Ternary operator in Java - Mini Project: Build & Apply

Using the Ternary Operator in Java

📖 Scenario: You are creating a simple program that decides if a person is an adult or a minor based on their age.

🎯 Goal: Build a Java program that uses the ternary operator to check if a person is an adult (18 or older) or a minor (under 18) and prints the result.

📋 What You'll Learn

Create an integer variable age with the value 20

Create a string variable status that uses the ternary operator to set 'Adult' if age is 18 or more, otherwise 'Minor'

Print the status variable

💡 Why This Matters

🌍 Real World

Deciding between two options quickly based on a condition is common in apps, like showing messages based on user age.

💼 Career

Understanding the ternary operator helps write concise and readable code, a skill useful for any Java developer.

1

Create the age variable

Create an integer variable called age and set it to 20.

Java

# Your code here

Hint

Use int age = 20; inside the main method.

2

Create the status variable using the ternary operator

Create a string variable called status that uses the ternary operator to set it to "Adult" if age is 18 or more, otherwise "Minor".

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        
        // Create status using ternary operator
        // Your code here
    }
}

Hint

Use String status = age >= 18 ? "Adult" : "Minor"; to assign the value.

3

Print the status variable

Write a System.out.println statement to print the value of the status variable.

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        String status = age >= 18 ? "Adult" : "Minor";
        
        // Print the status
        // Your code here
    }
}

Hint

Use System.out.println(status); to show the result.

4

Run the program to see the output

Run the program. It should print Adult because the age is 20.

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        String status = age >= 18 ? "Adult" : "Minor";
        System.out.println(status);
    }
}

// Run the program to see the output

Hint

The program prints Adult because 20 is greater than or equal to 18.

Practice

1. What does the ternary operator condition ? valueIfTrue : valueIfFalse do in Java?

easy

A. It creates a loop that runs twice.

B. It chooses one of two values based on the condition's truth.

C. It declares a new variable.

D. It throws an error if the condition is false.

Solution

1. Step 1: Understand the ternary operator syntax

   The ternary operator uses a condition followed by a question mark, then two values separated by a colon.

2. Step 2: Determine its purpose

   It returns the first value if the condition is true, otherwise the second value.

3. Final Answer:

   It chooses one of two values based on the condition's truth. -> Option B

4. Quick Check:

   condition ? trueValue : falseValue = chooses value [OK]

Hint: Think: condition true? pick first : else pick second [OK]

Common Mistakes:

• Confusing ternary with loops
• Thinking it declares variables
• Assuming it throws errors automatically

2. Which of the following is the correct syntax for a ternary operator in Java?

easy

A. int result = (x > 0) ? (1 : -1);

B. int result = (x > 0) ? 1, -1;

C. int result = (x > 0) : 1 ? -1;

D. int result = (x > 0) ? 1 : -1;

Solution

1. Step 1: Review ternary operator syntax

   The correct syntax is: condition ? valueIfTrue : valueIfFalse;

2. Step 2: Check each option

   int result = (x > 0) ? 1 : -1; matches the correct syntax exactly. Others have wrong punctuation or order.

3. Final Answer:

   int result = (x > 0) ? 1 : -1; -> Option D

4. Quick Check:

   condition ? trueValue : falseValue syntax [OK]

Hint: Remember: question mark then colon separate values [OK]

Common Mistakes:

• Using comma instead of colon
• Swapping question mark and colon
• Adding extra parentheses incorrectly

3. What is the output of this Java code?

int a = 5;
int b = 10;
int max = (a > b) ? a : b;
System.out.println(max);

medium

A. 10

B. false

C. true

D. 5

Solution

1. Step 1: Evaluate the condition (a > b)

   Since a=5 and b=10, 5 > 10 is false.

2. Step 2: Apply ternary operator

   Because condition is false, max gets value b, which is 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   (5 > 10) ? 5 : 10 = 10 [OK]

Hint: Check condition result true or false to pick value [OK]

Common Mistakes:

• Choosing the first value always
• Confusing variable values
• Expecting boolean output

4. Identify the error in this code snippet:

int x = 10;
int y = 20;
int min = x > y ? x, y;
System.out.println(min);

medium

A. Missing colon ':' in ternary operator

B. Incorrect variable declaration

C. Using comma instead of semicolon

D. No error, code runs fine

Solution

1. Step 1: Check ternary operator syntax

   The ternary operator requires a colon ':' between true and false values.

2. Step 2: Identify the error in code

   The code uses a comma ',' instead of a colon ':', causing a syntax error.

3. Final Answer:

   Missing colon ':' in ternary operator -> Option A

4. Quick Check:

   condition ? valueIfTrue : valueIfFalse needs ':' [OK]

Hint: Ternary needs '?' then ':'; commas cause errors [OK]

Common Mistakes:

• Using comma instead of colon
• Forgetting colon entirely
• Misplacing semicolons inside ternary

5. Given this code, what is the value of result?

int score = 75;
String result = (score >= 90) ? "A" : (score >= 80) ? "B" : (score >= 70) ? "C" : "F";
System.out.println(result);

hard

A. "A"

B. "B"

C. "C"

D. "F"

Solution

1. Step 1: Evaluate nested ternary conditions in order

   score=75. Check if score >= 90? No. Then check if score >= 80? No. Then check if score >= 70? Yes.

2. Step 2: Assign value based on first true condition

   Since score >= 70 is true, result is assigned "C".

3. Final Answer:

   "C" -> Option C

4. Quick Check:

   Nested ternary picks first true condition value [OK]

Hint: Read nested ternary top to bottom, pick first true [OK]

Common Mistakes:

• Stopping at first false condition
• Ignoring nested ternary order
• Confusing string quotes