[java] What does a "Cannot find symbol" or "Cannot resolve symbol" error mean?

Please explain the following about "Cannot find symbol", "Cannot resolve symbol" or "Symbol not found" errors:

• What do they mean?
• What things can cause them?
• How does the programmer go about fixing them?

This question is designed to seed a comprehensive Q&A about these common compilation errors in Java.

There can be various scenarios as people have mentioned above. A couple of things which have helped me resolve this.

1. If you are using IntelliJ

   File -> 'Invalidate Caches/Restart'

OR

2. The class being referenced was in another project and that dependency was not added to the Gradle build file of my project. So I added the dependency using

   compile project(':anotherProject')

and it worked. HTH!

If eclipse Java build path is mapped to 7, 8 and in Project pom.xml Maven properties java.version is mentioned higher Java version(9,10,11, etc..,) than 7,8 you need to update in pom.xml file.

In Eclipse if Java is mapped to Java version 11 and in pom.xml it is mapped to Java version 8. Update Eclipse support to Java 11 by go through below steps in eclipse IDE Help -> Install New Software ->

Paste following link http://download.eclipse.org/eclipse/updates/4.9-P-builds at Work With

or

Add (Popup window will open) ->

Name: Java 11 support Location: http://download.eclipse.org/eclipse/updates/4.9-P-builds

then update Java version in Maven properties of pom.xml file as below

<java.version>11</java.version>
<maven.compiler.source>${java.version}</maven.compiler.source>
<maven.compiler.target>${java.version}</maven.compiler.target>

Finally do right click on project Debug as -> Maven clean, Maven build steps

"Can not find " means that , compiler who can't find appropriate variable, method ,class etc...if you got that error massage , first of all you want to find code line where get error massage..And then you will able to find which variable , method or class have not define before using it.After confirmation initialize that variable ,method or class can be used for later require...Consider the following example.

I'll create a demo class and print a name...

class demo{ 
      public static void main(String a[]){
             System.out.print(name);
      }
}

Now look at the result..

That error says, "variable name can not find"..Defining and initializing value for 'name' variable can be abolished that error..Actually like this,

class demo{ 
      public static void main(String a[]){

             String name="smith";

             System.out.print(name);
      }
}

Now look at the new output...

Ok Successfully solved that error..At the same time , if you could get "can not find method " or "can not find class" something , At first,define a class or method and after use that..

If you're getting this error in the build somewhere else, while your IDE says everything is perfectly fine, then check that you are using the same Java versions in both places.

For example, Java 7 and Java 8 have different APIs, so calling a non-existent API in an older Java version would cause this error.

One way to get this error in Eclipse :

1. Define a class A in src/test/java.
2. Define another class B in src/main/java that uses class A.

Result : Eclipse will compile the code, but maven will give "Cannot find symbol".

Underlying cause : Eclipse is using a combined build path for the main and test trees. Unfortunately, it does not support using different build paths for different parts of an Eclipse project, which is what Maven requires.

Solution :

1. Don't define your dependencies that way; i.e. don't make this mistake.
2. Regularly build your codebase using Maven so that you pick up this mistake early. One way to do that is to use a CI server.

In my case - I had to perform below operations:

1. Move context.xml file from src/java/package to the resource directory (IntelliJ IDE)
2. Clean target directory.

I solved this error like this... The craziness of android. I had the package name as Adapter and the I refactor the name to adapter with an "a" instead of "A" and solved the error.

You'll also get this error if you forget a new:

String s = String();

versus

String s = new String();

because the call without the new keyword will try and look for a (local) method called String without arguments - and that method signature is likely not defined.

you compiled your code using maven compile and then used maven test to run it worked fine. Now if you changed something in your code and then without compiling you are running it, you will get this error.

Solution: Again compile it and then run test. For me it worked this way.

I too was getting this error. (for which I googled and I was directed to this page)

Problem: I was calling a static method defined in the class of a project A from a class defined in another project B. I was getting the following error:

error: cannot find symbol

Solution: I resolved this by first building the project where the method is defined then the project where the method was being called from.

SOLVED

Using IntelliJ

Select Build->Rebuild Project will solve it

We got the error in a Java project that is set up as a Gradle multi-project build. It turned out that one of the sub-projects was missing the Gradle Java Library plugin. This prevented the sub-project's class files from being visible to other projects in the build.

After adding the Java library plugin to the sub-project's build.gradle in the following way, the error went away:

plugins {
    ...
    id 'java-library'
}

For hints, look closer at the class name name that throws an error and the line number, example: Compilation failure [ERROR] \applications\xxxxx.java:[44,30] error: cannot find symbol

One other cause is unsupported method of for java version say jdk7 vs 8. Check your %JAVA_HOME%

One more example of 'Variable is out of scope'

As I've seen that kind of questions a few times already, maybe one more example to what's illegal even if it might feel okay.

Consider this code:

if(somethingIsTrue()) {
  String message = "Everything is fine";
} else {
  String message = "We have an error";
}
System.out.println(message);

That's invalid code. Because neither of the variables named message is visible outside of their respective scope - which would be the surrounding brackets {} in this case.

You might say: "But a variable named message is defined either way - so message is defined after the if".

But you'd be wrong.

Java has no free() or delete operators, so it has to rely on tracking variable scope to find out when variables are no longer used (together with references to these variables of cause).

It's especially bad if you thought you did something good. I've seen this kind of error after "optimizing" code like this:

if(somethingIsTrue()) {
  String message = "Everything is fine";
  System.out.println(message);
} else {
  String message = "We have an error";
  System.out.println(message);
}

"Oh, there's duplicated code, let's pull that common line out" -> and there it it.

The most common way to deal with this kind of scope-trouble would be to pre-assign the else-values to the variable names in the outside scope and then reassign in if:

String message = "We have an error";
if(somethingIsTrue()) {
  message = "Everything is fine";
} 
System.out.println(message);