Latest java, spring, hibernate, web services

Latest Java(spring hibernate,web services,SQL etc) interview Questions: 

• Explain about Optimistic and pessimistic lock in hibernate
As per hibernate guidance two locks are defined as below
Optimistic:
Optimistic locking that multiple transactions can complete without affecting each other, and that therefore transactions can proceed without locking the data resources that they affect. Before committing, each transaction verifies that no other transaction has modified its data. If the check reveals conflicting modifications, the committing transaction rolls back[1].
Pessimistic:
Pessimistic locking assumes that concurrent transactions will conflict with each other, and requires resources to be locked after they are read and only unlocked after the application has finished using the data.
• Get & load difference in hibernate

Load and get, both methods are calling from session Object in hibernate.
when calling the load() method it took the data that already loaded and stored in session. if data not available in session then only it hits the database.
In case of get() method, irrespective of availability in session it hits the database and get the requested data.

• Transaction management in hibernate
Transaction described by properties, we called as ACID properties,
Atomacity: In a transaction involving two or more discrete pieces of information, either all of the pieces are committed or none are.
Consistency: A transaction either creates a new and valid state of data, or, if any failure occurs, returns all data to its state before the transaction was started.
Isolation: A transaction in process and not yet committed must remain isolated from any other transaction.
Durability: Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state.
• Spring 3 vs Spring 4
spring 3 supports Java 5.x version features such as Java-based @Configuration model
Spring4 is first to fully support Java 8 features. You can still use Spring with older versions of Java, however, the minimum requirement has now been raised to Java SE 6.All deprecated packages, and many deprecated classes and methods have been removed with version 4.0
Note that optional third-party dependencies have been raised to a 2010/2011 minimum (i.e. Spring 4 generally only supports versions released in late 2010 or later now): notably, Hibernate 3.6+, EhCache 2.1+, Quartz 1.8+, Groovy 1.8+, and Joda-Time 2.0+. As an exception to the rule, Spring 4 requires the recent Hibernate Validator 4.3+, and support for Jackson has been focused on 2.0+ now (with Jackson 1.8/1.9 support retained for the time being where Spring 3.2 had it; now just in deprecated form).
• Scopes in spring
Five types of scopes supported by spring bean :
singleton – Return a single bean instance per Spring IoC container
prototype – Return a new bean instance each time when requested
request – Return a single bean instance per HTTP request.
session – Return a single bean instance per HTTP session.
globalSession – Return a single bean instance per global HTTP session.
• In mutilthread environment, which scope you will use
Singleton scope has to use in mutilthread environment as a mutiple threads accessing the same object so that we can avoid the data multiple threads accesing the same object through synchronization concept.
• Spring integration
Thanks for your interest, we will post the Answer soon...
• Checked and unchecked exception
checked exception can be identifiable in compile time so that it called as compile time errors. IOException is one of the example for Checked Exception.
unchecked exception also called runtime errors, we can avoid or handle these by using try catch block.RuntimeException and it sub-classes are example for unchecked exceptions. We can't rectify the exception but we can escape from the exception by declaring the throws or try catch block in the code.
• Collection types
two types of collection classes availble in collection package...
single dimention arrayand double dimention array.
List and set are single dimention arrays, map is double dimention array.
Collection intreface is super class for the both List and set. List is the type of maintaaning the duplicate object with index. that means whatever order you are inserted and getting the same order.
• Java5 features
Generics, Enhanced for Loop, Autoboxing/Unboxing, Typesafe Enums, Varargs, Static Import, Metadata (Annotations)
• Generics and auto boxing
System allows a type or method to operate on objects of various types while providing compile-time type safety. It adds compile-time type safety to the Collections Framework and eliminates the difficulty in casting
automate the typec asting between primitve types to wrapper classes is overview of the Auto boxing. or in other words from Orcle, This facility eliminates the drudgery of manual conversion between primitive types (such as int) and wrapper types (such as Integer).
• Difference between set and map

Set	Map
1)set is single dimention arrays that hold the group of objects. 2)Duplicates obects are not allowed 3) if duplicate object inserted the it will override the existing object 4)Set doesn't maintan the order or index. if order requires without duplicates, LinkedHashSet is best option which is sub-class of Set.	1)Map is double dimetion array which hold the objects as key valew pair 2)Map can hold the duplicate objects but not duplcate keys. 3)order is not preserved.

• How hashmap will work
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• Comparator how it works
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• Unit testing how will you do in your project
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• How will you give security for web services
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• Car parking algorithm
• Hash collision
• Arraylist with concurreny modification exception
• Substring and intern method memory leakages
• Spring scopes 
• Variable with instance and variable without instance which one you will use Singleton and prototype scopes
• Any other implemantions for DI / IOC
• Do i need to close result set in jdbc
• If two class loaders wants to use one singletion objects how many instances will use ( one or two )
• Singleton design pattern
• Can we create Singleton in static nested class
• Immutable classes how can write
• Which one you will prefer mutable or immutable object as key in hashmap
• Can we write own dialect in hibernate
• When we will go for immutable class
• For password which one you will use string or char ? Why ?
• Oops principles like solid principle**
• how many minimum tables required for many-to-many mapping in hibernate
• Different way to implement synchronization
• out of memory issue
• Spring annotation: @ transactional
• memory handle in java ( stack & heap)
• What is the alternate for array list for synchronization
• Cache concept in hibernate ( second level cache Ehcache configuration)
• transaction management in Spring, how it will work
• Java 8 features

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