Error cannot find symbol scanner

The “Cannot find symbol” Compilation Error

Table of Contents

Symbols and Symbol Table

Before diving into the details of the “cannot find a symbol” error, here is a brief introduction to symbols and symbol tables in Java. A symbol refers to an identifier in the compilation process in Java. All the identifiers used in the source code are collected into a symbol table in the lexical analysis stage. The symbol table is a very significant data structure created and maintained by the compilers to store all the identifiers and their information.

This information is entered into the symbol tables during lexical and syntax analysis which is then used in multiple phases of compilation.

From classes, variables, interfaces to methods, all of them require an identifier for declaration. During the code generation process, when these identifiers are encountered in the source code, the compiler checks for them in the symbol tables and the stored information is then used to verify the declarations, the scope of a variable, and verifying that the expression is semantically correct or not.

The compilation process usually does not go as smooth as you would think. Errors are inevitable in any development stage and one of the very commonly occurring errors during the compilation process is Java “cannot Find Symbol” Error. In this article, we will be discussing the reasons behind the occurrence of Java cannot find symbol errors and how you can resolve them.

Cannot Find Symbol Error

As the name suggests, the Java cannot find symbol error occurs when a required symbol cannot be found in the symbol table. Although there can be various reasons behind this, it points to one fact the Java compiler was unable to find the symbol and its details associated with a given identifier.

As there are a variety of Java compilers available, many of them use slightly different terminologies, because of that, you can also find the “cannot find symbol” error termed as the “symbol not found” or “cannot resolve symbol” error. Besides the name, there is simply no difference between these errors.

Structure of Java Cannot Find Symbol Error

The compiler output a specific error message with the cannot find symbol error.

It contains the following two fields that indicate the missing symbol and its location:

1. Symbol: The name and type of the identifier you are looking for.
2. Location: The particular class in which that identifier has been referenced.

Causes of Java Cannot Find Symbol Error

We will be discussing the following most common causes of the cannot find symbol error during compilation,

• misspelt identifiers
• Undeclared variables
• Out of scope references to variables and methods
• The unintentional omission of import statements

Misspelt identifier names

This is the most common and most occurring reason behind the Java cannot find symbol error. Misspelling an existing variable, class, interface, package name or a method causes the “cannot find symbol error” as the compiler cannot recognize the symbol and identifies it as an undeclared variable. Java identifiers are also case-sensitive, so even a slight variation of an existing variable will result in this error.

See code example below:

It can be easily resolved by correcting the spelling of the function in line 9.

Undeclared variables

When the Java compiler come across an identifier used in the code but it cannot be found in the symbol table, the “cannot find symbol” error is shown. The only reason behind the absence of a variable from the symbol table is that it is not declared in the code. Some new programming languages do not require explicit declaration of variables but it is mandatory in Java to always declare a variable before it is used or referenced in the source code.

The code snippet below demonstrates an undeclared variable in the code. In this case, the identifier sum on line 7, causes the Java “cannot find symbol error”.

See code example below:

Declaring this variable by specifying the appropriate data type can easily resolve the error.

See this corrected code below,

Out of scope variable

When a Java code attempts to access a variable declared out of scope such as in a non-inherited scope the compiler will result in issuing the “cannot find symbol” error. This commonly happens when you attempt to access a variable declared inside a method or a loop, from outside of the method.

See this code example below where the “cannot find symbol” error has occurred when the counter variable which is declared inside a for loop is attempted to be accessed from out of the loop.

See code below:

I can be easily resolved by just moving the if block inside the for loop (local scope).

See this code example,

Missing import statement

Java allows you to use built-in classes or any imported libraries in your code to save your time by reusing the code but it requires importing them properly using the import statements at the start. Missing the import statement in your code will result in the cannot find symbol error.

java.util.Math class is utilized in the code given below but it is not declared with the “import” keyword, resulting in the “cannot find symbol error”.

See code below:

Adding the missing import statement can easily solve the issue, see code below:

Miscellaneous reasons

We have covered some of the main causes of the “cannot find symbol” Java error but occasionally it can also result due to some unexpected reasons. One such case is when attempting to create an object without the new keyword or an accidental semicolon at the wrong place that would terminate the statement at an unexpected point.

Also Read: Functional Interfaces In Java

Some other causes for the cannot find symbol error may include when you forget to recompile the code or you end up using the dependencies with an incompatible version of Java. Building a project with a very old JDK version can also be a reason as well as mistakenly redefining platform or library classes with the same identifier.

Conclusion

We have discussed that the “cannot find symbol Java” error is a Java compile-time error which is encountered whenever an identifier in the source code is not identified by the compiler. Similar to any other compilation error, it is very significant to understand the causes of this error, so that you can easily pinpoint the issue and address it properly.

Once you can discover the reason behind the error, it can be easily resolved as demonstrated by various examples in this article.

