Resolving Package Structure Issues
Another common cause of the 'Cannot Access Class' error is incorrect package structure. In this step, you'll learn how to identify and resolve package structure issues in Java.
Understanding Package Structure in Java
In Java, the package structure must match the directory structure. For example, a class in the com.example.util package must be located in the com/example/util directory.
If the physical directory structure does not match the package declaration, you'll encounter the 'Cannot Access Class' error, even if the access modifiers are correct.
Creating a Class with a Package Structure Issue
Let's create a new Java class with an incorrect package declaration to demonstrate this problem. Create a new file named Logger.java in the src/main/java/com/example/util directory with the following content:
package com.example.logger; // Incorrect package declaration
public class Logger {
public void log(String message) {
System.out.println("LOG: " + message);
}
}
Notice that the package declaration is com.example.logger, but the file is located in the com/example/util directory. This mismatch will cause a 'Cannot Access Class' error.
Now, create a new file named LogTest.java in the src/main/java/com/example/app directory that tries to use the Logger class:
package com.example.app;
import com.example.logger.Logger;
public class LogTest {
public static void main(String[] args) {
Logger logger = new Logger();
logger.log("Testing logger");
}
}
Compiling and Observing the Error
Try to compile your Java project:
./compile.sh
You should see an error message similar to:
src/main/java/com/example/app/LogTest.java:3: error: package com.example.logger does not exist
import com.example.logger.Logger;
^
src/main/java/com/example/app/LogTest.java:6: error: cannot find symbol
Logger logger = new Logger();
^
symbol: class Logger
location: class LogTest
src/main/java/com/example/app/LogTest.java:6: error: cannot find symbol
Logger logger = new Logger();
^
symbol: class Logger
location: class LogTest
3 errors
This error occurs because the compiler cannot find the Logger class in the com.example.logger package, as there is no such package or the directory structure doesn't match the package declaration.
Fixing the Package Structure Issue
There are two ways to fix this issue:
- Change the package declaration to match the directory structure
- Move the file to a directory structure that matches the package declaration
Let's use the first approach. Open the Logger.java file and modify the package declaration to match the directory structure:
package com.example.util; // Correct package declaration
public class Logger {
public void log(String message) {
System.out.println("LOG: " + message);
}
}
Also, update the import statement in the LogTest.java file:
package com.example.app;
import com.example.util.Logger; // Updated import
public class LogTest {
public static void main(String[] args) {
Logger logger = new Logger();
logger.log("Testing logger");
}
}
Recompiling and Testing the Solution
Now, recompile your Java project:
./compile.sh
The compilation should now succeed without errors. Let's create a simple script to run the LogTest class:
echo "java -cp bin com.example.app.LogTest" > ./runlog.sh
chmod +x ./runlog.sh
Now run the LogTest class:
./runlog.sh
You should see the following output:
LOG: Testing logger
This confirms that our LogTest class can now access the Logger class because the package declaration matches the directory structure.
Understanding the Solution
When you encounter a 'Cannot Access Class' error, always check that:
- The package declaration in the source file matches the directory structure
- The import statements correctly reference the package where the class is located
By ensuring these two conditions are met, you can avoid many 'Cannot Access Class' errors in your Java projects.
