1. DMLException:

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 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 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());