Download Lecture 6 - Emory Math/CS Department

Lecture 8
Mixed type operations
• Automatic conversions
– (float and double)  double
– (byte, short, int)  int
– (byte, short, int, long)  long
• A computer can only operate on data of
the same data type
• The conversion rule is applied at the moment that
the arithmetic operation is performed
Today
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•
•
•
Expressions with mixed type variables
Increment operators
Characters
(new type)
Strings
(new type)
Numeric literals (constants)
• A numeric literal is a constant value that
appears in a Java program.
– 3.14159265358979 1776
– 2012
• Has type
• Demo Exercise3.java
Constant synax
• final datatype CONSTANT_NAME = value ;
Short hand operators
Assignment operator
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•
•
•
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=
// assignment operator
var = expr;
// syntax
Has lowest priority
c = b = a = 4 + 2;
// nested assignment
?
• Demo AssignExpr04.java
Increment / Decrement operators
• Difference between a++ and ++a
• The ++ and -- operators have higher priority than any binary
arithmetic operators in Java
• Demo Increment01.java
Character type (char)
• built-in (primitive) data type of Java
• is used to represent alpha-numerical information
(characters) inside the computer
• uses the Unicode to encode characters from
many different kinds of languages in the world
• uses 2 bytes of memory to store the Unicode
value
• represented as an integer
• The Unicode includes the ASCII code which is
used to encode English characters (recall HW1)
ASCII and Unicode
Why ‘quotes’?
• Character literals
– ‘a’
– ‘b’
– ‘c’
//
//
//
Unicode code value 97
Unicode code value 98
Unicode code value 99
• Without quotes will be confused with
identifier
‘a’ + 1 = ?
• Demo: Char01B.java
Syntax
• Define char variable
– char a;
// define variable a
• Assign a value
– a = ‘c’;
// store ASCII code
// of c in variable a
Printing difference int vs. char
Converting int  char
Converting lowercase to uppercase
Converting lowercase to uppercase
• Demo: Char05a.java
String
• A string is a sequence of characters enclosed
between the double quotes "...“
• Each character in a string is of the type char
and uses the Unicode as encoding method
• *not* a built in data type
String Class / Data type
• String Class ( online doc )
– Information
– Operations
// sequence of characters
// concatenation, sub-string, ..
String literals
• “Hello World”
• May contain escape character
– \n
– \t
// new line
// tab character
• The escape character is usually used to
express "unprintable" characters
Escape characters
Syntax
• String NameOfVariable ; // define string variable
• The class String announces the variable definition clause
• The NameOfVariable is an identifier which is the name of
the variable.
• A String typed variable can store the location
(address) of a sequence characters (string)
• Demo: String01.java
How strings are stored?
• “Hello”
• “Good bye”
//
//
5 characters
8 characters
• Can not fixed size variable
Location + length
Location + length
• Sentinel = a special character (symbol) that
denotes the end of a string
• The sentinel used in programming
languages to denote the end of a string is
usually the NULL character with Unicode
value 0.
Location + sentinel
String storage
• Which method is better?
– Location + length
– Location + sentinel