Real-Life Examples
This example shows how you can use if..else to "open a door" if the user enters the correct code:
Example
int doorCode = 1337;
if (doorCode == 1337) {
System.out.println("Correct code. The door is now open.");
} else {
System.out.println("Wrong code. The door remains closed.");
}
This example shows how you can use if..else to find out if a number is positive or negative:
Example
int myNum = 10; // Is this a positive or negative number?
if (myNum > 0) {
System.out.println("The value is a positive number.");
} else if (myNum < 0) {
System.out.println("The value is a negative number.");
} else {
System.out.println("The value is 0.");
}
Find out if a person is old enough to vote:
Example
int myAge = 25;
int votingAge = 18;
if (myAge >= votingAge) {
System.out.println("Old enough to vote!");
} else {
System.out.println("Not old enough to vote.");
}
Find out if a person is old enough to vote, and if they are a citizen (using nested if statements):
Example
int age = 20;
boolean isCitizen = true;
if (age >= 18) {
System.out.println("Old enough to vote.");
if (isCitizen) {
System.out.println("And you are a citizen, so you can vote!");
} else {
System.out.println("But you must be a citizen to vote.");
}
} else {
System.out.println("Not old enough to vote.");
}
Find out if a number is even or odd:
Example
int myNum = 5;
if (myNum % 2 == 0) {
System.out.println(myNum + " is even");
} else {
System.out.println(myNum + " is odd");
}
Check temperature:
Example
int temperature = 30;
if (temperature < 0) {
System.out.println("It's freezing!");
} else if (temperature < 20) {
System.out.println("It's cool.");
} else {
System.out.println("It's warm.");
}
System access control example - You must be logged in, and then you either need to be an admin, or have a high security clearance (level 1 or 2) to get access:
Example
boolean isLoggedIn = true;
boolean isAdmin = false;
int securityLevel = 3; // 1 = highest
if (isLoggedIn && (isAdmin || securityLevel <= 2)) {
System.out.println("Access granted");
} else {
System.out.println("Access denied");
}
// Try changing securityLevel to test different outcomes:
//
// securityLevel 1 = Access granted
// securityLevel 2 = Access granted
// securityLevel 3 = Access denied
// securityLevel 4 = Access denied
//
// If isAdmin = true, access is granted.
