Control%20Statements

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Chapter - 2
Control Statements
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This chapter includes -

• Selection Statements
• if statement
• if-else-then statement
• switch statement
• Iteration Statements
• while statement
• Do-while statement
• for statement
• Jump statements
• Break statements
• Continue statement
• Return statement

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Control Statements

• Javas control statements are nearly identical to
  those in C/C.
• However there are few differences - especially in
  the break and continue statement

Selection Statements

• Java supports two selection statements if and
  switch
• The general form of Javas if statement is
• if (condition) statement1
• else statement2
• Each statement may be a single statement or a
  compound statement enclosed in curly braces (that
  is, a block).
• The else clause is optional.
• The if works like this If the condition is
  true, then statement1 is executed. Otherwise,
  statement2 (if exists) excutes.

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Nested if Statements

• Nested ifs are very common in programming.
• An else statement always refers to the nearest if
  statement that is within the same block.
• Here is an example
• if(i 10)
• if(j lt 20) a b
• if(k gt 100) cd
• else a c // associated with the if(k gt
  100)
• else a d // this else refers to
  if(i 10)

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The if-else-if Ladder

• Let us follow the example below to understand the
  if-else-if Ladder
• class IfElse
• public static void main(String arg )
• int month 4 // April
• String season
• if(month 12 month 1 month
  2)
• season Winter
• else if(month 3 month 4 month
  5)
• season Spring
• else if(month 6 month 7
  month 8)
• season Summer
• else if(month 9 month 10 month
  11)
• season Authum
• else
• season Bogus Month)
• System.out.println(April is in the season
  .)

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switch Statement

• The general form is
• switch (expression)
• case value1
• // statement sequence
• break
• case value2
• // statement sequence
• break
• .
• .
• case valueN
• // statement sequence
• break
• default
• // default statement sequence

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An Example of switch Statements

• Let us follow the example below to understand the
  use of switch
• class SampleSwitch
• public static void main(String arg )
• for(int i 0 i lt 4 i)
• switch(i)
• case 0
• System.out.println( i is zero)
• break
• case 1
• System.out.println( i is one)
• break
• case 2
• System.out.println( i is two)
• break
• default
• System.out.println( i is greater than
  2)

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Structure of Nested switch Statements
switch(count) case 1 switch(target)
case 0 System.out.println( target
is zero) break case 1
System.out.println( target is
one) break default System.out.prin
tln( i is greater than 2)
break case 2 //
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Iteration Statements

• Javas iteration statement are for, while, and
  do-while.
• These statements create what we commonly call
  loops.

while Statements

• It repeats a statement or block while its
  controlling expression is true.
• The general form of while statement is
• while (condition)
• // body of the loop
• The condition can be any Boolean expression. The
  body of the loop will be executed as long as the
  conditional expression is true.
• EXAMPLE class WhileDemo
• public static void main(String arg )
• int n10
• while (ngt0)
• System.out.println(n n)
• n - -

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do-while statement

• You might have noticed that if the conditional
  expression controlling a while loop is initially
  false, then the body of the loop will not be
  executed at all.
• The do-while loops always executes its body
  atleast once, because its conditional expression
  is at the bottom of the loop.
• The general for of do-while statements is as
  follows
• do
• // body of loop
• while (expression)
• If the expression is true the loop will repeated.
  Follow the example
• class DoWhileDemo
• public static void main(String arg )
• int n10
• do
• System.out.println(n n)
• n - -
• while (n gt 0)

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for statement

• The general for of do-while statements is as
  follows
• for(initialization condition iteration)
• // body
• The for loop operates as follows. When the loop
  first starts, the initailization portion of the
  loop is executed.
• This is an expression that sets the value of the
  loop control variable.
• Next condition is evaluated. This must be a
  Boolean expression.
• If the expression value is true, then the body of
  the loop is executed.
• Next, the iteration portion of the loop is
  executed.
• Follow the example
• class ForDemo
• public static void main(String arg )
• int n
• for (n10 ngt0 n - -)
• System.out.println(n n)

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Using the Comma in for statement

• To allow two or more or more variables to control
  a for loop, Java permits you to include multiple
  statements in both the initialization and
  iteration portion of the for.
• Let us follow the example
• int a, b
• for(a 1, b 4 altb a, b - - )
• System.out.println(a a)
• System.out.println(b b)

Nested for Loops
int i, j for(i 0 ilt10 i ) for(j
0 jlt10 j ) System.out.print ( .
) System.out.println( )
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Variation in for statement

• VARIATION 1
• The condition controlling the for can be any
  Boolean Expression.
• Follow the example below
• boolean done false
• for(int i 1 !done i)
• // ..
• if(interrupted( )) done true
• VARIATION 2
• Either the initialization or the iteration
  expression or both may be absent.
• Int i0
• boolean done false
• for( !done )
• // ..
• i
• if(i 10) done true

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Jump statement

• Java supports three jump statements break,
  continue and return.
• These statements transfer control to another part
  of your program.

Using Break

• In Java, the break statement has three uses.
• First as you have seen, it terminates a statement
  sequence in a switch statement.
• Second, it can be used to exit a loop.
• Third, it can be used as a civilized form of
  goto.
• USING BREAK TO EXIT A LOOP
• for(int i0 i lt 100 i)
• if(i 10) break // terminates loop if i
  10
• System.out.println(i i)
• System.out.println(loop complete.)
• break statement can be used with any of javas
  loops, like while loop.
• When used inside a set of nested loops, the break
  statement will only break out of the innermost
  loop.

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Using Break As a form of GOTO

• Java defines an expanded form of the break
  statement.
• By using this form of break statement, you can
  break out of one or more blocks of code. This
  form of block works with label.
• class BreakInvalidDemo
• public static void main(String arg )
• one for(int i 0 ilt3 i)
• System.out.println(Pass i )
• for(int j 0 jlt3 j)
• if ( j 10) break one // WRONG
• System.out.print( j )

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Using Break As a form of GOTO (Continued)

• Keep in mind that you can not break to any label
  which is not defined for an enclosing block.
• For example, the following program is invalid and
  will not compile.
• class BreakDemo
• public static void main(String arg )
• boolean t true
• first
• second
• third
• System.out.println(Before break)
• if(t) break second
• System.out.println(This wont
  execute)
• System.out.println(This wont execute)
• System.out.println(This is after second
  block)

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Continue Statement

• In while and do-while loops a continue statement
  causes control to be transferred directly to the
  conditional rxpression that controls the loop.
• In a for loop, control goes first to the
  iteration portion of the for statement and then
  to the conditional expression.
• Follow the example below
• class ContinueDemo1
• public static void main(String arg )
• for (int i0 ilt10i)
• System.out.print(i )
• if(i2) continue
• System.out.println( )

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Continue Statement (continued)

• As with the break statement, continue may specify
  a label to describe which enclosing loop to
  continue.
• class ContinueDemo
• public static void main(String arg )
• outer for (int i0 ilt10i)
• for(int j0jlt10j)
• if(jgt1)
• System.out.println( )
• continue outer
• System.out.println((i j))
• System.out.print( )

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return Statement

• The return statement is used to explicitly return
  from a method.
• class ReturnDemo
• public static void main(String arg )
• boolean t true
• System.out.println(before return statement
  )
• if(t) return
• System.out.println(This wont execute)