CSC 313 Java Chapter 2 Data Types Notes to accompany Beginning Java 2 by Ivor Horton

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CSC 313 JavaChapter 2 Data Types Notes to
accompany Beginning Java 2 by Ivor Horton
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Java Data Types

• Java has two kinds of types
• fundamental, primitive or simple
• derived or composite
• No variable can be used until it is defined.
• Java is a strongly typed language.
• Sun Tutorial on Data Types

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Java Primitive Data Types
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Data Types, Default Values

• No variable can have an undefined value.
• Instance or class variables are implicitly
  initialized to a standard default value.
• Local variables are not implicitly initialized to
  a default value and must be explicitly
  initialized.

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Identifier Names

• An identifier can be any length, but it must
  start with a letter, an underscore, or a dollar
  sign.
• The rest of an identifier can include any
  characters except those used as operators in Java
  (such as , -, or ).
• It is generally better if you stick to letters,
  digits, and underscore characters.
• Java is a case-sensitive language

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Integer Variables

• Declaring and Initializing
• int myNumber 12345
• byte luckyNumber 7
• short smallNumber 1234
• long bigOne 999999999L
• long big 999999999L, largeNum 100000000L
• long xCoord0L, yCoord0L

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Decimal Constants

• A decimal constant must not begin with a 0. An
  octal constant begins with a 0 and a hexadecimal
  constant begins with 0x or 0X.
• The java.math package has a BigInteger class for
  arbitrary-precision integer arithmetic.

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Floating-point types

• The floating-point types are float (32 bits) and
  double (64 bits).
• A floating-point constant such as 3.14 is of type
  double, whereas 3.14F and 3.14f are of type
  float.

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Floating point Variables

• As with integer calculations, floating point
  calculations in Java will produce the same
  results on any computer. Declaring and
  Initializing
• double sunDistance 1.496E8
• float hisWeight 185.2F

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Mixed Arithmetic Expressions

• The way mixed expressions are treated is
  governed by some simple rules that apply to each
  operator in such an expression. The first rule
  that applies is the one that is used
• If either operand is of type double, the other is
  converted to double before the operation is
  carried out.
• If either operand is of type float, the other is
  converted to float before the operation is
  carried out.
• If either operand is of type long the other is
  converted to long before the operation is carried
  out.
• If neither operand is double, float or long, they
  must be int, short, or byte, so they use 32-bit
  arithmetic.

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Mathematical Functions

• Java provides a range of methods that support
  such functions as part of the standard library
  stored in the package java.lang, and all these
  are available in your program automatically.
• The methods that support various additional
  mathematical functions are implemented in the
  class Math.
• To reference a particular function you need to
  write Math and a period in front of the function
  name. To use sqrt(), which calculates the square
  root of whatever you place between the
  parentheses, you would write
  Math.sqrt(aNumber)

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Mathematical Functions

• Sun Documentation
• Math class

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Explicit Casting

• Sometimes the default treatment of mixed
  expressions is not what you want. For example, if
  you have a double variable result, and you
  compute its value using two int variables three
  and two with the values 3 and 2, with the
  statement,
• result  1.5  three/two
• the value stored will be 2.5. You may have wanted
  the term three/two to produce the value 1.5 so
  the overall result would be 3.0. You could do
  this using an explicit castresult  1.5  (doubl
  e)three/two

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Explicit Casting

• This causes the value stored in three to be
  converted to double before the divide operation
  takes place. Then rule 1 applies for the divide
  operation, and the operand two is also converted
  to double before the divide is executed.
• Hence the value of result will be 3.0.

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Explicit Casting

• You can cast any of the basic types to any other,
  but you need to take care that you don't lose
  information when you do so.
• Casting from a larger integer type to a smaller
  has the potential for losing information, as does
  casting any floating point value to an integer.
• Casting from double to float can also produce
  effective infinity when the original value is
  greater than 1038.

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boolean Variables

• Recall that boolean expressions evaluate either
  true of false.
• You can use boolean variables to store the result
  of evaluating a boolean expression boolean
  midDay (hour 12)
• Unlike C you can not assign a numeric value to
  boolean data, although you can use the values of
  true false. boolean flag false

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Casting

• In a cast operation, the target type is enclosed
  in parentheses.
• Some restrictions imposed on casts. For example,
  a boolean value such as true cannot be cast to
  any other type, and no nonboolean value can be
  cast to boolean.
• Casts should be used with great caution.

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Data type char

• char variables can store any character in the
  Unicode character set
• This includes any keyboard character in addition
  to many others.
• You must enclose char values in single quotes
• E.g. b, 1,
• E.g. char letter a
• Some special Unicode characters are known as
  escape sequences
• E.g. \n is the new-line character

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Thats All Folks!