JAVA

1. Java-overview 2. Features of Java 3. History of Java 4. HW SW Req for Java SE 7 5. Java Environment Setup 6. Basic Requirement 7. Comments 8. My First Program in Java 9. Line Break 10. Escape Sequences 11. Literals in Java 12. Identifiers in Java 13. Variables in Java 14. Data-Types in Java 15. Declare Variables 16. Reserved Key Words 17. printf() 18. Chained & Embedded state 19. Prog.to print sum of 2 nos 20. Scanner class 21. Prg.to print sum & average 22. Area & Perimeter of Rectangle 23. Area Circumference of Circle 24. Prg.for Simple Calculator 25. Operatos in Java 26. Ex. Of Operators 27. Swap two numbers 28. Hierarchy of Operators 29. if( ) statement 30. Prg.to check +ve,-ve or zero 31. if..else statement 32. Prg.to check Odd or Even 33. Prg.to print larger of 2 nos 34. Prg.to print largest of 3 nos 35. Prg.to check divisibility 36. Prg.to check print range 37. for. . . loop statement 38. prg.to print series of nos 39. Prg.to check divisibility 40. prg.to print sum of nos 41. Prg.to print Pyramid 42. prg.for Factorial 43. prg.to fill screen 44. prg.for largest/smallest no 45. prg.to print reverse no 46. prg.to add each digit 47. prg.for sum of series 48. prg.for fibonacci series 49. prg.to check Prime nos 50. prg. Prime no from 1 to 100 51. prg.Specified Prime nos 52. while( ) statement 53. do. . While statement 54. break & continue statement 55. switch case statement 56. Array in Java 57. print reverse order using array 58. Ascending/Descending order 59. prg.to search no in Array 60. Multidimensional Array 61. String in Java 62. String with spaces 63. prg.to print string in reverse 64. prg. to count A,E,I,O,U vowel 65. User defined methods 66. Methods program example 67. General Purpose Programs 68. Loan & EMI calculation prg. 69. Table print prg. 70. Leap year program 71. lower to UPPER case prg. 72. Age Distribution prg. 73. Bank note calculation prg. 74. Simple Interest prg. 75. Compound Interest prg. 76. Simple Depreciation prg. 77. Reducing bal.Depreciation prg. 78. Marksheet prg. 79. Income Tax prg. 80. Time calculator prg. 81. Distance converter prg. 82. Volume Air Calculation prg. 83. Time to fill Water Tank prg. 84. Salary Calculation prg. 85. Total Sale Calculation prg. 86. Male/Female percentage prg. 87. Library Rent prg. 88. Office Expance prg. 89. Total Salary Calculation prg. 90. Profit or Loss prg. 91. Total Profit/Loss prg. 92. Palindrome program 93. Java Interview Part1 94. Java Interview Part2 95. Java Interview Part3 96. Java Interview Part4 97. Java Interview Part5 98. Java Interview Part6 99. Java Interview Part7 100. Java Interview Part8 101. Java Interview Part9 102. Java Interview Part10 103. Java Interview Part11
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JAVA Interview Questions and Answers Part 5

 

41. Why do we need wrapper classes?

  • It is sometimes easier to deal with primitives as objects. Moreover most of the collection classes store

  • objects and not primitive data types. And also the wrapper classes provide many utility methods also. Because of these resons we need wrapper classes.

  • And since we create instances of these classes we can store them in any of the collection classes and pass them around as a collection. Also we can pass them around as method parameters where a method expects an object.

 

42. What are checked exceptions?

  • Checked exception are those which the Java compiler forces you to catch. e.g. IOException are checked Exceptions.

 

43. What are runtime exceptions?

  • Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input data or because of wrong business logic etc. These are not checked by the compiler at compile time.

 

44. What is the difference between error and an exception?

  • An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error. These JVM errors and you can not repair them at runtime.

  • While exceptions are conditions that occur because of bad input etc. e.g. FileNotFoundException will be thrown if the specified file does not exist.

  • Or a NullPointerException will take place if you try using a null reference. In most of the cases it is possible to recover from an exception (probably by giving user a feedback for entering proper values etc.).

 

45. How to create custom exceptions?

  • Your class should extend class Exception, or some more specific type thereof.

 

46. If I want an object of my class to be thrown as an exception object, what should I do?

  • The class should extend from Exception class. Or you can extend your class from some more precise

  • exception type also.

 

47. How does an exception permeate through the code?

  • An unhandled exception moves up the method stack in search of a matching When an exception is thrown from a code which is wrapped in a try block followed by one or more catch blocks, a search is made for matching catch block.

  • If a matching type is found then that block will be invoked. If a matching type is not found then the exception moves up the method stack and reaches the caller method. Same procedure is repeated if the caller method is included in a try catch block. This process continues until a catch block handling the appropriate type of exception is found. If it does not find such a block then finally the program terminates.

 

48. What are the different ways to handle exceptions?

  • There are two ways to handle exceptions,

    1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions.

    2. List the desired exceptions in the throws clause of the method and let the caller of the method hadle those exceptions.

49. What is the basic difference between the 2 approaches to exception handling.1. try catch block and 2. specifying the candidate exceptions in the throws clause? When should you use which approach?

  • In the first approach as a programmer of the method, you urself are dealing with the exception. This is fine if you are in a best position to decide should be done in case of an exception. Whereas if it is not the responsibility of the method to deal with it's own exceptions, then do not use this approach. In this case use the second approach.

  • In the second approach we are forcing the caller of the method to catch the exceptions, that the method is likely to throw. This is often the approach library creators use. They list the exception in the throws clause and we must catch them. You will find the same approach throughout the java libraries we use.

 

50. Is it necessary that each try block must be followed by a catch block?

  • It is not necessary that each try block must be followed by a catch block. It should be followed by either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be declared in the throws clause of the method.

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