APCSA Question of the Week: Primitive Types 1

Week 2: Primitive Types 1

This week's question is from Unit 1: Primitive Types. Out of the 40 multiple-choice questions (MCQs) you'll see on the exam, only 1-2 questions will be on Primitive Types.

These should be easy points — yet only 14% of students have gotten this correct on Passionfruit.

Here's the link to the question!

Try it for yourself before scrolling to see the answer and explanation below!

Explanation and Solution

As always, let's first talk about what concepts are at play:

1. Integer Division vs. Floating-Point Division

In Java, when you divide two integers, the result is always an integer - any decimal portion is truncated. This is called integer division. For example:

• 1/2 equals 0 (not 0.5)

• 5/2 equals 2 (not 2.5)

However, if either operand is a floating-point number (like a double), Java performs floating-point division, which preserves the decimal portion:

• 1.0/2 equals 0.5

• 1/2.0 equals 0.5

2. Type Casting

Type casting is Java's way of converting one data type to another. When casting to a wider type (like int to double), Java performs the conversion automatically. But the placement of the cast is crucial - it only affects what's immediately next to it or within its parentheses.

3. Operator Precedence

Java follows specific rules about which operations happen first:

1. Operations in parentheses

2. Type casts

3. Multiplication and division

4. Addition and subtraction

Now let's apply these concepts:

Which of these expressions evaluate to 0.5?

I. (double)(1/2)

II. (double)1/2

III. 1/(double)2

Let's evaluate each expression:

Expression I: (double)(1/2)

1. Inside parentheses first: 1/2 is integer division = 0

2. Cast to double: (double)0 = 0.0

Result: 0.0 (not 0.5)

Expression II: (double)1/2

1. Cast happens first: (double)1 = 1.0

2. Division: 1.0/2 = 0.5 (floating-point division)

Result: 0.5

Expression III: 1/(double)2

1. Cast happens first: (double)2 = 2.0

2. Division: 1/2.0 = 0.5 (floating-point division)

Result: 0.5

The Answer:

Only expressions II and III (answer option E) evaluate to 0.5.

Key Takeaways and Tips

The key lesson is that to get accurate decimal division, you need to ensure at least one operand is a floating-point number BEFORE the division occurs.

Common pitfall: Many students assume `(double)(1/2)` will give them 0.5, but by then it's too late - the integer division has already happened!

If you have any additional questions, feel free to ask Passionfruit's AI Tutor or email us at jason@passionfruitlearning.com.

See you next time!