Java error cannot find symbol ioexception

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.

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:

1. public class MisspelledMethodNameExample {
2.    static int findLarger(int n1, int n2) {
3.      if (n1 > n2) return n1;
4.      if (n2 > n11) return n2;
5.      if (n2 == n11) return -1;
6.    }
7. 
8.    public static void main(String... args) {
9.       int value = findlarger(20, 4); // findlarger ≠ findLarger
10.      System.out.println(value);
11.   }
12. }

MisspelledMethodNameExample.java:9: error: cannot find symbol   
 int value = Fibonacci(20);
              ^
 symbol:   method findLarger(int, int)
  location: class MisspelledMethodNameExample

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:

1. public class UndeclaredVariableExample
2. {
3.     public static void main(String... args) {
4.        int num1 = 5;
5.        int num2 = 10;
6.        int num3 = 43;
7.        sum = (num1 + num2 + num3) // sum is not declared
8.        System.out.println(sum);
9.      }
10. }

UndeclaredVariableExample.java:7: error: cannot find symbol
    sum = (num1 + num2 + num3);
    ^
  symbol:   variable sum
  location: class UndeclaredVariableExample

UndeclaredVariableExample.java:8: error: cannot find symbol
    System.out.println(sum);
                       ^
  symbol:   variable sum
  location: class UndeclaredVariableExample
2 errors

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

See this corrected code below,

1. public class UndeclaredVariableExample
2. {
3.    public static void main(String args) {
4.      int num1 = 5;
5.      int num2 = 10;
6.      int num3 = 43;
7. 
8.      int sum = (num1 + num2 + num3);
9.      System.out.println(sum);
10.     }
11. }

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:

1. public class OutOfScopeExample 
2. {
3.      public static void main(String args) {
4. 
5.             for (int counter = 0; counter < 100; counter++) 
6.             { … }
7. 
8. System.out.println(“Even numbers from 0 to 100”)
9.       if (counter mod 2 == 0) 
10.       {
11.            System.out.println(counter);
12.       }
13.    }
14. }

OutOfScopeVariableExample.java:9: error: cannot find symbol
    if (counter mod 2 == 0)
        ^
  symbol:   variable counter
  location: class OutOfScopeVariableExample

OutOfScopeVariableExample.java:12: error: cannot find symbol
      System.out.println(counter);
                         ^
 symbol:   variable counter
  location: class OutOfScopeVariableExample
2 errors

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

See this code example,

1. public class OutOfScopeExample 
2. {
3.     public static void main(String... args) {
4. 
5.        for (int counter = 0; counter < 100; counter++) 
6.        { 
7.         System.out.println(“Even numbers from 0 to 100”)
8.         if (counter mod 2 == 0) 
9.        {
10.           System.out.println(counter);
11.        }
12.     }
13.   }
14. }

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:

1. public class MissingImportExample {
2. 
3.     public static void main(String args) 
4.     {
5.         double sqrt19 = Math.sqrt(19);
6. System.out.println("sqrt19 = " + sqrt19);
7.    }
8. }

MissingImportExample.java:6: error: cannot find symbol
  double sqrt19 = Math.sqrt(19);
                  ^
  symbol:   class Math
  location: class MissingImportExample

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

1. import java.util.Math;
2. 
3.    public class MissingImporExample {
4. 
5.     public static void main(String args) 
6.    {
7.       double sqrt19 = Math.sqrt(19);
8.  System.out.println("sqrt19 = " + sqrt19);
9.    }
10. }

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.

Пытаюсь скомпилировать через консоль файл result и выдает следующую ошибку(в idea все идеально работает). Есть 2 класса в разных файлах. result — это типо как main

package VSU.CS.VEGA;
import java.io.IOException;

public class result {
    public static void main(String[] args) throws IOException {
        inputAndOutput output = new inputAndOutput();
        String error = "You entered a non-rectangular matrix, please check the data and re-enter.";
        try {
            output.readMtx();
        }
        catch (ArrayIndexOutOfBoundsException exception){
            System.err.print(error);
        }


    }
}

package VSU.CS.VEGA;

import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.lang.ArrayIndexOutOfBoundsException;



public class inputAndOutput {

    void readMtx() throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("input.txt"));

        ArrayList<String> lines = new ArrayList<>();
        while (br.ready()) {
            lines.add(br.readLine());
        }
        int matrixHeight = lines.size();

        int[][] matrix = new int[matrixHeight][];

        for(int i = 0; i < matrixHeight; ++i) {
            String[] nums = lines.get(i).split("s*,s*");
            matrix[i] = new int[nums.length];
            for(int j = 0; j < nums.length; ++j) {
                matrix[i][j] = Integer.parseInt(nums[j]);
            }
        }
        int[][] matrixForOutput = calc(matrix);
        try(PrintWriter out = new PrintWriter(new FileOutputStream("output.txt"))) {
            for (int i = 0; i < matrixHeight; ++i) {
               out.println(Arrays.toString(matrixForOutput[i]).replaceAll("^\[|]$", ""));
            }
        }
        catch (ArrayIndexOutOfBoundsException ignored){
        }


        //out.println(Arrays.toString(matrixForOutput).replaceAll("^\[|]$", ""));
    }

    int[][] calc(int[][] array) {
        int rows = array.length;
        int cols = array[0].length;
        boolean[] minRows = null, maxRows = null;
        boolean[] minCols = null, maxCols = null;

