Use the following problems to test your object, immutability, and switch expression programming prowess. I strongly encourage you to give each problem a try before you turn to the solutions and download the example programs:

40. Checking null references in functional style and imperative code: Write a program that performs the null checks on the given references in a functional style and imperative code.
41. Checking null references and throwing a customized NullPointerException error: Write a program that performs the null checks on the given references and throws NullPointerException with custom messages.
42. Checking null references and throwing the specified exception (example, IllegalArgumentException): Write a program that performs the null checks on the given references and throws the specified exception.

43. Checking null references and returning non-null default references: Write a program that performs the null checks on the given reference, and if it is non-null, then return it; otherwise, return a non-null default reference.
44. Checking the index in the range from 0 to length: Write a program that checks whether the given index is between 0 (inclusive) and the given length (exclusive). If the given index is out of the [0, given length] range, then throw IndexOutOfBoundsException.
45. Checking the subrange in the range from 0 to length: Write a program that checks whether the given subrange [given start, given end] is within the bounds of the range from [0, given length]. If the given subrange is not in the [0, given length] range, then throw IndexOutOfBoundsException.
46. equals() and hashCode(): Explain and exemplify how equals() and hashCode() methods work in Java.
47. Immutable objects in a nutshell: Explain and exemplify what is an immutable object in Java.
48. Immutable string: Explain why the String class is immutable.
49. Writing an immutable class: Write a program that represents an immutable class.
50. Passing/returning mutable objects to/from an immutable class: Write a program that passes and returns a mutable object to/from an immutable class.
51. Writing an immutable class via the Builder pattern: Write a program that represents an implementation of the Builder pattern in an immutable class.
52. Avoiding bad data in immutable objects: Write a program that prevents bad data in immutable objects.
53. Cloning objects: Write a program that exemplifies shallow and deep cloning techniques.
54. Overriding toString(): Explain and exemplify practices for overriding toString().
55. switch expressions: Provide a brief overview of the switch expressions in JDK 12.
56. Multiple case labels: Write a snippet of code for exemplifying the JDK 12 switch with multiple case labels.
57. Statement blocks: Write a snippet of code for exemplifying the JDK 12 switch with case labels that point to a curly-braced block.