The String class in Java

What is a string?

Let's start with a few examples of strings: "Apple", "Java", "Orange",
"Dream", etc.

In Java as in most other programming languages, strings are
represented as a text enclosed with a pair of double quotes in syntax
(Well, Python uses single quotes and double quotes, but Java only used
double quotes.)

Meaning of a string is whatever meaning that you as a programmer
give to the string.  For example, I might use "Apple" in my program to
mean the fruit we eat or the computer company named Apple.   Perhaps,
I might use "apple" to mean fruit and "Apple" to mean the computer
company.

How a string is represented in memory is up to the language we happen
to be using.  In Java a string is represented as an array of
characters.  For example, the string "Dream" is represented as an
array looking like this: 

         +---+---+---+---+---+
         |'D'|'r'|'e'|'a'|'m'|
         +---+---+---+---+---+
           0   1   2   3   4

java.lang.String is a class already defined in the language.  It is
NOT a primitive data type.  It is instead a compound data type, a
sequence of characters represented (implemented) as an array.

We combine primitive data type values to form compound data type
values.  So, by combining characters as a sequence, we form a string. 

We will form a data type named, say Student, later by combining
multiple primitive data types and even other compound data types,
e.g., an int representing student ID, a double representing GPA, a
string representing student name, and yet another string representing
student's address.  We will see how to do this when we create our own
classes later.

For now, let's study strings in a little more detail.

. see StringTest.java

. 'split' function on java.lang.String

  - see SplitTest.java

  When you are given a long string, you can split it into meaningful 
  chunks and process the chunks as you see fit.  SplitTest.java shows
  an example of one such usage.  You will find this example quite
  useful as you deal with strings, or a long text file later.