Period don't support method chaining, only the last one in the chain takes effect.
For example, Period p = Period.ofDays(1).ofDays(10).ofDays(1); is equivalent to Period p = Period.ofDays(1);
DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT) or DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT) are all ok to format LocalDateTime, the first just print date part, the second just print time part.
java throws run time exceptions when invalid values are supplied to LocalDate.of(int year, int month, int dayOfMonth).
Array didn't implement equals, ArrayList implemented equals
Integer.parseInt("4") returns an int.
Integer.valueOf("4") returns an Integer.
When sort strings, number goes first, then upper case letter, then lower case letter.
Convert from an Array to an ArrayList use static method Arrays.asList(array).
An array must be sorted in order to have Arrays.binarySearch(array, number) to return a predictable value.
An array have array.length, an ArrayList have arrayList.size(), a String and StringBuilder have str.length() and sb.length()
It is legal to leave out the size for later dimensions of a multidimensional array, the first one is required.
A String concatenated with any other type gives a String, "a" + 12.1 is a12.1, "a" + false is afalse.
String is immutable, StringBuilder is mutable, StringBuffer is mutable, Array is mutable, ArrayList is mutable.
