Common Java Errors and How to Fix Them
Browse all documented Java errors with detailed explanations, root causes, and step-by-step fixes.
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…
The final field 'name' in a class cannot be modified once the instance is create
This error occurs when a developer tries to declare a variable as 'final' but still attempts to change its value after i…
SQLSyntaxErrorException: ORA-00933: SQL command not properly ended
This error occurs when the SQL query is not properly formatted or ended, resulting in a syntax error. This can happen wh…
Cannot invoke "java.util.concurrent.ConcurrentHashMap.put(K, V)" because the fol
This error occurs when a method or constructor may throw an exception, but you're trying to call it in a context where e…
org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying b
This error occurs when Spring (a popular Java framework) is unable to find a bean (a managed object) of a specific type,…
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
This error occurs when the Java Virtual Machine (JVM) runs out of memory, typically due to a large heap size or insuffic…
Syntax error on token 'int', delete this token
This error occurs when the compiler encounters unexpected syntax in the code, making it difficult to parse and compile.…
Cannot find symbol. Symbol: method 'toString()' variable 'student' is defined in
This error occurs when the Java compiler is unable to find a method, class, or variable that is being referenced in the …
Cannot find symbol: method get(int) in class java.util.ArrayList
This error occurs when the Java compiler cannot find a method declaration in the class or interface that you are trying …
Syntax error on token "return", { expected after this token
This error occurs when Java encounters syntax that does not conform to the language's rules. In this case, Java is expec…
Parameter index out of range: 2, query was: SELECT * FROM users WHERE username =
This error occurs when the number of parameters in a SQL query does not match the number of placeholders (represented by…
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 …
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