Beginners · 6 minute read
10 Mistakes Every Java Beginner Makes (and How to Fix Them)
By Java Practice Lab · Published 2026-02-18
Every Java beginner makes the same 10 mistakes. Catching them early saves you weeks of confusion.
1. Comparing Strings with ==
Use .equals(). The == operator compares references, not characters.
2. Forgetting public static void main(String[] args)
The signature is exact. One typo and the JVM won't find your entry point.
3. Mixing up int and Integer
int is a primitive (default 0). Integer is an object (can be null → NullPointerException).
4. Modifying a list while iterating it
Causes ConcurrentModificationException. Use Iterator.remove() or stream filter().
5. Not closing resources
Always use try-with-resources for files, streams, and connections.
6. Catching Exception (or worse, Throwable)
Catch the specific exception you can handle. Swallowing all exceptions hides real bugs.
7. Using raw types like List instead of List<String>
Generics exist for a reason. Always parameterize your collections.
8. Ignoring the difference between checked and unchecked exceptions
Checked = compiler forces you to handle. Unchecked = runtime errors (NullPointerException, IllegalArgumentException).
9. Writing everything in main()
Break code into methods and classes. Aim for methods under 20 lines.
10. Skipping practice
Reading books won't make you fluent. Solve problems daily, even if just one.
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