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Q1081. Why Collection interface does not extend Cloneable interface ?

Ans. Here is the list of classes that implements Collections Interface - http://www.buggybread.com/2015/02/java-collections-classes-that-implement.html

Having Collection interface to extend Cloneable interface would mean necessarily implement clone method by all implementing classes. As not all collection classes allow duplicate elements, it makes no sense to clone elements for them.

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Q1082. What happens to the Exception object after the exception handling is done ?

Ans. As with all other objects its garbage collected after its usage unless its rethrown.

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Q1083. What are the disadvantages of multithreading ?

Ans. 1. Switching Overheads - Even though multi threading aims at improving performance by reducing the wait time and hence improving overall throughput, there is a cost of switching resources between threads and sometime this cost can surpass the benefits if there isnt much wait for IO or external communication.

2. Debugging is hard with multi threaded code.

3. Deadlock - Execution of multi threaded code many a times lead to deadlock due to shared resources.

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Q1084. What is the difference between Controller and Task Command ?

Ans. Controller Command is the command that gets called upon a request, just like We have actions in struts and controller in Spring. Task is a step in this bigger process. Task command are the commands that perform specific task for a controller command, like service classes in other frameworks. In order to complete the request, a controller command may invoke multiple task commands.

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Q1085. Which is the root interface of Collection classes in Java ?

Ans. java.util.Collection

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Q1086. Write code for Binary tree traversal ?

Ans. http://javabeat.net/binary-search-tree-traversal-java/

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Q1087. Explain what happens when insertion is performed in case of ArrayList and LinkedList.

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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Q1088. How to Bulk upload the data into Oracle database?

Ans. We can use external table feature of Oracle.

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Q1089. Can there be a Thread without a Process ?

Ans. No.

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Q1090. Can we have an inner class within Interface ?

Ans. Yes, we can define an inner class within interface.Inside the interface, the inner class is implicitly public static.

So the following is legit in Java

public interface BuggyBreadInterface {
   void doSomething();

   public class BuggyBreadClass implements BuggyBreadInterface{
      void doSomething(){
         System.out.println("Do something");
      }
   }
}

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Q1091. Is it a valid identifier in Java ?

int 123Abc = 5;

Ans. No, identifier in java cannot start with a numeral.

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Q1092. What is the difference between Collections.emptyList() and creating new instance of List using new ?

Ans. But Collections.emptyList() returns an Immutable list whereas new arraylist() creates a mutable list.

Advantage of getting an empty list using Collections.emptyList is that it returns a singleton list which can be shared among many references and hence made immutable. This is good fit for situations where we would like to initialize a list to basic minimum empty to avoid null pointer exception.

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Frequently asked Design Pattern interview question.

Q1093. What is a prototype design pattern ?

Ans. The prototype pattern is a creational design pattern. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. Prototype is used when we need duplicate copies of objects.

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Q1094. Write a Test Case using Mock ?

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=mock&category=code

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Very frequently asked.

Q1095. What is the use of synchronized keyword ?

Ans. Synchronize is used to achieve mutual exclusion i.e at one time, the segment of the code, method that has been declared synchronized should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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Q1096. Write an SQL Statement to add a foreign key constraint in oracle ?

Ans. ALTER TABLE <Table_Name> ADD CONSTRAINT <Constraint_Name> FOREIGN KEY (<Column_Name>) REFERENCES <Foreign_Table>(<Foreign_Column>);

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Q1097. How to Change Default Boot Kernel in Linux ?

Ans. https://www.redhat.com/archives/rhl-list/2005-April/msg04167.html

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Q1098. What is a Test Dependency Scope in Maven ?

Ans. This scope indicates that the dependency is not required for normal use of the application, and is only available for the test compilation and execution phases. This scope is not transitive.

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Q1099. What does the web status code 404,500 and 200 mean ?

Ans. 404 means the resource is not found on the server.The resource might not be deployed correctly.

500 means internal server error which means that resource was located but then it resulted in some exception or error.

200 means Ok.

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Try 1 Question(s) Test

Q1100. If Project A is calling web service of project B and there are some changes in project B, Will Project A needs to be rebuilt ?

Ans. That depends if the interface for the resource in Project B gets changed. If only the internal implementation is changed, No change is required in Project A. Project A is not even required to be rebuilt.

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Q1101. What is Dirty read in Database Transactions ?

Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.

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Q1102. What is difference between Product and Item ?

Ans. Item is a sale-able merchandise where as Product is a group of sale-able merchandise which share certain attributes. For example - Cell phone is a product whereas Samsung Galaxy S2 - White is an item.

Quantity is always attached to SKU ( Stock keeping unit ) or items. Product quantity has no relevance in terms of identify the current stock or reorder condition.

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Q1103. Have you ever felt the need of keeping the constructor private ?

Ans. Yes, When either we don't want an object to be created ( class having all static elements and hence not required ) or object to be created using a static method or static block. One such example could be a situation when we would like app to load objects at start up and we would like to restrict new object creation by any request.

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Usually asked with Questions related to Generics.

Q1104. What are Type Erasures in Java ?

Ans. Type erasure applies to the use of generics. When generics are used, they're pre compiled into compile time checks and execution-time casts.

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Q1105. Have you ever tried compressing data using Java ?

Ans. Yes, we can use ZipInputStream class for compressing the FileInputstream object.

Sample Code for ZipInputStream

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Q1106. Watching a directory for changes. Monitoring a directory.

Ans. http://www.logicbig.com/tutorials/core-java-tutorial/java-nio/java-watch-service/

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Q1107. How can one determine if JVM is 32-bit or 64-bit from Java Program ?

Ans. There is a Java system property "sun.arch.data.model" that can tell if JVM is 32 bit of 64 bit

System.getProperty("sun.arch.data.model") can be used to get that property.

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Q1108. Is ++ or -- operation thread safe in Java ?

Ans. No

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Q1109. How can we find the memory usage of JVM from Java code?

Ans. Using Runtime object.

Runtime runtime = Runtime.getRuntime();

runtime.totalMemory();
runtime.freeMemory();

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Q1110. How can we catch an exception thrown by another thread ?

Ans. http://stackoverflow.com/a/6548203/2789764

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