String
Review of String (1)
• String is a user-defined class that is created by
the programmers who implemented the Java library
Review of String (2)
•
Defining String variables (object definition syntax):
• The Java compiler recognize a short hand notation
for String creation:
How a String object is stored
• A String is an object:
Instance methods on String (1)
• The general format to use an operation on a String object:
Instance methods on String (2)
• length(): returns the length of the string
• charAt(n): returns the charcater at position n in the string
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:
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
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:
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:
Ranking 2 strings (1)
• The instance method used to rank of two strings s1 and s2
in alpha-numerical order:
Ranking 2 strings (2)
• The instance method used to rank of two strings s1 and s2
without considering upper/lower case in alphanumerical order:
Finding substrings (1)
• Finding (locate) the first occurrence of a substring sub in
a string s:
Finding substrings (2)
• The instance method used to find (locate) the last occurrence
of a substring sub in a string s is:
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
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
Strings in Java are immutable
• The instance methods in the String class do not change
the implicit parameter (the string)
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:
String and Array (2)
• convert an array of char into a String object, we use
a constructor method in the String class:
String and Array (3)
• The chances are very good that the Java library contains
instance methods that help you write your program