Java Selection Statements

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Java Selection Statements
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Summary

• Operators
• Algorithm Design Languages
• Selection Statements
• single selection statement
• double selection statement
• multiple selection statement

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Operators

• An expression consists of operand(s) and
  operator(s) (also called arguments) that specify
  the operation between the operands to execute the
  expression
• The process of applying the operators to the
  operands is called expression evaluation, e.g.
  for numeric expressions expression evaluation is
  equivalent to calculating the result value of the
  expression
• An expression has a result value type which
  depends on the operands types and operators that
  take part in the expression

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Operators (2)

• Examples of numeric expressions in Java
• 43 7 3.5/7 5.68.9 ( 9-7 ) (
  35-27 ) 9-735-27
• There are 3 types of operators depending on the
  number of the operands
• unary - one operator, one operand
• binary- one operator, two operands
• ternary- one operator, three operands

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Operators (2)

• Precedence is the order in which an expression is
  evaluated
• Some operators have precedence higher than
  others e.g. you evaluate the multiplication first
  and then the addition
• You can use parentheses to change the order of an
  expression evaluation
• Associativity
• left to right or right to left
• Depending on the data type you can have different
  operations
• Examples
• Numeric data types - / etc.
• Boolean data types !

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Operators Types

• Depending on the operands types and the operator
  between them there are 4 operators types
• Arithmetic Operators
• Relational Operators
• Logical Operators
• Conditional Operator

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Relational Operators
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Relational Operators - Examples

• int i1 15 // first operand
• int i2 6 // second operand
• boolean result // the result
• result i1 i2
• result i1 ! i2
• result i1 lt i2
• result i1 lt i2
• result i1 gt i2
• result i1 gt i2

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Relational Operators - Examples

• int i1 15 // first operand
• int i2 6 // second operand
• boolean result // the result
• result i1 i2 // result false
• result i1 ! i2 // result true
• result i1 lt i2 // result false
• result i1 lt i2 // result false
• result i1 gt i2 // result true
• result i1 gt i2 // result true

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Relational Operators Precedence
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Characters

• A char variable stores a single character from
  the Unicode character set
• A character set is an ordered list of characters,
  and each character corresponds to a unique number
• Unicode is an international character set,
  containing symbols and characters from many world
  languages
• The Unicode character set uses 16 bits per
  character, allowing for 65,536 unique characters
• Character literals are enclosed in single quotes
• A' c' 3' '' .' '\n
• For more information go to http//unicode.org

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Characters (2)

• You might have heard about the ASCII character
  set
• ASCII is older and smaller than Unicode, but is
  still quite popular
• The ASCII characters are a subset of the Unicode
  character set, including
• uppercase letters A, B, C,
• lowercase letters a, b, c,
• digits 0, 1, 2,
• special symbols , , , ?,
• control characters backspace \b
• (escape sequences) new line \n,
• For more information go to http//www.asciitable.c
  om/

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Escape Sequences in Java
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Booleans

• Represent two values switched on, switched off
• Two reserved words for boolean values true and
  false

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Logical Operators

• Logical Operators - a Table
• Truth Tables for Logical Operators
• Arithmetic, Relational Logical Operators
  Precedence
• Logical Operators - an Example

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Logical Operators a Table
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Truth Table for Logical Operators
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Truth Tables for Logical Operators
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Relational Logical Operators Precedence
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Logical Operators - an Example
int i1 20, i2 7, i3 7
boolean result result !(i1 i2)
result i1 ! i2 // same as
!(i1 i2) result i1 i3
result i1 gt i2 i1 i3
result i1 gt i2 i1 i3
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Logical Operators - an Example
int i1 20, i2 7, i3 7 //
operands boolean result result
!(i1 i2) // result true
result i1 ! i2 // result true
result i1 i3 // result
false result i1 gt i2 i1 i3 //
result false result i1 gt i2 i1 i3
// result true
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Conditional Operator

• Ternary if-else operator
• 
  false
• booleanExpr ? expr1 expr2
• Example true
• int i 7
• int result
• result i lt 10 ? i 100 i 10
• // result i 100 700

