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 Q841. If we parse any string to get another data type and the String doesn't abide by the type of data it should have hold, what would happen ?Core Java
Ans. It will throw Parse Exception.

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 Q842. Why calculations in float or Double sometimes gives unpredictable results ?Core Java
Ans. Because the way float values are stored its not precise.

For example - 0.1 is actually stored as
0.1000000000000000055511151231257827021181583404541015625

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 Q843. how can we get the System Environment variables from within Java program ? Core Java
Ans. We can use System.getenv for getting the environment variables. For ex - System.getenv("JAVA_HOME")

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 Q844. How to check the version of Java through Java program itself ?Core Java
Ans. We can use System.getProperty("java.version");

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 Q845. How can you check if a String is a 10 digit number by using regular expression ?Core Java
Ans. We can use \d{10} as the expression to check that

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 Q846. How can we catch an exception thrown by another thread ?Core Java
Ans. http://stackoverflow.com/a/6548203/2789764

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 Q847. How can we find the memory usage of JVM from Java code?Core Java
Ans. Using Runtime object.

Runtime runtime = Runtime.getRuntime();

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

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 Q848. Is ++ or -- operation thread safe in Java ?Core Java
Ans. No

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 Q849. How can one determine if JVM is 32-bit or 64-bit from Java Program ?Core Java
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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   Like         Discuss         Correct / Improve     jvm      intermediate        rare

 Q850. Watching a directory for changes. Monitoring a directory.Core Java
Ans. http://www.logicbig.com/tutorials/core-java-tutorial/java-nio/java-watch-service/

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 Q851. Have you ever tried compressing data using Java ?Core Java
Ans. Yes, we can use ZipInputStream class for compressing the FileInputstream object.

  Sample Code for ZipInputStream

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Usually asked with Questions related to Generics.
 Q852. What are Type Erasures in Java ?Core 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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   Like         Discuss         Correct / Improve     type erasures  generics     Asked in 2 Companies      intermediate        rare

 Q853. How do you prefer to store money values in your application ?Core Java
Ans. At Application level we use either Double or BigDecimal , preferably BigDecimal. At Database level we use Number with decimal precision 3.

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Basic and Very Frequently asked.
  Q854. What is Polymorphism in Java ?Core Java
Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

  Sample Code for overloading

  Sample Code for overriding

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Very frequently asked.
 Q855. What is the use of synchronized keyword ?Core Java
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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Frequently asked.
 Q856. When does the finally block gets executed ?Core Java
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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   Like         Discuss         Correct / Improve     finally  exception handling  exceptions     Asked in 4 Companies      basic        frequent

 Q857. What is the difference between Collections.emptyList() and creating new instance of List using new ?Core Java
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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   Like         Discuss         Correct / Improve     collections  Collections.emptyList  immutable  immutability  immutability

 Q858. Is it a valid identifier in Java ?

int 123Abc = 5;		Core Java
Ans. No, identifier in java cannot start with a numeral.

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 Q859. Can we have an inner class within Interface ?Core Java
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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 Q860. Write code for Binary tree traversal ?Core Java
Ans. http://javabeat.net/binary-search-tree-traversal-java/

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 Q861. Can you assign value to a static final type at runtime ?Core Java
Ans. No

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   Like         Discuss         Correct / Improve     static  final  static final     Asked in 1 Companies

 Q862. In case of a synchronized method, Does the method only gets locked or the whole object ?Core Java
Ans. Just the method gets locked.

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   Like         Discuss         Correct / Improve     synchronization  multithreading     Asked in 1 Companies

Very Frequently asked to fresh graduates and less experienced.
 Q863. What are the principle concepts of Object Oriented Programming ?Core Java
Ans. Abstraction Polymorphism Inheritance Encapsulation

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 Q864. Can we have try statement without catch? If try statement contains return will the finally block be executed? What happens if there is an exception inside finally block?Core Java
Ans. Yes, with finally.

Yes, finally block will be executed even if there is no exception in try block.

If finally throws an exception, the exception gets thrown to the calling module.

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   Like         Discuss         Correct / Improve     exception handling     Asked in 1 Companies      intermediate

 Q865. Explain Exception Hierarchy in Java SE ?Core Java
Ans. <a href="http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/" rel="nofollow">http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/</a>

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   Like         Discuss         Correct / Improve     exception hierarchy   exceptions     Asked in 3 Companies

 Q866. Which data structure would you recommend for ordered and sorted data?Core Java
Ans. TreeSet and TreeMap are used for maintaining sorted elements.

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   Like         Discuss         Correct / Improve     ordered collections  sorted collections     Asked in 1 Companies      basic        frequent

Frequently asked to Fresh graduates.
 Q867. Write a program to implement Binary search ?Core Java
Ans. http://algs4.cs.princeton.edu/11model/BinarySearch.java.html

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 Q868. Write a java program to implement Quick sort ?Core Java
Ans. http://www.programcreek.com/2012/11/quicksort-array-in-java/

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 Q869. Which is the root interface of Collection classes in Java ?Core Java
Ans. java.util.Collection

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 Q870. What are the disadvantages of multithreading ?Core Java
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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