, they are basically intend to have shared code and state through static elements and methods. They save resources by sharing code.
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Ans. Though it's useful but it's not as useful as overriding member or object methods. We cannot achieve polymorphic behavior with static methods by overriding their definition in derived class.
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Ans. I like to keep the names in Capital Camel case. Moreover I prefer to keep the names for classes, enums and interfaces such that they are easily distinguishable just by the pattern of their names.
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This question is usually asked to check if you gel good with people of different background and are no racist at work. Be very cautious about answering such questions as any negative answer may lead to immediate rejection in spite of an excellent technical rounds.
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Null value means that the value is yet to be assigned or need not be assigned whereas empty value means that the blank value has already been assigned once. Null is the default for the null able columns that hasn't be assigned any value.
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Ans. We can declare the reference as final to avoid reassignment but again we can always initialize the final reference to null. Even if there was any such facility available , it would have meant poor use of resources by assigning a new object in memory to each reference that's created. Many a times references are just meant to refer to other objects which already have a reference i.e sharing object by multiple references.
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Ans. Application is unable to insert a record as it violates a unique constraint.
The exception states the constraint and Table can be located by the Entity mapping. So I will go to the DB and will first check to which all columns the unique constraint applies. And then I will go and check the code and logs to see how come the duplicate column values were attempted to be inserted when they were not supposed to be.
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Ans. Unique constraint ensures that a columns or combination or columns are always unique in a table and hence doesn't allow null or duplicates to be entered for the column or combination of columns.
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Ans. Primary Key constraint means that the column(s) should be unique and doesn't allow null. So Primary key constraint implies unique and not null constraint too.
Unique constraint implies not null constraint too as allowing null would violate uniqueness on those columns.
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Ans. A gobbler class take care of reading from a stream and optionally write out to another stream. Allows for non blocking reads when invoking a process through Runtime.exec(). Moreover the user can specify a callback that is called whenever anything is read from the stream.
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