        Integer min = null;
        Integer max = null;

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                if (null == min || array[i][j] < min) {
                    minRows = new boolean[rows];
                    minRows[i] = true;
                    minCols = new boolean[cols];
                    minCols[j] = true;
                    min = array[i][j];
                } else if (array[i][j] == min) {
                    minRows[i] = true;
                    minCols[j] = true;
                }

                if (null == max || array[i][j] > max) {
                    maxRows = new boolean[rows];
                    maxRows[i] = true;
                    maxCols = new boolean[cols];
                    maxCols[j] = true;
                    max = array[i][j];
                } else if (array[i][j] == max) {
                    maxRows[i] = true;
                    maxCols[j] = true;
                }
            }
        }
//  uncomment to debug
//    System.out.println("min=" + min + "; max=" + max);
//    System.out.println("minRows=" + Arrays.toString(minRows));
//    System.out.println("maxRows=" + Arrays.toString(maxRows));
//    System.out.println("minCols=" + Arrays.toString(minCols));
//    System.out.println("maxCols=" + Arrays.toString(maxCols));
        int rowsToDelete = 0, colsToDelete = 0;
        for (int i = 0; i < rows; i++) {
            if (minRows[i] || maxRows[i]) {
                rowsToDelete++;
            }
        }
        for (int i = 0; i < cols; i++) {
            if (minCols[i] || maxCols[i]) {
                colsToDelete++;
            }
        }

        if (rows == rowsToDelete || cols == colsToDelete) {
            return new int[1][0];
        }

        int[][] result = new int[rows - rowsToDelete][cols - colsToDelete];

        for (int i = 0, r = 0; i < rows; i++) {
            if (minRows[i] || maxRows[i])
                continue; // пропустить строку, содержащую минимум или максимум
            for (int j = 0, c = 0; j < cols; j++) {
                if (minCols[j] || maxCols[j])
                    continue; // пропустить столбец, содержащий минимум или максимум
                result[r][c++] = array[i][j];
            }
            r++;
        }
        //out.println(Arrays.toString(array).replaceAll("^\[|]$", ""));

        return result;
    }



}

сама ошибка:

result.java:6: error: cannot find symbol
        inputAndOutput output = new inputAndOutput();
        ^
  symbol:   class inputAndOutput
  location: class result
result.java:6: error: cannot find symbol
        inputAndOutput output = new inputAndOutput();
                                    ^
  symbol:   class inputAndOutput
  location: class result
2 errors

• IOException is a class from the java.io package, so in order to use it, you should add an import declaration to your code. import java.io.*; (at the very top of the java file, between the package name and your class declaration) FileNotFoundException is an IOException. It’s a specialization of IOException. Once you have caught the IOException, the flow of the program will never get to the point of checking for a more specific IOException. Just swap these two, to test for the more specific case first (FileNotFound) and then handle (catch) any other possible IOExceptions.

  
  Was this post helpful?
  thumb_up
  thumb_down
  

• 

  Hi

  Did you tried the following:

  * copy/paste the class file into your project src directory

  * then copy your .java file and recompile it

  * compile the IO.java File before you try and Run

  More details see the answers from this URL:

  http://www.dreamincode.net/forums/topic/54607-making-my-classes-available-to-myself/ Opens a new window Opens a new window

  
  Was this post helpful?
  thumb_up
  thumb_down
  

• Java is «stupid» with imports.  You need to add imports to the top of the file, before any other code.  It can be after the initial comments describing the file but before the first «class» statement.

  Depending on the version of Java, one of the following:

  // Wildcarded import
  import java.IO.*;

  or

  // If IO is a class vs. a namespace (I think this is the correct option)
  import java.IO;

  or

  // IO is a namespace — old method prior to Java 8 requires each method to be listed.
  import java.IO.output;
  import java.IO.inputDouble;
  …

  Thank you for being upfront about this being a class exercise.  A lot of these aren’t identified as such and result in members here getting riled up.  Another good source I have used for Java is google (actually duckduckgo).  For your error message, enter

  java cannot find symbol — variable IO

  into the search engine’s query bar.  Put the language in the search to reduce the number of other language returns.

  
  Was this post helpful?
  thumb_up
  thumb_down
  

• 

  Thanks.. I tried but same.

  

  
  Was this post helpful?
  thumb_up
  thumb_down
  

• tablesalt wrote:

  Thanks.. I tried but same.

  Java is case sensitive.  Notice that I capitalized IO in my examples.

  
  Was this post helpful?
  thumb_up
  thumb_down
  

• 

  What does this error mean?

  The «Cannot find symbol» errors generally occur when you try to
  reference an undeclared variable in your code. A «Cannot find symbol»
  error means that the compiler cannot do this. Your code appears to be
  referring to something that the compiler doesn’t understand.

  What things can cause this error?

  The general causes for a Cannot find symbol error are things like:

  • Incorrect spelling.
  • Wrong case. Halo is different from halo.
  • Improper use of acceptable identifier values (letters, numbers,
    underscore, dollar sign), my-class is not the same as myclass.
  • No variable declaration or variable is outside of the scope you are
    referencing it in.

  More about…cannot find symbol Error Opens a new window Opens a new window

  Dell

  
  Was this post helpful?
  thumb_up
  thumb_down