4. Write a program in which the main method calls a method with the heading
public static char changeCase(char ch) that if ch is a
lowercase letter, the method will return the corresponding uppercase letter,
and if ch is a uppercase letter, the method will return the
corresponding lowercase letter. If ch is not a letter, the method
returns the same value of ch. Thus, for instance,
changeCase('a') returns A, changeCase('B') returns
b, and changeCase('3') returns 3. Note that the
uppercase letters have a unicode (ascii code) value that is 32 lower than the
corresponding lowercase ones.
Your main method should contain three calls to changeCase() for each case mentioned above.