You've already learned about several binary
operators in Java: +, -, *, /, and %, for example. Binary operators
have 2 operands (a value on the left of the operator and a value
on the right of the operator). Unary operators such as ++ and --
have a single operand. The ternary operator ?:
has 3 operands: operand1 ? operand2 : operand3
The ternary operator, also called the conditional operator,
allows you to write a single expression that evaluates a
relational expression and returns one result if the expression
is true, and a different result if the expression is false.
It's a helpful operator to use when you want to get a value
based on a specific condition.
Once you know how to use relational expressions, you can use the
conditional operator.
The conditional operator allows you to code a simple decision that can
result in one of two actions. For example, with a conditional operator
you can check the value of a variable to see if it's larger than 100.
If it is, you can display a message on the console. If it isn't, you
can display a different message.
The conditional operator is the ? symbol. It's actually
a ternary operator - it requires three operands (binary operators
require 2 operands, unary operators require 1 operand). The
general format of the conditional is as follows:
The conditionalExpression is an expression that evaluates to
a boolean value of true or false.
A typical conditional expression
uses one of the binary relational operators (<, <=, >,
>=, == (equals), != (not equals)) with an operand on either side.
For example, assume x=10, y=5, and z=20:
x > y - evaluates to true z >= 20 - evaluates to true x * y < z - evaluates to false x + y >= z - evaluates to false
Keep in mind that the conditional expression must appear in
parentheses and it must always have a boolean (true or false)
result.
The valueIfTrue is the value that the operator returns
if the conditional expression evaluates to true, and the
valueIfFalse is the value that the operator returns
if the conditional expression evaluates to false. Remember,
this is an operator, so like any other operator (*, +, <)
there is a result. With a conditional operator, the 2nd and
3rd operands are the two possible results that this operator
could return. Examples (assume z = 50):
(x * x >= 0) ? 10 : 20 // returns the integer value 10
(z >= 20) ? "yes" : "no" // returns the string "yes"
(z < 20) ? 10.5 : 25.0 // returns the double value 25.0
Like any other expression, a conditional expression returns a value,
so you must make sure
that you are using the expression's result, or storing it
somewhere. If you are putting the return value in a variable,
you must make sure that the variable's data type matches the
type of the 2nd and 3rd operands. For example:
1. The method Math.random() generates a random double
number greater than 0.0 and less than 1.0. Write a program
that simulates flipping a coin. Call the Math.random() method
and if the number generated is less than .5, display
"HEADS". Otherwise, display "TAILS".
2. To generate a random integer value, you have to modify
the result returned by Math.random(). For example, to generate
a random number between 1 and 10, you would do this:
double randomNum = Math.random(); // gets a random double
randomNum *= 10; // moves the decimal over 1 spot
int randomInt = (int)randomNum; // chops off the decimal part
// now we have a number from 0 to 9, so add 1 to make it 1 to 10
randomInt++;
Of course, most people find it easier to simply do this:
int randomNum = (int)(Math.random() * 10) + 1;
Write a program that generates a random integer from 1 to 5. Then
ask the user to guess that number. If they guess correctly, display
the message, "You guessed correctly!". If they guess incorrectly,
display the message, "Sorry, you guessed incorrectly.".
3. Write a program that simulates the tossing of two dice
(generate two random integers from 1 to 6). If doubles are rolled,
display a "You Win!!" message. Otherwise, tell the user what dice
values they rolled.
4. Second Life's breedable KittyCatS!™ can breed out kittens
when they're under 121 days in age. Kittens can't breed, so a cat can't breed
out kittens until it's 14 days old. Write a program that prompts the user
for the age of the cat in days and displays either "Breedable: ON" (if the
cat is of breedable age) or "Breedable: OFF" (if the cat is not of breedable
age.
5. A program prompts the user to enter a department number. A
valid department number is:
between 1 and 45
between 50 and 60
department 100
Display whether a user-entered department number is "valid" or "invalid".
Use a single conditional statement.
