IT - Selection Statements

IF Statements

Example :If (radius >= 0)
{
 area = radius * radius * PI;
 System.out.println(“The area for the circle of radius “+ radius
 + “ is “ + area);
}

* When radius is bigger than 0 (>= 0) then the statement inside the block is executed.
* Statements which are going to be executed are marked with curly brackets. ( { … } ).
* Blocks aren’t needed when only one statement after “If”.

Example :
int number = Integer.parseInt(intString);
if (number % 2 == 0)
 System.out.println(number + “ is even.”);
If (number % 2 != 0)
 System.out.println(number + “ is odd.”);

If-else Statements

* “If” statement executes only one block when its condition is true.
* If-else statement is needed when executing blocks for both values (True or False).

Example:if (radius >= 0)
{
 area = radius * radius * PI;
 System.out.println(“The area for the circle of radius “ + radius +
 “ is “ + area;
}
else
{
 System.out.println(“Negative input”);
}

* If radius >= 0 is true then area is going to be calculated.
If false then “Negative Input” is going to be appear into console.

* Curly block in “else” can be deleted because it has only 1 statement.

Example :if (number % 2 == 0)
{
 System.out.println(number + “ is even. “);
}
else
{
 System.out.println(number + “ is odd. “);
}

* It is more efficient to write “number % 2 == 0” as “if” parameter’s because it is executed only once a time.

Switch-case statement

 * “if” or “if-else” executes the block by its condition which are true or false.
* Switch-case executes block by its status.
* Switch-case is easier to understand than nested-if and usually be used for multiple-conditions.

* Switch-expression has to be in char, byte, short, or int and put inside parentheses (…).
* Value1, … , to valueN has to be in a same data type as Switch-expression
and can not be in mathematic expression like 1+x.
* If case is found then execution is started from the beginning of the statements
inside the case to the break statement.

* Break is optional in Switch-case statement.
* Default case is optional and it should be executed when no one of the cases apply . 
* Cases are checked sequentially.
* Cases should be listed and default is placed at the last of it.
* Switch-case without break will execute the next case after the case.