A syntax error is a mistake in the structure or grammar of code (like a missing semicolon or unmatched brace) that violates the rules of the programming language, so the compiler catches it and the program never runs.
A syntax error happens when your code breaks Java's grammar rules. Think of it like a sentence with no period or a word spelled wrong in a language that refuses to guess what you meant. Java's compiler reads your code before anything runs, and if the structure is wrong, it stops and reports the error. Classic examples include a missing semicolon (int x = 5 int y = 10;), unmatched curly braces or parentheses, misspelled keywords (Strng instead of String), and wrong capitalization (system.out.println instead of System.out.println).
The defining feature of a syntax error is when it gets caught. The compiler finds it at compile time, before your program ever executes. That makes syntax errors the easiest of the three error types to find and fix, because the compiler literally points at the line and complains. Compare that to runtime errors (the program compiles but crashes while running) and logic errors (the program runs fine but produces wrong answers).
Error types show up at the very start of AP Computer Science A, in Unit 1, where the CED expects you to understand how Java code gets compiled and run. From there, the syntax/runtime/logic distinction follows you through every unit, because every program you write or read on the exam can fail in one of these three ways. The exam loves asking you to classify an error, and the trick is always the same. Ask yourself when the error gets caught. If the compiler refuses to even run the code, it's a syntax error. If the code compiles but crashes mid-run (like dividing by zero), it's a runtime error. If it runs to completion but gives a wrong answer, it's a logic error. Knowing this taxonomy cold also makes you a faster debugger on the FRQs, where you're writing Java by hand with no compiler to bail you out.
Keep studying AP Computer Science A Unit 1
Compiler (Unit 1)
The compiler is the gatekeeper that catches syntax errors. It translates your Java source code into something runnable, and if your code breaks Java's grammar, translation fails and you get an error message instead of a program. No compiler, no syntax error detection.
Runtime Error (Unit 1)
A runtime error sneaks past the compiler because the code is grammatically perfect, then crashes during execution. Dividing by zero is the classic example. The code int x = 10 / 0; compiles fine, but throws an ArithmeticException the moment it runs. Syntax errors never get that far.
Logic Error (Unit 1)
A logic error is the sneakiest of the three. The code compiles, runs, and finishes without crashing, but the answer is wrong, like dividing a sum of five test scores by four. The compiler can check your grammar, but it can't check your math or your intent.
System.out.println() (Unit 1)
Print statements are a goldmine for syntax errors because Java is case-sensitive and picky. Writing system.out.println() with a lowercase s, or forgetting a closing parenthesis or quotation mark, is a syntax error the compiler will flag immediately.
Multiple-choice questions test this term by showing you a snippet of broken code and asking you to classify the error. A statement like int x = 5 int y = 10; with no semicolon between statements is a syntax error. Division by zero that compiles but crashes at runtime is a runtime error (an exception). Code that runs but divides by the wrong number is a logic error. The fastest way to nail these questions is to ask when the error surfaces. Compile time means syntax, crash during execution means runtime, wrong output means logic. On the free-response section, you write Java by hand, and the scoring guidelines focus on whether your logic is correct, but certain syntax mistakes can still cost penalty points. Clean, correct syntax in your FRQ answers (semicolons, matched braces, correct capitalization) is free insurance.
Both stop your program from working, but they fail at different stages. A syntax error is caught by the compiler before the program ever runs, so the code never executes at all. A runtime error means the code compiled successfully and started running, then crashed mid-execution, like a division by zero throwing an ArithmeticException. Quick test: if there's an error message before the program runs, it's syntax; if the program starts and then dies, it's runtime. (And if it runs to the end but the answer is wrong, that's a logic error, the third member of the family.)
A syntax error breaks the grammar rules of Java, so the compiler catches it at compile time and the program never runs.
Common syntax errors include missing semicolons, unmatched braces or parentheses, misspelled keywords, and wrong capitalization like lowercase 'system' in System.out.println().
The three AP CSA error types are sorted by when they appear: syntax errors at compile time, runtime errors during execution, and logic errors in the output.
Division by zero is NOT a syntax error; it compiles fine and crashes at runtime as an ArithmeticException.
Code that runs without crashing but produces a wrong answer has a logic error, not a syntax error, because the compiler only checks structure, not intent.
A syntax error is a mistake in the structure or grammar of your code that violates Java's language rules, like a missing semicolon or unmatched brace. The compiler catches it before the program runs, so the code never executes.
No. Code like int x = 10 / 0; follows Java's grammar perfectly, so it compiles without complaint. It crashes when that line executes, throwing an ArithmeticException, which makes it a runtime error.
A syntax error stops the compiler, so the program never runs. A logic error compiles and runs without crashing but gives a wrong result, like dividing the sum of five test scores by four. The compiler checks your grammar, not your math.
Possibly, but the scoring focuses mostly on your logic. The College Board's scoring guidelines apply small penalties for certain syntax mistakes, so a stray missing semicolon usually won't sink you, but sloppy structure like unmatched braces can. Write clean code and you don't have to worry about it.
Missing semicolons between statements (like int x = 5 int y = 10;), unmatched curly braces or parentheses, misspelled keywords, missing quotation marks around strings, and case mistakes like writing system.out.println() instead of System.out.println().
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.