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Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level
2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.
3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.
4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.
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Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -
1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.
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Ans. There can be two different elements with the same hashcode. When two elements have the same hashcode then Java uses the equals to further differentation. So there can be one or two objects depending on the content of the objects.
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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
Q6. What is the difference between StringBuffer and String class ?
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.
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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. A has dependency of B, B has dependency of C and C has dependency of A
With Maven 2 , came transitive dependency wherein in above scenario, C will acts as a dependency of A as if this dependency has been defined directly in A but the negative side is that if it leads to cyclic dependency , it creates problems.
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Ans. The problem with serialized singleton class is that whenever we deserialize it, it will create a new instance of the class. To overcome this scenario all we need to do is to provide the implementation of readResolve() method.
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Ans. Class loaders are hierarchical. The very first class is specially loaded with the help of static main() method declared in your class. All the subsequently loaded classes are loaded by the classes, which are already loaded and running.
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Q17. There are 8 balls, 7 weigh 100 gms, 1 is defective, there is a weighing scale, any number of balls can be measured at the same time. in how many attempts defective balls can be found out.
Ans. Work with two pointers on the linked list - a slow pointer (increments by one node) and a fast pointer (increments by two nodes). If both of these pointers meet at the same node, then there is a cycle in the linked list. Otherwise, no cycle.
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Ans. Creating an index creates a separate table. ... Indexes are used to speed the search of data within tables. Partitions provide segregation of the data at the hdfs level, creating sub-directories for each partition. Partitioning allows the number of files read and amount of data searched in a query to be limited
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Ans. ConcurrentHashMaps provide unlimited read operation fro multi threaded environment. For write operation only one thread can change value for particular segment of map.
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Ans. Every fresh session having its own cache memory, Caching is a mechanism for storing the loaded objects into cache memory. The advantage of cache mechanism is, whenever again we want to load the same object from the database then instead of hitting the database once again, it loads from the local cache memory only, so that the no. of round trips between an application and a database server got decreased. It means caching mechanism increases the performance of the application.
In hibernate we have two levels of caching
First Level Cache [ or ] Session Cache
Second Level Cache [ or ] Session Factory Cache [ or ] JVM Level Cache
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