1. DML Exception:
DML Exceptions are exceptions that occur whenever a DML operation fails. This may happen due to many reasons, the most common one is inserting a record without a required field.
Ex: try
{
Position__c pos = new Position__c();
insert pos;
}
catch(DmlException e)
{
System.debug(‘The following exception has occurred: ‘ + e.getMessage());
}
2. ListException:
ListException catches any type of run time error with a list. This list can be of any data type such as integer, string, or sObject.
Ex: try
{
List<String> stringList = new List<String>();
stringList.add(‘Bhavna’);
// This list contains only one element,
// but we will attempt to access the second element
// from this zero-based list.
String str1 = stringList[0]; //this will execute fine
String str2 = stringList[1]; // Causes a ListException
}
catch(ListException le)
{
System.debug(‘The following exception has occurred: ‘ + le.getMessage());
}
3. NullPointerException:
NullPointer Exception catches exceptions that occur when we try to reference a null variable. Use this exception whenever you are referencing a variable that might turn out to be null.
Ex: try
{
String stringVariable;
Boolean boolVariable = stringVariable.contains(‘John’);
// Causes a NullPointerException
}
catch(NullPointerException npe)
{
System.debug(‘The following exception has occurred: ‘ + npe.getMessage());
}
4. QueryException:
QueryException catches any run time errors with SOQL queries. QueryException occurs when there is a problem in SOQL queries such as assigning a query that returns no records or more than one record to a single sObject variable.
Ex: try {
// This statement doesn’t cause an exception,
// if we don’t have a problem in SOQL Queries.
// The list will just be empty.
List<Position__c> positionList = [SELECT Name FROM Position__c WHERE Name=’Salesforce Developer’];
// positionList.size() is 0
System.debug(positionList.size());
// However, this statement causes a QueryException because
// we’re assiging the query result to a Position sObject varaible
// but no Position record is found
Position__c pos = [SELECT Name FROM Position__c WHERE Name=’Salesforce Developer’ LIMIT 1];
}
catch(QueryException ge) {
System.debug(‘The following exception has occurred: ‘ + ge.getMessage());
}
5. Generic Exception:
This exception type can catch any type of exception; that’s why it’s called a generic Exception type. This is used when you are not sure which exception type to use and what exception might occur in the code.
Ex: try {
List<Position__c> positionList = [SELECT Name FROM Position__c WHERE Name=’Salesforce Developer’];
// positionList.size() is 0
System.debug(positionList.size());
Position__c pos = [SELECT Name FROM Position__c WHERE Name=’Salesforce Developer’ LIMIT 1];
} catch(Exception ex) {
System.debug(‘The following exception has occurred: ‘ + ex.getMessage());
}
Common Exception Methods:
All Exception types are Exception classes and these classes have methods that can provide a lot of information about the exception and error that occurred.
- getTypeName(): Returns the type of exception, such as DmlException, ListException, and QueryException.
- getMessage(): Returns the error message and displays it for the user.
- getCause(): Returns the cause of the exception as an exception object.
- getLineNumber(): Returns the line number from where the exception was thrown.
- getStackTraceString(): Returns the stack trace as a string.
Ex: try {
Position__c pos = new Position();
// Causes an QueryException because
// we are inserting record without required fields
insert pos;
}
catch(Exception e)
{
System.debug(‘Exception type caught: ‘ + e.getTypeName());
System.debug(‘Message: ‘ + e.getMessage());
System.debug(‘Cause: ‘ + e.getCause()); // returns null
System.debug(‘Line number: ‘ + e.getLineNumber());
}
USER_DEBUG|[6]|DEBUG|Exception type caught: System.QueryException
USER_DEBUG|[7]|DEBUG|Message: List has no rows for assignment to SObject
USER_DEBUG|[8]|DEBUG|Cause: null
USER_DEBUG|[9]|DEBUG|Line number: 2
USER_DEBUG|[10]|DEBUG|Stack trace: AnonymousBlock: line 2, column 1