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Algorithm

• An algorithm is a set of steps (rules) for
  solving a problem in terms of
• actions to be executed
• the order of actions execution
• We are using programming languages to specify the
  steps in an algorithm
• actions are called statements
• the order of statement execution is called
  program control

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Algorithm Design Methods

• Algorithm design - special languages to help the
  programmer develop algorithms
• The program performing the algorithm steps can
  then be written in any programming language
• Algorithm Design Languages

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Algorithm Design Languages

• Program Design Language (PDL) Structured
  English Pseudocode
• artificial and informal language that helps
  programmers develop algorithms
• Flowcharts
• graphical language for representation of
  algorithms

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PDL Notation
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Flowcharts
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Flow of Control

• The order of statement execution in a program or
  method is called the flow of control
• Unless specified otherwise, the order of
  statement execution is linear one statement
  after the other in sequence
• Some programming statements modify that order,
  allowing us to
• decide whether or not to execute a particular
  statement, or
• repeat a statement execution over and over
• These decisions are based on conditions in the
  program that evaluates to true or false

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Selection Statements

• A selection statement lets us choose which
  statement will be executed next
• Selection statements are sometimes called
  conditional statements
• Selection statements give us the power to make
  decisions and branch the program execution
• Java's selection statements are
• the if statement
• the if-else statement
• the switch statement

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Selection Statements

• Single Selection
• the if statement
• Double Selection
• the if/else statement
• Multiple Selection
• the switch statement

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Single Selection Statement

• if ( booleanExpr ) statement
• Example
• It is raining outside. Take your umbrella.
• Flowchart

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The if Statement Execution

• First the condition (represented by booleanExpr)
  is evaluated.
• If it is true, the statement is executed.
• If the condition is false - the next statement
  after the if is executed.

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The if statement (3) - Examples

• if ( countNumbers 10 ) System.out.println( )
• if ( grade gt 90 )
• System.out.println( You are an excellent
  student! )
• if ( account lt creditLimit )
• System.out.pritnln( You have insufficient
  credit! )
• if ( dayOfTheWeeek gt 5 )
• System.out.println( Time to relax )
• System.out.println( Weekend.)

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Double Selection Statement

• if( booleanExpr )statement1 else statement2
• Example
• If you are hungry - go for lunch, otherwise take
  a cup of coffee.
• Flowchart

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The if/else Statement Execution

• First the condition (represented by booleanExpr)
  is evaluated.
• If it is true, the statement1 is executed.
• If the condition is false - the statement2
  (after else) is executed.
• The next statement after the if is executed.

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The if/else Statement Examples

• if ( dayOfTheWeek gt 5 )
• System.out.println( Weekend.)
• System.out.println( Time to relax )
• else
• System.out.println( Workday.)
• System.out.println( Go to work! )

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Embedded if/else Statement

• char grade A
• if ( grade A)
• System.out.println( Excellent student)
• else
• if ( grade B )
• System.out.println( Good student)
• else
• if ( grade C )
• System.out.println( Average student)
• else
• if ( grade D )
• System.out.println( Bad student)
• else System.out.println(Failed student)

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Multiple Selection Statement

• switch ( Expression )
• case value1 statement1 break
• case value2 statement2 break
• case valueN statementN break
• default statementD break

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Multiple Selection Statement Flowchart
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The switch Statement Execution

• First the expression is evaluated.
• The value of the expression is compared with the
  value in the first case (value1). If they are
  equal, the statement1 is executed.
• If they are not equal than the value of the
  expression is compared with the value in the
  second case (value2). If they are equal, the
  statement2 is executed and so on.
• If the value of the expression is not equal to
  any of the values (in cases) the statementD (the
  default case) is executed.
• The next statement after the switch is executed.

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The switch Statement Example

• switch ( grade )
• case A System.out.println( Excellent
  student)
• break
• case B System.out.println( Good student)
• break
• case C System.out.println( Average
  student)
• break
• case D System.out.println( Bad student)
• break
• default System.out.println(Failed
  student)
• break