';' expected
What causes it
A missing semicolon.
The fix
Add ; at the end of the statement. Check the line above too — javac points at the line after the missing one.
Week 1Meet it in the bestiary
Error cheat sheet
Paste what you saw, or search a word from it. Red text is feedback, not failure — every one of these has happened to everyone on your team.
Before you search
Read the first error, go to that line number, and check the line above it too. Later errors are usually the first one echoing.12 of 12 shown
cannot find symbol
What causes it
A typo, a missing import, or a variable that was never declared.
The fix
Read the
symbol:line — that is the exact name javac could not find. Check spelling and capitals, then use Quick Fix to add the import.What it looks like cannot find symbol symbol: variable motorSped location: class MainWeek 1Meet it in the bestiaryincompatible types
What causes it
A value of one type assigned to a variable of another.
The fix
Match the types.
"0.5"is text;0.5is a number.5 / 2is2because both are ints — write5.0 / 2.What it looks like incompatible types: java.lang.String cannot be converted to doubleWeek 1Meet it in the bestiarymissing return statement
What causes it
A method that promises a value has a path that returns nothing.
The fix
Every route through the method needs a
return, including the one after the lastif.Week 2Meet it in the bestiaryreached end of file while parsing
What causes it
A missing closing brace.
The fix
Count your braces, or auto-format the file (Shift+Alt+F) — badly indented code is where the missing
}shows itself.Week 2Meet it in the bestiaryclass X is public, should be declared in a file named X.java
What causes it
The class name and the file name do not match.
The fix
Rename one to match the other. Java is case sensitive:
intake.javais notIntake.java.What it looks like class Main is public, should be declared in a file named Main.javaWeek 3Meet it in the bestiarynon-static method cannot be referenced from a static context
What causes it
A method that belongs to an object was called on the class itself.
The fix
Make an object first:
Intake intake = new Intake();thenintake.run();. Or mark the methodstaticif it does not need an object.What it looks like non-static method clamp(double,double,double) cannot be referenced from a static contextWeek 3Meet it in the bestiaryNullPointerException
What causes it
Using an object that was never created.
The fix
Find the variable named in the message and check it was given a value with
new. This one happens while the code runs, not while it compiles.What it looks like Exception in thread "main" java.lang.NullPointerExceptionWeek 3Meet it in the bestiarySimulation will not start
What causes it
A build error, or the firewall blocking it.
The fix
Read the terminal — the first red line is the real problem. If Windows asks about the firewall, allow it on private networks.
Week 4No Robot Code
What causes it
The code crashed while starting up on the robot.
The fix
Open the Driver Station console and read the stack trace. It is almost always a NullPointerException in the constructor.
Week 7Deploy cannot find the robot
What causes it
Wrong team number in project settings, or not connected to the robot.
The fix
Check the team number in the WPILib project settings, then check the radio connection and that the Driver Station shows communications.
Week 7Vendor import not found
What causes it
The vendor library is not installed in this project.
The fix
Ctrl+Shift+P, then WPILib: Manage Vendor Libraries, then install the REV or CTRE library online.
What it looks like package com.revrobotics does not existWeek 7Meet it in the bestiary