Identifiers and types
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Identifiers and Types: Understanding Variables and Data Types in Java, Slides of Java Programming
An introduction to identifiers and data types in java programming. It covers the rules for naming identifiers, the different primitive types (boolean, char, int, long, float, double), and the differences between int and long, float and double. It also explains the concept of integer division and how to fix it through typecasting.
Typology: Slides
2012/2013
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Identifiers and types
Announcements
Emails in office hours, feel free to set up meeting via email JavaScript vs Java?
Identifiers
Identifiers
An identifier is the name of a variable (or object, class, method, etc.) int sum type identifier
- Case sensitive
- Must use only letters, numbers or _
- Cannot start with a number
- (Some reserved identifiers)
Identifiers
- james parker
- BoByBoY
- x
- 3x
- x_______
- _______x
- Home.Class
- Five%
- x- Which identifiers are valid?
Identifiers
boolean
Many other languages allow conversion between integer and boolean True = 1 and false = 0 Java does not allow this
int vs long?
int - Whole numbers in the approximate range: -2.14 billion to 2.14 billions ( 9 ) long - Whole numbers in the approximate range: -9.22 quintillion to 9.22 quintillion ( 18 ) Using int is standard (unless you really need more space, for example scientific computing)
float vs double?
float is now pretty much obsolete. double takes twice as much space in the computer and is 1) more accurate and 2) more precise Bottom line: use double (unless for a joke)
float and double
Both stored in scientific notation double x = 2858291; Computer's perspective: x = 2.858291e or x = 2.858291 * 10 6
Numerical analysis
Field of study for (reducing) computer error See: SubtractionError.java Can happen frequently when solving system of linear equations
int or double?
If you are counting something (money), use int If you are dealing with abstract concepts (physics), use double int doesn't make “rounding” mistakes Non-primitive types exist for both int and double for more expression/precision
Primitive type hierarchy
int x; double y; x+y int x; int y; x/y Converted to double Not converted (still int)
Integer division
See: SimpleDivision.java Can be fixed by typecasting: (double)1/