The Purdue CS 180 Test Out

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The Purdue CS 180 Test Out

A few notes:

This guide is intended to build off Kart's Optimizing Purdue CS and go more in depth on how to pass the CS 180 test out if you choose to attempt it.

I took and passed the test out in fall of 2025. The information here is based off that test, so this could become out of date in the future.

Should I do it?

As Kart mentions, they say that it's not recommended, but you should consider doing it if you are already quite experienced in Java. If you are not super experienced in Java, I wouldn't recommend trying to study for it, because the test is quite hard.

Note that you do have to take an additional 300+ level course and an additional course to satisfy the teambuilding and collaboration requirement.

What the test is like

In fall 2025 it was pure multiple choice with 75 questions in 2 hours and a passing threshold of 85%. This does not leave a lot of room for questions you don't know how to solve or mistakes. Most (maybe around 2/3) of the questions are quite straightforward and should be quite easy if you know Java well. The other (around 1/3) questions can be quite difficult, asking about obscure language features or including very sneaky or misleading code. Those questions are, in my opinion, what separates a passing and failing score.

Studying tips

• Be familiar with threads, networking, and GUIs. These are emphasized quite a bit in the test-out but most people aren't familiar with them.
• Read each question very carefully. Some of the code excerpts are quite sneaky.
• Know the more obscure language featues. These include but are not limited to:
  • If you have a switch branch without a break, then execution goes on into the next branch
  • Negative array indices are not allowed
  • length vs size() for arrays vs lists
  • Interfaces vs abstract classes (an interface can't contain an implementation because you're not meant to inherit off one)
  • synchronized keyword
  • Java Swing layouts (border, flow, grid)
  • Exceptions (checked vs unchecked, throws keyword, you can also declare extraneous exceptions in the throws keyword)
  • Bitwise operations
  • Overloading
  • Syntax for array initialization

Practice questions

The past final exams (https://www.cs.purdue.edu/homes/cs180/exams.html) I think represent the questions you'll see on the test out pretty well. Do note that these questions are somewhat harder than the hard questions you'll see on the test out.

Here's also a few more questions (these are written completely on my own) that resemble what I saw on the test:

Easier 1:

Which of these methods will not compile?

void a() throws IOException {
  throw new IOException();
}

void b() {
  throw new IOException();
}

void c() {
  throw new RuntimeException();
}

Answer

Answer: b() fails to compile.

Commentary: This question is very straightforward as long as you understand how exceptions work.

Easier 2:

What will be the output of the following code?

public static void myMethod() {
  int count = 0;
  for (int i = 1; i < 50; i *= 2) {
    count++;
  }
  System.out.println(count);
}

public static void main(String[] args) {
  myMethod();
}

Answer

Answer: 6 - count is incremented for 1, 2, 4, 8, 16, and 32.

Commentary: This question is pretty straightforward as long as you understand what the code is doing.

Harder 1:

What will be the output of the following code?

public static void myMethod() {
  float[] numbers = new float[4];
  for (int i = 0; i < numbers.length; i++) {
    numbers[i] += 0.5 * i;
  }
  System.out.println(numbers[0] + numbers[3]);
}

public static void main(String[] args) {
  myMethod();
} 

Answer

Answer: Fails to compile because numbers[i] is a float while 0.5 * i is a double.

Commentary: The compilation error in this one is very easy to miss if you aren't looking at it closely.

Harder 2:

What will be the output of the following code?

public static void main(String[] args) {
  int total = 0;
  for (int x = 0; x < 7; x += 2) {
      switch (x) {
        case 0: total += 2;
        case 1: total += 4;
        case 2: total += 6; break;
        case 3: total -= 1; break;
        case 4: total *= 2;
        default: total += 1; break;
      }
  }
  System.out.println(total);
}

Answer

Answer: 38 - when x = 0, total increases to 12. When x = 2, total increases to 18. When x = 4, total increases to 37. When x = 6, total increases to 38.

Commentary: This tests your knowledge of weird switch statement behavior.

I second this