How to Fix Common Minecraft Java Errors

By PickaxeKit Editorial Team · Updated 2026-11-08

Most Java errors mean the wrong Java version or a wrong file path. Minecraft 26.3 needs Java 25; install it, then run the server with that Java.

UnsupportedClassVersionError

This means your Java is older than the Minecraft version needs. The error shows a class file version number. Match it to Java with this table, then install that Java from the Java guide.

'java' is not recognized as a command

Java is installed but not on your PATH, or not installed at all. Reinstall Java and tick the option to add it to PATH, then open a new terminal. Or run Java with its full path.

• The file name in your command does not match the real file (for example server.jar vs minecraft_server.jar).
• The terminal is in a different folder. Open it inside the server folder, or use the full path to the jar.
• Windows hides file extensions, so the file may really be server.jar.jar. Turn on file name extensions to check.

Could not reserve enough space for object heap

The -Xmx value asks for more memory than Java can get. Lower it (for example -Xmx2G), and make sure you installed 64-bit Java: 32-bit Java can only use a small amount of memory.

Which Java goes with which Minecraft