What is Collections and What are the different collections in Apex?
The Apex supports arrays to store data. Arrays are of a fixed size which is defined during initialization of the array.
Developer typically require a data structure which is
flexible in size, so that they can add and remove items from this data
structure on request. To avoid that every developer has to implement his custom
data structure the Apex library provide several default implementations for
this via the collection.
Apex collections are dynamic in size, e.g. a collection
can contain a flexible number of objects.
More theoretical said, collection is a data structure which
contains and processes a set of data. The data stored in the collection is
encapsulated and the access to the data is only possible via predefined methods.
For example if your application saves data in an object of
type People, you can store several People objects in a collection.
Arrays and collections are a family of data types that
contain a sequence of values . It includes Lists , Arrays, Sets, and Maps.
Each collection type is different, but there are four methods
you can invoke on all of them:
1. clear: Removes all elements from the collection.
2. clone: Returns a copy of the collection.
3. isEmpty: Returns false if the collection has elements,
true if empty.
4. size: Returns the number of elements in the collection as
an Integer.
Array
array, which stores a fixed-size sequential collection of
elements of the same type. An array is used to store a collection of data, but
it is often more useful to think of an array as a collection of variables of
the same type.
Instead of declaring individual variables, such as number0,
number1, ..., and number99, you declare one array variable such as numbers and
use numbers[0], numbers[1], and ..., numbers[99] to represent individual
variables.
Declaring Array Variables:
To use an array in a program, you must declare a variable to
reference the array, and you must specify the type of array the variable can
reference. Here is the syntax for declaring an array variable:
dataType[] arrayRefVar; // preferred way.
EX:-
Account[]
accs = new Account[]{};
Account a
= new Account();
a.name =
'xxx';
accs.add(a);
System.debug(accs[0].name);
a.clear();
System.debug(accs[0].name);
List
A list is an ordered collection of typed primitives,
sObjects, user-defined objects, Apex objects or collections that are
distinguished by their indices.
To declare a list, use the List keyword followed by the
primitive data, sObject, nested list, map, or set type within <>
characters.
for reference
EX: -
//
Create an empty list of String
List<String>
my_list = new List<String>();
//
Create a list of account records from a SOQL query
List<Account>
accs = [SELECT Id, Name FROM Account LIMIT 1000];
The following are instance methods for List.
add(Object)
: Adds an
element to the end of the list.
add(Integer,
Object) :Inserts an element into the list at the specified index position.
addAll(List) :
Adds all of the elements in the specified list to the list that calls the
method. Both lists must be of the same type.
addAll(Set) :Add all of the elements in
specified set to the list that calls the method. The set and the list must be
of the same type.
clear() :Removes all elements from a list,
consequently setting the list's length to zero.
clone() : Makes
a duplicate copy of a list.
deepClone(Boolean, Boolean, Boolean) : Makes a duplicate copy of
a list of sObject records, including the sObject records themselves.
equals(List)
: Compares
this list with the specified list and returns true if both lists are equal; otherwise, returns false.
get(Integer) : Returns the list element
stored at the specified index.
getSObjectType()
: Returns
the token of the sObject type that makes up a list of sObjects.
hashCode() : Returns
the hashcode corresponding to this list and its contents.
isEmpty() : Returns
true if the list has zero elements.
iterator()
: Returns
an instance of an iterator for this list.
remove(Integer) : Removes
the list element stored at the specified index, returning the element that was
removed.
set(Integer, Object) : Sets the
specified value for the element at the given index.
size() : Returns
the number of elements in the list.
sort() : Sorts the items in the
list in ascending order.
public
class arrayListTest {
//creating List
List<String> nameList = new List<String>();
public void addElementsList(){
//Adding string objects to List
nameList.add('Jwalant');
nameList.add('Hiren');
nameList.add('Piyush');
nameList.add('Yogesh');
nameList.add('Dharmendra');
nameList.add('Piyush');
system.debug(‘List
size is-->’+ nameList.size());
//iterating over list
for(String name : nameList){
System.debug('List Elements is-->'+name);
}
}
}
addAll method Example
public
class arrayListAddAllTest {
public static void addAlltest() {
//creating List
List<String> firstList = new List<String>();
//Adding string objects to first List
firstList.add('Jwalant');
firstList.add('Hiren');
firstList.add('Piyush');
system.debug(‘
First List size is-->’+ firstList.size());
//creating ArrayList
List<String> secondList = new List<String>();
//Adding string objects to second List
secondList.add('Yogesh');
secondList.add('Dharmendra');
secondList.add('Piyush');
//add all objects of first list to second list.
secondList.addAll(firstList);
//iterating over second arraylist
for(String name : secondList){
System.debug('Second List Details is-->'+name);
}
}
public static void removeTest() {
//creating List
List<String> firstList = new List<String>();
//Adding string objects to first List
firstList.add('Jwalant');
firstList.add('Hiren');
firstList.add('Piyush');
firstList.remove(2); //remove 2nd position value.
