Exceptions in Salesforce

DML Exceptions

Any problem with a DML statement, such as an insert statement missing a required field on a record.

ListException

Any problem with a list, such as attempting to access an index that is out of bounds.

1. try
2. {
3.     List<Integer> li = new List<Integer>();
4.     li.add(15);
5.     // This list contains only one element, but we're attempting to access the second element from this zero-based list.
6.     Integer i1 = li[0];
7.     Integer i2 = li[1]; // Causes a ListException
8. }
9. catch(ListException le)
10. {
11.     System.debug('The following exception has occurred: ' + le.getMessage());
12. }

Debug log will be: The following exception has occurred: List index out of bounds: 1 .

NullPointerException

Any problem with dereferencing a null variable.

Try out some code that does some things on purpose to cause this exception to be thrown. Execute the following:

1. try
2. {
3.     String s;
4.     Boolean b = s.contains('abc'); // Causes a NullPointerException
5. }
6. catch(NullPointerException npe)
7. {
8.     System.debug('The following exception has occurred: ' + npe.getMessage());
9. }

Debug will be: The following exception has occurred: Attempt to de-reference a null object

QueryException

Any problem with SOQL queries, such as assigning a query that returns no records or more than one record to a singleton sObject variable.

1. try
2. {
3.     // This statement doesn't cause an exception, even though we don't have a merchandise with name='XYZ'.
4.     // The list will just be empty.
5.     List<Merchandise__c> lm = [SELECT Name FROM Merchandise__c WHERE Name='XYZ'];
6.     // lm.size() is 0
7.     System.debug(lm.size());
8.     // However, this statement causes a QueryException because we're assiging the return value to a Merchandise__c object but no Merchandise is returned.
9.     Merchandise__c m = [SELECT Name FROM Merchandise__c WHERE Name='XYZ' LIMIT 1];
10. }
11. catch(QueryException qe)
12. {
13.     System.debug('The following exception has occurred: ' + qe.getMessage());
14. }

Debug log will be The following exception has occurred: List has no rows for assignment to SObject .

SObjectException

Any problem with sObject records, such as attempting to change a field in an update statement that can only be changed during insert .

Try out some code that does some things on purpose to cause this exception to be thrown. Execute the following:

1. try
2. {
3.     Merchandise__c m = [SELECT Name FROM Merchandise__c LIMIT 1]; // Here No use of Limit.
4.     // Causes an SObjectException because we didn't retrieve the Total_Inventory__c field.
5.     Double inventory = m.Total_Inventory__c;
6. }
7. catch(SObjectException se)
8. {
9.     System.debug('The following exception has occurred: ' + se.getMessage());
10. }

Debug log will be: The following exception has occurred: SObject row was retrieved via SOQL without querying the requested field: Merchandise__c.Total_Inventory__c