It might be that we want to execute a particular statement or block of statements only when the condition is false.

1
The if-else Statement

• It might be that we want to execute a particular
  statement or block of statements only when the
  condition is false.
• The if-else combination provides a choice between
  two options.
• The general logic of the if-else is shown in the
  Figure 1.

2
no
condition is true?
if(condition) //statements //when
condition //is true else
//statements //when condition //is
false next statement
yes
Statement or Block of Statements for true
Statement or Block of Statements for false
Next Statement
Figure 1. One of the two blocks in an if-else
statement is always executed.
3

• Often you'd want to execute a statement if a
  certain condition is met, and a different
  statement if the condition is not met. This is
  what else is for. else extends an if statement to
  execute a statement in case the expression in the
  if statement evaluates to FALSE.

4
package ifelsestatement public class Main
public static void main(String args)
throws java.io.IOException char
ch, answer'K' System.out.println("I am
thinking of a letter between A and Z.")
System.out.print("Can you gess it ")
ch(char)System.in.read()
if(chanswer) System.out.println("
RIGHT") else
System.out.println("Sorry, you did not guess
it!")
5
run I am thinking of a letter between A and
Z. Can you gess it T Sorry, you did not guess
it! BUILD SUCCESSFUL (total time 10 seconds)
6

• It is also possible to nest if-else statements
  within ifs, ifs within if-else statements, and
  indeed if-else statements within other if-else
  statements.
• This provides us with plenty of versatility and
  considerable room for confusion.
• Next an example of an if-else nested within an if

7

• if(coffeey)
• if(donutsy)
• System.out.println(We have coffee and
  donuts.)
• else
• System.out.println(We have coffee, but not
  donuts.)

8

• An example of an if nested within an if-else
• if(coffeey)
• if(donutsy)
• System.out.println(We have coffee and
  donuts.)
• else if(teay)
• System.out.println(We have no coffee, but we
  have tea.)

9

• else if, as its name suggests, is a combination
  of if and else. Like else, it extends an if
  statement to execute a different statement in
  case the original if expression evaluates to
  FALSE. However, unlike else, it will execute that
  alternative expression only if the else if
  conditional expression evaluates to TRUE. For
  example, the following code would display a is
  bigger than b, a equal to b or a is smaller than
  b

10
package elseifstatement public class Main
public static void main(String args)
int a5, b5 if(agtb)
System.out.println("a is bigger than b.")
else if(ab) System.out.println("a
is equal to b.") else
System.out.println("b is bigger than a.")
run a is equal to b. BUILD SUCCESSFUL (total
time 1 second)
11

• There may be several else ifs within the same if
  statement. The first else if expression (if any)
  that evaluates to TRUE would be executed.
• The else if statement is only executed if the
  preceding if expression and any preceding else if
  expressions evaluated to FALSE, and the current
  else if expression evaluated to TRUE.