//iterating over second list
for(String name : firstList){
System.debug(name);
}
}
}
Set
A set is an unordered collection of elements that do not contain any
duplicates. Set elements can be of any data type—primitive types, collections,
sObjects, user-defined types and built-in Apex types.
new Set<String>()
The following are ways to declare and populate a set:
for reference
Set<String>
s1 = new Set<String>{'a', 'b + c'}; // Defines a new set with two elements
Set<String>
s2 = new Set<String>(s1); // Defines a new set that contains the
//
elements of the set created in the previous step
The following are instance methods for Set.
add(Object)
: Adds an
element to the set if it is not already present.
addAll(List<Object>)
: Adds all
of the elements in the specified list to the set if they are not already
present.
addAll(Set<Object>)
: Adds all
of the elements in the specified set to the set that calls the method if they
are not already present.
clear() : Removes all of the elements from the set
clone() : Makes a duplicate copy of
the set.
contains(Object)
: Returns true if the set contains the specified element.
containsAll(List<Object>)
: Returns true if the set contains all of the elements in
the specified list. The list must be of the same type as the set that calls the
method.
containsAll(Set<Object>)
: Returns true if the set contains all of the elements in
the specified set. The specified set must be of the same type as the original
set that calls the method.
equals(Set<Object>)
: Compares
this set with the specified set and returns true if both sets are equal; otherwise, returns false.
hashCode()
: Returns
the hashcode corresponding to this set and its contents.
isEmpty()
: Returns true if the set has zero elements.
remove(Object)
: Removes
the specified element from the set if it is present.
removeAll(List<Object>)
: Removes
the elements in the specified list from the set if they are present.
removeAll(Set<Object>)
: Removes
the elements in the specified set from the original set if they are present.
retainAll(List<Object>)
: Retains
only the elements in this set that are contained in the specified list.
retainAll(Set)
: Retains
only the elements in the original set that are contained in the specified set.
size() : Returns the number of elements in the set
(its cardinality).
public
class SetExample {
public
static void setAdd() {
Set<String> countries = new Set<String>();
boolean result = false;
result = countries.add('USA');
System.debug('USA Added '+result);
result = countries.add('CANADA');
System.debug('CANADA Added '+result);
result = countries.add('U.K.');
System.debug('U.K. Added '+result);
result = countries.add('INDIA');
System.debug('INDIA Added '+result);
result = countries.add('CANADA');
System.debug('CANADA Added '+result);
System.debug('Size of set '+countries.size());
for(String country : countries) {
System.debug('Country: '+country);
}
}
}
Map
A map is a collection of key-value pairs where each unique
key maps to a single value. Keys and values can be any data type—primitive
types, collections, sObjects, user-defined types, and built-in Apex types.
Map<String,
String> country_currencies = new Map<String, String>();
Map<ID,
Set<String>> m = new Map<ID, Set<String>>();
clear() : Removes all of the
key-value mappings from the map.
clone() : Makes a duplicate copy of
the map.
containsKey(Object) : Returns true if the map contains a
mapping for the specified key.
deepClone() : Makes a duplicate copy of
a map, including sObject records if this is a map with sObject record values.
equals(Map) : Compares this map with the
specified map and returns true if both maps are equal; otherwise, returns false.
get(Object) : Returns the value to which
the specified key is mapped, or null if the map contains no value for this key.
getSObjectType() : Returns the token of the
sObject type that makes up the map values.
hashCode() : Returns the hashcode
corresponding to this map.
isEmpty() : Returns true if the map
has zero key-value pairs.
keySet() : Returns a set that
contains all of the keys in the map.
put(Object, Object) : Associates the specified value with the
specified key in the map.
putAll(Map) : Copies all of the mappings
from the specified map to the original map.
putAll(sObject[]) : Adds the list of sObject
records to a map declared as Map<ID, sObject> or Map<String,
sObject>.
remove(Key) : Removes the mapping for
the specified key from the map, if present, and returns the corresponding value.
size() : Returns the number of
key-value pairs in the map.
values() : Returns a list that
contains all of the values in the map in arbitrary order.
public
static void mapPut(){
Map<String,String> currencyMap = new Map<String,String>();
currencyMap.put('USA', 'USD');
currencyMap.put('CANADA', 'CAD');
currencyMap.put('Uniter Kingdom', 'GBP');
for(String key : currencyMap.keySet()) {
System.debug('Country: '+key+' Currency: '+currencyMap.get(key));
}
}
public
static void getMapElements() {
Map<String,String> currencyMap = new Map<String,String>();
currencyMap.put('USA', 'USD');
currencyMap.put('CANADA', 'CAD');
currencyMap.put('Uniter Kingdom', 'GBP');
for(String key : currencyMap.keySet()) {
System.debug('Country: '+key+' Currency: '+currencyMap.get(key));
}
}
public static void containsKeyTest() {
Map<String,String> currencyMap = new Map<String,String>();
currencyMap.put('USA', 'USD');
currencyMap.put('CANADA', 'CAD');
currencyMap.put('Uniter Kingdom', 'GBP');
System.debug('Contains USA? :
'+currencyMap.containsKey('USA'));
System.debug('Contains America?: '+currencyMap.containsKey('America'));
}
public
static void keysetTest() {
Map<String,String> currencyMap = new Map<String,String>();
currencyMap.put('USA', 'USD');
currencyMap.put('CANADA', 'CAD');
currencyMap.put('Uniter Kingdom', 'GBP');
for(String key : currencyMap.keySet()) {
System.debug('Country : '+key+' has currency : '+currencyMap.get(key));
}
}
}
Posted in: apex,Array in Apex,Collection methods in apex,collections in Apex,List in Apex,List Methods,Map in apex,Map Methods in apex,Salesforce,Set in Aoex,Set Methods
1 comments:
very informative blog and useful article thank you for sharing with us , keep posting learn more aboutsalesforce training salesforce Online Training
Post a Comment