Top 100 Questions for Java Developer
### Basic Syntax and Variables
1. Write a program to print "Welcome to Java" to the console.
2. Write a program to add two numbers entered by the user.
3. Write a program to swap two numbers using a temporary variable.
4. Write a program to check if a number is positive, negative, or zero.
5. Write a program to calculate the area of a circle given its radius.
6. Write a program to convert Celsius to Fahrenheit.
7. Write a program to find the remainder of two numbers without using % .
8. Write a program to check if a year is a leap year.
9. Write a program to calculate the average of three numbers.
10. Write a program to print the ASCII value of a character.
### Loops and Control Flow
11. Write a program to print numbers from 1 to 100.
12. Write a program to print all even numbers between 1 and 50.
13. Write a program to calculate the sum of the first n natural numbers.
14. Write a program to print the reverse of a number.
15. Write a program to find the factorial of a number using a loop.
16. Write a program to print a pattern of stars (e.g., a right triangle).
17. Write a program to check if a number is a palindrome.
18. Write a program to find the sum of odd numbers between 1 and 100.
19. Write a program to generate a multiplication table from 1 to 10.
20. Write a program to count the number of digits in a number.
### Arrays
21. Write a program to find the sum of all elements in an array.
22. Write a program to find the minimum element in an array.
23. Write a program to reverse an array without using a second array.
24. Write a program to sort an array in descending order.
25. Write a program to find duplicate elements in an array.
26. Write a program to rotate an array to the right by k steps.
27. Write a program to find the average of elements in an array.
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28. Write a program to check if an array contains a specific element.
29. Write a program to merge two arrays into a single array.
30. Write a program to find the second smallest element in an array.
### Strings
31. Write a program to count the number of characters in a string.
32. Write a program to reverse a string using a loop.
33. Write a program to check if two strings are equal (case-sensitive).
34. Write a program to remove all spaces from a string.
35. Write a program to convert a string to lowercase without built-in methods.
36. Write a program to find the first non-repeating character in a string.
37. Write a program to check if a string is an anagram of another string.
38. Write a program to count the number of words in a sentence.
39. Write a program to replace all vowels in a string with ‘*’.
40. Write a program to concatenate two strings without using + .
### Object-Oriented Programming (OOP)
41. Write a program to create a Student class with name and age attributes.
42. Write a program to calculate the area of a rectangle using a class.
43. Write a program to demonstrate constructor overloading in a Box class.
44. Write a program to implement method overriding with a Dog class extending Animal .
45. Write a program to create an abstract Vehicle class with a Car subclass.
46. Write a program to implement an interface Shape with a Square class.
47. Write a program to demonstrate encapsulation with a BankAccount class.
48. Write a program to create a Person class with a static counter for objects created.
49. Write a program to simulate a TrafficLight class with color changes.
50. Write a program to create a Point class with methods to calculate distance.
### Exception Handling
51. Write a program to handle an ArrayIndexOutOfBoundsException .
52. Write a program to validate user input (e.g., age must be positive).
53. Write a program to catch and handle a NumberFormatException .
54. Write a program to throw a custom exception for invalid password length.
55. Write a program to use try , catch , and finally in a division operation.
56. Write a program to handle multiple exceptions (e.g., division by zero and null input).
57. Write a program to check if a file exists, handling FileNotFoundException .
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58. Write a program to simulate a login system with exception handling.
59. Write a program to handle an exception when parsing a string to an integer.
60. Write a program to propagate an exception up the call stack.
### Collections
61. Write a program to add 10 integers to an ArrayList and print them.
62. Write a program to remove even numbers from an ArrayList .
63. Write a program to sort a LinkedList of strings.
64. Write a program to store key-value pairs in a HashMap and retrieve them.
65. Write a program to check if an element exists in a HashSet .
66. Write a program to find the intersection of two ArrayList s.
67. Write a program to reverse a LinkedList .
68. Write a program to count occurrences of elements using a HashMap .
69. Write a program to convert an ArrayList to an array.
70. Write a program to iterate over a HashMap using a loop.
### Recursion
71. Write a recursive program to calculate the sum of digits in a number.
72. Write a recursive program to reverse a string.
73. Write a recursive program to find the power of a number (e.g., x^n).
74. Write a recursive program to print the Fibonacci series up to n terms.
75. Write a recursive program to calculate the GCD of two numbers.
### Input/Output (I/O)
76. Write a program to read an integer from the user using Scanner .
77. Write a program to write a string to a file using FileWriter .
78. Write a program to read and display the contents of a file.
79. Write a program to count the number of characters in a file.
80. Write a program to append text to an existing file.
81. Write a program to copy contents from one file to another.
82. Write a program to read a CSV file and print its contents.
83. Write a program to check if a file exists and create it if it doesn’t.
84. Write a program to delete a file if it exists.
85. Write a program to read multiple lines from the console until "exit" is entered.
### Miscellaneous
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86. Write a program to check if a number is an Armstrong number.
87. Write a program to generate the first n prime numbers.
88. Write a program to find the sum of elements in a 2D array.
89. Write a program to implement a simple calculator using methods.
90. Write a program to simulate a dice roll using Random .
91. Write a program to convert decimal to binary without built-in methods.
92. Write a program to find the largest element in a 2D array.
93. Write a program to check if a matrix is symmetric.
94. Write a program to implement a basic stack using an array.
95. Write a program to implement a queue using an array.
96. Write a program to find the LCM of two numbers.
97. Write a program to simulate a bank ATM with withdraw and deposit options.
98. Write a program to generate a random password of length 8.
99. Write a program to check if a string contains only digits.
100. Write a program to sort a list of names alphabetically.
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