Shaharyar Lalani is a developer with a strong interest in business analysis, project management, and UX design. He writes and teaches extensively on themes current in the world of web and app development, especially in Java technology.

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The “Cannot find symbol” compilation error in Java

Table of Contents

When a user refers to a variable that hasn’t been declared in the application, the “can’t find symbol” error occurs. To put it another way, the compiler isn’t aware of the variable’s declaration. For example:

What are possible solutions to this problem?

If you ever encounter this issue, you should review the code for the following scenarios:

• Make sure you’ve declared the variable, for example, int i = 15;. If int has not been written, the error may show.
• Also, see if the defined variable is outside the code, for example, if it is not a member of the HelloCodeunderscored class.
• Make sure you’re using the right case. If you declare a variable as var but access it as Var, it is an example of such a scenario.
• Numbers, dollar signs, and hyphens are not allowed in identifier values; check for them.

Errors in Compilation Time

The compiler examines and checks the code for various things during compilation, including reference types, type casts, and method declarations, to mention a few. This stage of the compilation process is crucial since it is here that we will encounter a compilation mistake.

Compile-time mistakes can be divided into three categories:

Syntax errors

One of the most common programming errors is failing to use a semicolon at the end of a statement; other typical errors include forgetting imports, mismatching parentheses, and omitting the return statement.

Type-checking errors

This is a method of ensuring that our code is type-safe. With this check, we provide that the kinds of expressions are consistent. If we define a variable of type int, we should never assign a value of type double or String to it.

Compiler will crash

Meanwhile, there’s a chance the compiler will crash. It is exceptionally uncommon, but it does happen. In this scenario, it’s good to know that the issue isn’t with our code but with something else.

Compilers follow a set of rules that are specific to each language. If a code doesn’t follow these requirements, the compiler won’t be able to convert it, resulting in a compilation error. The key to resolving the “Cannot find symbol” compilation problem is to figure out what’s causing it.

We may deduce the line of code where the problem occurred and which element is incorrect from the error message. Knowing the most common causes of this mistake will make it easier and faster to resolve.

Symbol Tables: An Overview

Compilers construct and maintain symbol tables, which are significant data structures for storing information related to identifiers in source code. This information is placed into symbol tables during lexical and syntactic analysis and subsequently used in the compilation process.

The identifiers of classes, interfaces, variables, and methods are bound to correspond entries in the symbol tables when the declarations are processed. When these identifiers appear in source code, the compiler looks them up in the symbol tables. It uses that information to confirm that a variable has been declared, establish the variable’s scope, and do type checking to ensure that an expression is semantically correct.

Symbol tables are also employed in the creation and optimization of code. The following is a simplified representation of a symbol table entry (or simply a symbol) in Java:

The comparable notation for a global variable declaration, such as final double ratio, would be .

Error: Cannot Find Symbol

As the name implies, the cannot locate symbol error refers to a symbol that you cannot find. While there are a variety of causes for this, they all boil down to the Java compiler being unable to locate the symbol associated with a given identifier.

Two more fields are included in the compiler’s message for the cannot locate symbol error:

“symbol” refers to the name and type of the referenced identifier. On the other hand, “location” refers to the class where the identifier is used.

What causes the symbol cannot be found error?

The following are the most typical causes of the cannot locate symbol compile-time error:

• Variable and method declarations missing,
• References to variables and methods being out of scope
• misspelled identifiers, and
• omitted import statements.

Symbol Not Found vs. Cannot Find Symbol vs. Cannot Resolve Symbol

The cannot find symbol issue can also be encountered under the words symbol not found and cannot resolve symbol, as different Java compilers use somewhat different wording. Apart from the names, there is no difference between the meanings of these phrases.

Examples of “Cannot Find Symbol Error.”

Some of these “Cannot find symbol error” are as follows:

Handling an undeclared variable

The cannot find symbol error is raised when the Java compiler encounters an identifier it can’t find in the symbol table. As a result, the most common cause of this error is when a reference to an undeclared variable is made. Unlike some other languages, which don’t require explicit variable declarations or may enable declaring a variable after it’s been referenced (through hoisting ), Java requires that a variable be declared before being used or referenced in any form.

Figure (a) shows how an undeclared variable, in this case, the identifier average on line 9, causes two instances of the cannot find symbol error at the code’s locations. Figure (b) resolves the issue by declaring this variable with its data type (or inferring its kind with the var keyword in Java 10+).

Dealing with an Out of scope variable

The compiler throws the cannot find symbol error when a Java application tries to access a variable declared in a separate (non-inherited or non-overlapping) scope. The effort to try and have access to the variable counter on lines 17 and 18 in Figure (a), which is only available within the statement declared on line 11, demonstrates this. Figure (b) indicates that moving the counter variable outside the for loop resolves the problem.

