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Interview Questions and Answers - Order By Newest

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Q31. Can a lock be acquired on a class ?

Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

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Q32. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?

Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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Q33. What is suspend() method used for ?

Ans. suspend() method is used to suspend the execution of a thread for a period of time. We can then restart the thread by using resume() method.

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Usually asked only to fresh graduates.

Q34. Difference between suspend() and stop() ?

Ans. Suspend method is used to suspend thread which can be restarted by using resume() method. stop() is used to stop the thread, it cannot be restarted again.

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Q35. What is the difference between System.console.write and System.out.println ?

Ans. System.console() returns null if your application is not run in a terminal (though you can handle this in your application)System.console() provides methods for reading password without echoing charactersSystem.out and System.err use the default platform encoding, while the Console class output methods use the console encoding

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Q36. Which load testing tools have you used ?

Ans. Rational Robot, JMeter, LoadRunner

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Q37. What data type Variable can be used in a switch statement ?

Ans. Variables used in a switch statement can only be a byte, short, int, or char ( and String with Java 7 and above )

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Q38. What is the Locale class?

Ans. The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region

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Q39. Difference between PATH and CLASSPATH ?

Operating System

Ans. PATH is the variable that holds the directories for the OS to look for executables. CLASSPATH is the variable that holds the directories for JVM to look for .class files ( Byte Code ).

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Rarely asked as default methods have been introduced with Java 8.

Q40. Can we have a default method without a Body ?

Ans. No. Compiler will give error.

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Q41. What is Closeable ?

Ans. A Closeable is an interface which is a source or destination of data that can be closed.

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Q42. Name few Locale classes and interfaces ?

Ans. http://www.buggybread.com/2015/01/java-locale-classes-and-interfaces.html

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Rarely asked as it was introduced with Java 8.

Q43. Which keyword specify that a variable is effectively final ? a. final b. No Keyword c. Both of the above d. None of the above

Ans. No Keyword

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Q44. What is RI or Reference Implementation ?

Ans. RI or Reference Implementation is a sample implementation provided for the API's / Specs, usually by their developers. This is usually a part of API documentation.

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Q45. What is GregorianCalendar class ?

Ans. This class provides support for traditional Western calendars.

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Q46. What is "Instance Initializer block" ?

Ans. Instance Initializer block is used to initialize the instance data member. It run each time when object of the class is created.

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Q47. Is it Necessary to send a POST request with the Payload or a body ?

Ans. No, we can also send an empty body with the POST Request.

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Q48. Can I hit the Rest Post Request through a browser address bar if it's not expecting any payload / body ?

Ans. No, even if there is no payload, you can't hit the POST request by typing it into browser address bar. You will need a client that can make a POST Request.

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Q49. 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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Usually asked with Questions related to Generics.

Q50. 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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Q51. 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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Q52. Is ++ or -- operation thread safe in Java ?

Ans. No

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Q53. 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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Q54. How can we catch an exception thrown by another thread ?

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

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Q55. What is serialVersionUID ?

Ans. Everytime an object is serialized the java serialization mechanism automatically computes a hash value by passing the meta information for the class. This id is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization

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Q56. Is there a way to know size of an object in Java ?

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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Q57. How does Java handle integer overflows and underflows?

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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Q58. Which memory segment holds String Pool in Java ?

Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

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Q59. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Ans. First will not create physical file in storage whereas the second will.

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Q60. What is Exception Wrapping ?

Ans. Exception wrapping is wrapping an exception object within another exception object and then throwing the outer exception.

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