1. import java.util.List;
  3. public class ListValidator {
  5. /**
  6. * Validates a list for basic sanity checks.
  7. *
  8. * @param list The list to validate.
  9. * @param <T> The type of elements in the list.
  10. * @return True if the list is valid, false otherwise.
  11. */
  12. public static <T> boolean validateList(List<T> list) {
  13. if (list == null) {
  14. System.err.println("List is null.");
  15. return false;
  16. }
  18. if (list.isEmpty()) {
  19. System.err.println("List is empty.");
  20. return true; // Empty lists are considered valid by default
  21. }
  23. for (T element : list) {
  24. if (element == null) {
  25. System.err.println("List contains a null element.");
  26. return false;
  27. }
  28. }
  30. return true;
  31. }
  33. /**
  34. * Validates if all elements in a list are of the same type.
  35. * @param list The list to validate
  36. * @param <T> The type of the list elements
  37. * @return True if all elements are of the same type, false otherwise.
  38. */
  39. public static <T> boolean validateSameType(List<T> list) {
  40. if (list == null || list.isEmpty()) {
  41. return true; // Consider null or empty lists as valid
  42. }
  44. T firstElement = list.get(0);
  45. if (firstElement == null) {
  46. System.err.println("List contains a null element.");
  47. return false;
  48. }
  50. for (T element : list) {
  51. if (element == null) {
  52. System.err.println("List contains a null element.");
  53. return false;
  54. }
  55. if (!firstElement.getClass().equals(element.getClass())) {
  56. System.err.println("List contains elements of different types.");
  57. return false;
  58. }
  59. }
  60. return true;
  61. }
  63. /**
  64. * Validates if the list contains only positive numbers.
  65. * @param list The list to validate
  66. * @param <T> The type of list elements (must be Number)
  67. * @return True if all elements are positive numbers, false otherwise.
  68. */
  69. public static <T extends Number> boolean validatePositiveNumbers(List<T> list) {
  70. if (list == null) {
  71. System.err.println("List is null.");
  72. return false;
  73. }
  75. for (T element : list) {
  76. if (element == null) {
  77. System.err.println("List contains a null element.");
  78. return false;
  79. }
  80. if (element.doubleValue() <= 0) {
  81. System.err.println("List contains non-positive numbers.");
  82. return false;
  83. }
  84. }
  85. return true;
  86. }
  89. public static void main(String[] args) {
  90. // Example usage
  91. List<String> stringList = List.of("apple", "banana", "cherry");
  92. System.out.println("String list is valid: " + validateList(stringList));
  94. List<Integer> intList = List.of(1, 2, 3, 4, 5);
  95. System.out.println("Integer list is valid: " + validateList(intList));
  97. List<Object> mixedList = List.of(1, "hello", 3.14);
  98. System.out.println("Mixed list is valid: " + validateList(mixedList));
  100. List<String> nullList = null;
  101. System.out.println("Null list is valid: " + validateList(nullList));
  103. List<String> emptyList = List.of();
  104. System.out.println("Empty list is valid: " + validateList(emptyList));
  106. List<Integer> sameType = List.of(1, 2, 3, 4, 5);
  107. System.out.println("Same Type: " + validateSameType(sameType));
  109. List<Object> differentType = List.of(1, "hello", 3.14);
  110. System.out.println("Different Type: " + validateSameType(differentType));
  112. List<Double> positiveNumbers = List.of(1.0, 2.5, 3.0

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