java.lang.IllegalArgumentException

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Java

java.lang.IllegalArgumentException

A method was passed an argument that is invalid or out of its accepted range.

What it means

A method was passed an argument that is invalid or out of its accepted range.

Likely cause

Null, empty, out-of-range, or otherwise malformed values passed where the method's contract forbids them.

How to fix it

Validate arguments before the call and read the method's preconditions. Add your own checks (Objects.requireNonNull, range checks) at API boundaries to fail early with clear messages.

Other Java errors

java.lang.NullPointerException Code dereferenced a variable that was null, calling a method or accessing a field on nothing. java.lang.ClassNotFoundException The JVM could not find a class by name when loading it at runtime. java.lang.NoClassDefFoundError A class that was available at compile time could not be loaded at runtime. java.lang.OutOfMemoryError: Java heap space The JVM exhausted its heap and could not allocate more objects. java.lang.ArrayIndexOutOfBoundsException Code accessed an array element at an index outside the array's valid range. java.lang.StringIndexOutOfBoundsException A string operation used a character index outside the string's bounds. java.lang.NumberFormatException A string could not be parsed into a numeric type. java.lang.ClassCastException An object was cast to a type it is not an instance of. java.util.ConcurrentModificationException A collection was structurally modified while it was being iterated. java.lang.StackOverflowError The call stack exceeded its size limit, almost always from unbounded recursion. UnsupportedClassVersionError A class was compiled for a newer Java version than the JVM running it. java.lang.IllegalStateException A method was called while the object was in a state that does not allow it. java.lang.ArithmeticException: / by zero An integer arithmetic operation attempted to divide by zero. java.lang.NoSuchMethodError The JVM could not find a method that existed at compile time. Error: Could not find or load main class The java launcher could not locate or load the specified main class.

About Error Code Lookup

The Error Code Lookup is a searchable directory of more than 200 common error messages and codes across 12 categories: HTTP status codes, Windows error codes, browser and network errors, JavaScript, Python, PHP, Node.js and npm, Java, MySQL, Git, Linux shell errors and email/SMTP codes. Every entry is written in plain language for quick troubleshooting.

Each error is explained in three parts: what the message actually means, what usually causes it and concrete steps to fix it. That structure turns a cryptic string like ERR_CONNECTION_REFUSED or 0x80070005 into an actionable checklist instead of a guessing game.

You can filter the list by category, search by code, constant or message fragment, and copy any code with one click. Every error also has its own dedicated page with related errors from the same category, so you can bookmark or share a direct link to the exact fix.

How to use Error Code Lookup

  1. Type the error code or message into the search box — for example 404, ERR_NAME_NOT_RESOLVED or 0x80070005.
  2. Narrow the results with the category filter (HTTP, Windows, JavaScript, MySQL and so on) if the search returns too many entries.
  3. Open the matching entry to read what it means, its likely cause and how to fix it.
  4. Use the copy button to grab the exact code for a bug report or support ticket.
  5. Check the related errors section for other errors from the same category.

Frequently asked questions

It covers 12 categories: HTTP status codes, Windows system errors, browser and network errors, JavaScript, Python, PHP, Node.js and npm, Java, MySQL, Git, Linux shell errors and email/SMTP reply codes — more than 200 entries in total.

Search with fewer words. The shortest unique part works best: just the numeric code (“404”, “0x80070005”) or the constant name (“ERR_NAME_NOT_RESOLVED”) rather than the full sentence your system printed.

Yes. Each entry has a dedicated detail page explaining the meaning, likely cause and fix, plus related errors from the same category. You can bookmark it or send the link directly to a colleague or a support ticket.

The fixes describe the standard, widely accepted resolution for each error. Still, read the likely-cause section first — the same code can have several triggers, and matching the cause to your situation tells you which fix applies.

Yes, it is completely free. You can search, browse the category directory and open as many error detail pages as you need without an account.
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