Understanding Expressions

An expression is a construct made up of variables, operators, and method invocations that evaluates to a single value. In Apex, an expression is always one of the following types:

• A literal expression. For example:
  11 + 1

• A new sObject, Apex object, list, set, or map. For example:
  1new Account(<field_initializers>)
  2new Integer[<n>]
  3new Account[]{<elements>}
  4new List<Account>()
  5new Set<String>{}
  6new Map<String, Integer>()
  7new myRenamingClass(string oldName, string newName)

• Any value that can act as the left-hand of an assignment operator (L-values), including variables, one-dimensional list positions, and most sObject or Apex object field references. For example:
  1Integer i
  2myList[3]
  3myContact.name
  4myRenamingClass.oldName

• Any sObject field reference that is not an L-value, including:
  • The ID of an sObject in a list (see Lists)
  • A set of child records associated with an sObject (for example, the set of contacts associated with a particular account). This type of expression yields a query result, much like SOQL and SOSL queries.
• A SOQL or SOSL query surrounded by square brackets, allowing for on-the-fly evaluation in Apex. For example:
  1Account[] aa = [SELECT Id, Name FROM Account WHERE Name ='Acme'];
  2Integer i = [SELECT COUNT() FROM Contact WHERE LastName ='Weissman'];
  3List<List<SObject>> searchList = [FIND 'map*' IN ALL FIELDS RETURNING Account (Id, Name), Contact, Opportunity, Lead];

  For information, see SOQL and SOSL Queries.

• A static or instance method invocation. For example:
  1System.assert(true)
  2myRenamingClass.replaceNames()
  3changePoint(new Point(x, y));