Declarations and expressions so far have used the int type,
which is one of the main ones which programs use for internal computation. For
external communication with the user, programs use text, and often need to
declare variables which hold text, and use expressions which manipulate
text.
The type String is the one used in Java for variables which
hold text. It starts with a capital letter, unlike int, because
it is a compound type. There is a basic type char which holds a
single character, but a String consists of a sequence of
characters.
To get a fixed piece of text into a program, it has to have double quote
marks, e.g. "the answer is". This is a constant of
type String, just like 42 is a constant of type
int.
One of the most important operators for calculating with text in Java is the
+ operator. As well as being used to add numbers, it is also used
to "add" text, i.e. glue two pieces of text next to each other. For example,
"car" + "pet" gives "carpet".
More interestingly, Java's + operator also "adds" numbers to
text. If the first item is text, and the second is a number,
Java will convert the number to text before gluing the two things together.
For example, if you write "the answer is " + 42 then Java converts
the number 42 to the text "42" and glues the two
strings together to get "the answer is 42". The constant
"the answer is " needs the space at the end so that when the two
strings are glued together, you don't get "the answer is42"