CSMJava ProgrammingI Spring,2005

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Fundamental Data Types Lesson - 2
CSM-Java Programming-I
Spring,2005
2

• Objectives
• Review of last class.
• Identifiers and primitive data types.
• Operators.

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Identifiers

• Java identifiers are used for names of variables,
  constants and labels.
• They must start with a letter, a currency symbol
  or underscore (_) followed by letters, digits or
  both.
• Java language keywords cannot be used as
  identifiers. Eg int, private, void, new, for

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Primitive Types

• boolen either true or false
• char 16-bits
• byte 8-bits
• short 16-bits
• int 32-bits
• long 64-bits
• float 32-bits
• double 64-bits

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Literals

• A literal is a constant value that may be
  assigned to a primitive type.
• Boolean true and false
• Integer Integer constants are strings of octal,
  decimal or hexadecimal digits.
• E.g. 29-decimal
• 035-octal
• 0x1D, 0X1d-hexadecimal
• Suffix a L to indicate a long (64 bit) literal)

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Literals

• Floating-Point Floating point literals are
  expressed as decimal numbers.
• E.g. 18., 1.8e1, .18E2 all denote the same
  number.
• A floating-point literal with no F or D suffix
  defaults to double type.
• Character Character literals appear between
  single quotes. E.g. Q.

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Literals

• Character Certain special characters can be
  represented by an escape sequence. E.g. \n for
  newline, \t for tab, \b for backspace.
• Strings String literals appear between double
  quotes. E.g. Hi.
• A string literal references an object of type
  String.

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Strings

• Strings String is a sequence of characters.
  Strings are objects of the String class.
• The number of characters in a string is called
  the length of the string. Eg int n
  message.length()
• Strings can be concatenated, by using the
  operator.
• String name dave
• String message Hello, name
• Whenever one of the arguments of the operator
  is a string, the other argument is converted to a
  string.

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Strings

• If a string contains the digits of a number, use
  the Integer.parseInt or Double.parseDouble method
  to obtain the number value.
• Use the substring() method to extract a part of a
  string.
• Eg String greeting Hello World!
• String sub greeting.substring(0,4)
• //sub Hell
• String positions are counted starting with 0.

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final Keyword

• Any number that is not completely
  self-explanatory should be declared as a named
  constant.
• A final variable is a constant. Once its value
  has been set, it cannot be changed.
• Use named constants to make your programs easier
  to read and maintain.
• Eg final int DAYS_PER_YEAR 365

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static Keyword

• Java numbers are not objects, so you cannot
  invoke a method on a number. Eg To calculate
  sqrt or power.
• A static method does not operate on an object.
• Eg Math.sqrt(x) Math.round(y)

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Type Conversion

• When an assignment is made to a variable, the
  types of either side of the assignment must be
  compatible.
• Eg 1 double total a lot //Error
• Eg 2 int dollars 2
• double total dollars // Correct This is
  called implicit conversion.
• Eg 3 double dollars 2
• int total dollars // Error

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Type Conversion

• Eg 3 double dollars 2
• int total dollars // Error
• Casting You must convert the floating-point
  value to integer with a cast. (typename)
  expression
• int total (int) dollars

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Type Conversion

• Loss of Information
• Eg 1 double total 13.75
• int pennies (int)(total 100)
• Use the Math.round() method to round a
  floating-point number to the nearest integer to
  avoid the loss of information.

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Operators

• Arithmetic Operators
• , -, , /, (remainder)
• If both the arguments of the / operator are
  integers, the result is an integer and the
  remainder is discarded. Eg 7/4 1 3 is
  discarded.

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Operators

• Arithmetic Operators
• , -, , /, (remainder)
• Eg 7.0/4.0, 7/4.0, 7.0/4 all yield 1.75
• The operator computes the remainder of a
  division. Eg 7 4 3

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Common Errors

• Integer Division
• Eg int s1 5
• int s2 6
• double avg (s1 s2) / 3 // Error
• double avg (s1 s2) / 3.0 //Correct
• Unbalanced Parentheses
• 1.5 ((- (b Math.sqrt(bb 4ac)) / (2a))

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Operators

• Increment and decrement Operators
• , --
• i is equivalent to i i1
• Increment and decrement operators can be either
  prefix of postfix operators (they can appear
  either before or after what they operate on).

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Increment and decrement Operators

• If increment or decrement operators appear before
  (prefix), the operation is applied before the
  value of the expression is returned.
• If increment or decrement operators appear after
  (postfix), the operation is applied after the
  value of the expression is used.

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Example Increment and decrement Operators

• public class Ex1
• public static void main(String args)
• int x 10
• System.out.println(x)
• System.out.println(x)
• System.out.println(x)

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Relational and Equality Operators

• gt greater than
• gt greater than or equal to
• lt less than
• lt less than or equal to
• equal to equality op.
• ! not equal to equality op.
• The unary operator ! Inverts a boolean !true is
  same as false
• Equality operators opearte only on boolean values

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Logical Operators

• - conditional AND
• - conditional OR

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Example1 Logical Operators

• if (x y)
• if (y z)
• Do something
• The inner if is executed only if both x and y are
  true. If x is false, y is not evaluated.
• The body of inner if is excecuted if either y or
  z is true. If y is true, z is not evaluated.

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Ternary Operator

• x (a ? b c) is equivalent to
• if (a)
• x b
• else
• x c

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Assignment Operator

• a 10
• Same as
• a a10
• Same for all arithmetic operators

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Operator Precedence

• The order of precedence of operators from highest
  to lowest is
• postfix ,., (params), expr, expr
• Unary expr, expr, expr, expr !
• Multiplicative /
• Additive -
• Relational lt, gt, lt, gt
• Equality , !
• Logical AND
• Logical OR
• Ternary ?
• Assignment , , -, , /,

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Operator Precedence

• Operators with the same precedence appear on the
  same line in the table.
• Precedence can be overridden using parentheses
• Operands to the operators will be evaluated
  left-to-right, except for , , ?. Eg xyz.
  First evaluates x, then y, adds the values
  together, evaluates z and adds that to the
  previous result.

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