1. String

2. Review of String (1)
String is a user-defined class that is created by the programmers who implemented the Java library

3. Review of String (2)
 Defining String variables (object definition syntax):
The Java compiler recognize a short hand notation
for String creation:

4. How a String object is stored
A String is an object:

5. Instance methods on String (1)
The general format to use an operation on a String object:

6. Instance methods on String (2)
length(): returns the length of the string
charAt(n): returns the charcater at position n in the string

7. Instance methods on String (3)
substring(i,j): returns the substring from position i up to (not including) position j of the string
Concatenating strings:

8. Comparison operations
The == operator in Java always compare whether the value 
stored in variables are equal.
The test x == y does not test whether the strings stored in x and y are equal to one another

9. Comparing if strings are equal based on their content (1)
The instance method used to compare equality of two strings s1 and s2 based on their content:

10. Comparing if strings are equal based on their content (2)
The instance method used to compare equality of two strings s1 and s2 without considering upper/lower case difference:

11. Ranking 2 strings (1)
The instance method used to rank of two strings s1 and s2 
in alpha-numerical order:

12. Ranking 2 strings (2)
The instance method used to rank of two strings s1 and s2 
without considering upper/lower case in alpha- numerical order:

13. Finding substrings (1)
Finding (locate) the first occurrence of a substring sub in a string s:

14. Finding substrings (2)
The instance method used to find (locate) the last occurrence of a substring sub in a string s is:

15. Transformation Operations (1)
Transform all upper case letters in a string s into lower case letters
Transform all lower case letters in a string s into upper case letters

16. Transformation Operations (2)
Replace the first occurrence of a substring old inside a string s by the substring new
replace all occurrences of a substring old inside a string s by the substring new

17. Strings in Java are immutable
The instance methods in the String class do not change 
the implicit parameter (the string)

18. String and Array (1) a String is a single object
an array of char are a series (multiple) of variables
Converts a string into an array of char:

19. String and Array (2)
convert an array of char into a String object, we use a constructor method in the String class:

20. String and Array (3)
The chances are very good that the Java library contains 
instance methods that help you write your program