CS121/IS223
Conditional Statements
In a program, we frequently have to make choices. Given some condition, we can have the
program do one thing or another. Programming languages have if – else statements that do this.
We will look at the one for Java.
The form for the conditional in Java is
if (some condition is true)
do something
else
do something else
An example of this is a statement that decides which of two numbers is larger.
int age1 = 3, age2 = 6;
if (age1 > age2)
System.out.println ("The first animal is older.");
else
System.out.println ("The second animal is older.");
In the case above, the second age is greater, so the second statement will be displayed.
Sometimes we want to do several things if a condition is true. In that case, we have to enclose
the statements in curly braces. The if – else statement only does one thing otherwise.
if (age1 >= age2)
{
System.out.print ("The first animal is older");
System.out.println (" or the animals are the same age.");
}
else
{
System.out.println ("The second animal is older.");
}
The curly braces were not needed in the else part (called a clause), but putting them in does not
hurt.
We can also have if – else statements inside of if – else statements.
if (age1 > age2)
System.out.println ("The first animal is older.");
else
if (age1 == age2)
System.out.println ("The animals are the same age.");
else
System.out.println ("The second animal is older.");
The computer will execute the first correct condition and not test the remaining ones.
A different example has an entire cascade of if – else statements.
// Method to analyze a patient's temperature.
public void classifyTemperature ()
{
System.out.print ( "Enter your temperature. ");
temp = scan.nextInt ();
