collection

COLLECTIONS: like an array
To Store a group of values
1.List
2.Set
3.Map

LIST:
List<data type> variable-name;
When we have to assign the value to a variable, instantiate(allocating some memory) it

[php]List<data type> variable-name=new List<data type>();<br />Ex:List<String> strlist=new List<String>();[/php]

// List is an ordered collection of similar data types
// List allows duplicate elements

[php]List&lt;String&gt;strList=new list&lt;String&gt;()<br />strList.add('Red');<br />strList.add('Blue');<br />strList.add('Green');<br />strList.add('Red');<br />strList.add('Red');<br />strList.add('Red');<br />
<br />System.debug('StrList'+ strList);[/php]

// Set is an unordered collection of Similar data Types
// Set does not allow duplicat elements

[php]Set<String> strSet=new Set<String>();<br /> StrSet.add('Red');<br /> StrSet.add('Red');<br /> StrSet.add('Red');<br /> StrSet.add('Red');<br /> StrSet.add('Red');<br /> StrSet.add('Blue');<br /> System.debug('StrSet'+ strSet);[/php]

————————————-

[php]List<Account> accList=new List<Account>([Select id,name from Account]);<br /> System.debug(accList);[/php]

(OR)

[php]List<Account> accList=new List<Account>();<br /> acclist=[Select id,Name from Account];<br /> system.debug('Account List'+accList);[/php]

Result:

Sorting order from SOQL

[php]List<Account> accList=new List<Account>([Select id,name from Account order by Name desc]);<br /> System.debug(accList);[/php]

Find the accList size

[php]system.debug('No of elements in the list are '+accList.size());[/php]