Common Java Errors and How to Fix Them
Browse all documented Java errors with detailed explanations, root causes, and step-by-step fixes.
Cannot find symbol: method add(int, Person) in class com.example.Person
This error occurs when the Java compiler cannot find a method or field that is supposed to exist in a class. This is oft…
Invalid data type for column 'email' in SQL statement.
This error occurs when there is a mismatch between the data type of the column in the database and the data type of the …
java.lang.StackOverflowError at Main.main(Main.java:12) - This thread has been a
A StackOverflowError occurs when a method calls itself recursively without a proper base case, leading to an infinite re…
Cannot find symbol: variable 'employee' in method 'int main(java.lang.String[])'
This error occurs when Java cannot find a declared variable or method within the current scope. This can be caused by a …
Parameter 'username' not found in the query: SELECT * FROM users WHERE username
This error occurs when the JDBC driver or Hibernate is unable to find a parameter in a SQL query. This can happen if the…
Syntax error on token "int", @ expected after this token
This error occurs when the Java compiler encounters a syntax error in the code. In this case, the token "int" is not all…
Syntax error on token "class", delete this token
This error occurs when the Java compiler encounters an invalid or unexpected token in the code, often due to incorrect f…
Cannot find symbol: method System.out.println() is undefined for the type String
This error occurs when Java compiler is unable to find a method or variable that is being referenced in your code.…
Parameter index out of range: 3, number of parameters: 2
This error occurs when a prepared statement is executed with a parameter index that does not exist in the SQL query. It …
Cannot find symbol: variable 'x' in /home/user/java/project/src/MyClass.java on
The 'Cannot find symbol' error occurs when the Java compiler cannot find a declared variable, method, or class. This usu…
Cannot find symbol: method 'equals(Object)' in class 'MyString'
This error occurs when the Java compiler is unable to find a method declaration in the class or interface being used. In…
java.util.ConcurrentModificationException: null at java.base/java.util.ArrayList
This error occurs when a program attempts to modify a collection (like an ArrayList or HashSet) while it is being iterat…
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