APEX CODING TIPS

Assigning Query to string variable for using as a parameter.... [SELECT ID FROM Merchandise__c WHERE NAME = 'Coffeemaker'] to a string for passing in to a method String s= 'select id from Merchandise__c where name = \' coffee maker \''; \’ – will be counted for ‘ when the string is evaluated.

Public List<sObject> sObjectVariable{get;set;} sObjectVariable = new List<sObject>();

implements keyword is used to indicate interface implementation

static keyword indicates a class variable (or method) accessible without an instance of the class

final keyword indicates a constant. 

To deliberately cause the DMLException to improve your code coverage and check the functionality of the exception handling.

try {

    // If you can't manipulate the Apex methods input or database state to cause a
    // DMLExcpetion then you can deliberately cause the DMLException to improve your
    // code coverage and check the functionality of the exception handling.
    // You could also use a flag set from your test method to indicate that the 
    // exception should be thrown
    if(Test.isRunningTest()) {
        // Cause DMLException
        insert new Lead();
    }

} catch (DMLException ex) {
    // Existing exception handling.        
}