Figures (a) & (b): Error and resolution for not being able to discover a symbol for an out-of-scope variable.

Method name misspelled

A cannot locate symbol error is caused by misspelling an existing method or any valid identifier. Because Java identifiers are case-sensitive, any change of an existing variable, method, class, interface, or package name, as shown in Figure (b), will result in this error.

Error Figure (a) and resolution Figure (b): Cannot find the symbol for a misspelled method name

An import statement is missing

Using classes, whether from the Java platform or a library, necessitates appropriately importing them using the import statement. If you don’t, the Java compiler will complain about a symbol that can’t be found. The java.util package is used in the code sample in Figure (a). The cannot locate symbol issue arises because the list class was created without specifying the necessary import. The problem is solved by adding the missing import statement line 4 in Figure (b).

Figure (a) Error and resolution (b): Cannot find the symbol for missing import

Examples that aren’t as common

The fundamental cause of the Java error cannot locate the symbol is sometimes found in unexpected or hidden areas. It is the case when a sentence is prematurely terminated by an unintentional semicolon Figure (a) or when object creation is attempted without a correct constructor invocation, which must include the new keyword Figure 6.

Unable to locate a symbol for a prematurely stopped loop Figure (a) error and Figure (b) resolution

Figure (a) Error and Figure (b) Resolution for Cannot Find Symbol Constructor Call

Other reasons for the problem “can’t find symbol” include:

Here are a few instances where the “Cannot detect symbol” appears unexplainable until you investigate further.

Inability to find symbol ‘var’:

You’re presumably trying to compile source code with an older compiler or an older—source level that employs local variable type inference (i.e., a var declaration). In Java 10, the var was introduced. Check your JDK version, build files, and IDE settings (if this happens in an IDE).

You’re not compiling or recompiling anything

New Java programmers occasionally don’t grasp how the Java toolchain works or haven’t set up a repeatable “build process,” such as utilizing an IDE, Ant, Maven, Gradle, etc. In this case, the programmer may end up chasing his tail, looking for an imaginary fault that is caused by improper recompilation of the code, and so on.

Another example is when you compile and run a class with (Java 9+) java SomeClass.java. You’re likely to get “Cannot resolve symbol” errors referring to the 2nd class if the class depends on another class that you haven’t compiled (or recompiled). The other source file(s) are not compiled automatically. In addition, the new “compile and execute” mode of the java command isn’t suited for launching programs with multiple source code files.

Incorrect dependencies

If you use an IDE or a build tool that manages the build path and project dependencies, you may have made a mistake with the dependencies; for example, you may have left out a dependency or chosen the incorrect version. Check the project’s build file if you’re using a build tool (Ant, Maven, Gradle, etc.). Further, examine the project’s build path setup if you’re using an IDE.

An issue with a previous build

It’s possible that a previous build failed, so a JAR file was created with missing classes. You would usually note such failure if you were using a build tool. If you acquire JAR files from someone else, you’ll have to rely on them constructing correctly and catching mistakes.

Use tar -tvf when you need to list the suspected JAR files contents if you suspect this.

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Whenever you need to use external classes/interfaces (either user defined or, built-in) in the current program you need to import those classes in your current program using the import keyword.

But, while importing any class −

• If the path of the class/interface you are importing is not available to JVM.

• If the absolute class name you have mentioned at the import statement is not accurate (including packages and class name).

• If you have imported the class/interface used.

You will get an exception saying “Cannot find symbol ……”

Example

In the following example we are trying to read a string value representing the name of the user from key-board (System.in). For this we are using the scanner class of the Java.Util Package.

public class ReadingdData {
   public static void main(String args[]) {
      System.out.println("Enter your name: ");
      Scanner sc = new Scanner(System.in);
      String name = sc.next();
      System.out.println("Hello "+name);
   }
}

Compile time error

Since we are using a class named Scanner in our program and haven’t imported it in our program. On executing, this program generates the following compile time error −

ReadingdData.java:6: error: cannot find symbol
      Scanner sc = new Scanner(System.in);
      ^
   symbol: class Scanner
   location: class ReadingdData
ReadingdData.java:6: error: cannot find symbol
      Scanner sc = new Scanner(System.in);
      ^
   symbol: class Scanner
   location: class ReadingdData
2 errors

Solution

• You need to set class path for the JAR file holding the required class interface.

• Import the required class from the package using the import keyword. While importing you need to specify the absolute name (including the packages and sub packages) of the required class.

Example

 Live Demo

import java.util.Scanner;
public class ReadingdData {
   public static void main(String args[]) {
      System.out.println("Enter your name: ");
      Scanner sc = new Scanner(System.in);
      String name = sc.next();
      System.out.println("Hello "+name);
   }
}

Output

Enter your name:
krishna
Hello krishna