List Class

Signature

public List<T>()

Example

// Create a list
List<Integer> ls1 = new List<Integer>();
// Add two integers to the list
ls1.add(1);
ls1.add(2);

Signature

public List<T>(List<T> listToCopy)

Parameters

listToCopy

Type: List<T>

The list containing the elements to initialize this list from. T is the data type of the list elements.

Example

List<Integer> ls1 = new List<Integer>();
ls1.add(1);
ls1.add(2);
// Create a list based on an existing one
List<Integer> ls2 = new List<Integer>(ls1);
// ls2 elements are copied from ls1
System.debug(ls2);// DEBUG|(1, 2)

Signature

public List<T>(Set<T> setToCopy)

Parameters

setToCopy

Type: Set<T>

The set containing the elements to initialize this list with. T is the data type of the set elements.

Example

Set<Integer> s1 = new Set<Integer>();
s1.add(1);
s1.add(2);
// Create a list based on a set
List<Integer> ls = new List<Integer>(s1);
// ls elements are copied from s1
Assert.isTrue(ls.contains(2));
Assert.isTrue(ls.contains(1));

Signature

public Void add(Object listElement)

Parameters

listElement

Type: Object

Return Value

Type: Void

Example

List<Integer> myList = new List<Integer>();
myList.add(47);
Integer myNumber = myList.get(0);
system.assertEquals(47, myNumber);

Signature

public Void add(Integer index, Object listElement)

Parameters

index

Type: Integer

listElement

Type: Object

Return Value

Type: Void

Example

In this example, a list with six elements is created. Integers are added to the first and second index positions, and the subsequent elements are shifted to the right. After the two methods are called, the list has eight total elements.

List<Integer> myList = new Integer[6];
myList.add(0, 47);
myList.add(1, 52);
system.debug(myList); // DEBUG|(47, 52, null, null, null, null, null, null)
system.assertEquals(52, myList.get(1));

Signature

public Void addAll(List fromList)

Parameters

fromList

Type: List

Return Value

Type: Void

Signature

public Void addAll(Set fromSet)

Parameters

fromSet

Type: Set

Return Value

Type: Void

Signature

public Void clear()

Return Value

Type: Void

Signature

public List<Object> clone()

Return Value

Type: List<Object>

Usage

The cloned list is of the same type as the current list.

Note that if this is a list of sObject records, the duplicate list will only be a shallow copy of the list. That is, the duplicate will have references to each object, but the sObject records themselves will not be duplicated. For example:

To also copy the sObject records, you must use the deepClone method.

Example

Account a = new Account(Name='Acme', BillingCity='New York');

Account b = new Account();
Account[] q1 = new Account[]{a,b};

Account[] q2 = q1.clone();
q1[0].BillingCity = 'San Francisco';

System.assertEquals(
      'San Francisco',
      q1[0].BillingCity);
System.assertEquals(
      'San Francisco', 
      q2[0].BillingCity);

Signature

public Boolean contains(Object listElement)

Parameters

listElement

Type: Object

Return Value

Type: Boolean

Example

List<String> myStrings = new List<String>{'a', 'b'};
Boolean result = myStrings.contains('z');
System.assertEquals(false, result);

Signature

public List<Object> deepClone(Boolean preserveId, Boolean preserveReadonlyTimestamps, Boolean preserveAutonumber)

Parameters

preserveId

Type: Boolean

The optional preserveId argument determines whether the IDs of the original objects are preserved or cleared in the duplicates. If set to true, the IDs are copied to the cloned objects. The default is false, that is, the IDs are cleared.

preserveReadonlyTimestamps

Type: Boolean

The optional preserveReadonlyTimestamps argument determines whether the read-only timestamp and user ID fields are preserved or cleared in the duplicates. If set to true, the read-only fields CreatedById, CreatedDate, LastModifiedById, and LastModifiedDate are copied to the cloned objects. The default is false, that is, the values are cleared.

preserveAutonumber

Type: Boolean

The optional preserveAutonumber argument determines whether the autonumber fields of the original objects are preserved or cleared in the duplicates. If set to true, auto number fields are copied to the cloned objects. The default is false, that is, auto number fields are cleared.

Return Value

Type: List<Object>

Usage

The returned list is of the same type as the current list.

To make a shallow copy of a list without duplicating the sObject records it contains, use the clone method.

Example

This example performs a deep clone for a list with two accounts.

Account a = new Account(Name='Acme', BillingCity='New York');

Account b = new Account(Name='Salesforce');

Account[] q1 = new Account[]{a,b};

Account[] q2 = q1.deepClone();
q1[0].BillingCity = 'San Francisco';

System.assertEquals(
     'San Francisco', 
     q1[0].BillingCity);

System.assertEquals(
     'New York',
     q2[0].BillingCity);

insert q1;

List<Account> accts = [SELECT CreatedById, CreatedDate, LastModifiedById, 
                       LastModifiedDate, BillingCity 
                       FROM Account 
                       WHERE Name='Acme' OR Name='Salesforce'];

// Clone list while preserving timestamp and user ID fields.
Account[] q3 = accts.deepClone(false,true,false);

// Verify timestamp fields are preserved for the first list element. 
System.assertEquals(
    accts[0].CreatedById, 
    q3[0].CreatedById);
System.assertEquals(
    accts[0].CreatedDate, 
    q3[0].CreatedDate);
System.assertEquals(
    accts[0].LastModifiedById,
    q3[0].LastModifiedById);
System.assertEquals(
    accts[0].LastModifiedDate,
    q3[0].LastModifiedDate);

Signature

public Boolean equals(List list2)

Parameters

list2

Type: List

The list to compare this list with.

Return Value

Type: Boolean

Usage

Two lists are equal if their elements are equal and are in the same order. The == operator is used to compare the elements of the lists.

The == operator is equivalent to calling the equals method, so you can call list1.equals(list2); instead of list1 == list2;.

Signature

public Object get(Integer index)

Parameters

index

Type: Integer

Return Value

Type: Object

Usage

To reference an element of a one-dimensional list of primitives or sObjects, you can also follow the name of the list with the element's index position in square brackets as shown in the example.

Example

List<Integer> myList = new List<Integer>();
myList.add(47);
Integer myNumber = myList.get(0);
system.assertEquals(47, myNumber);

List<String> colors = new String[3];
colors[0] = 'Red';
colors[1] = 'Blue';
colors[2] = 'Green';

Signature

public Schema.SObjectType getSObjectType()

Return Value

Type: Schema.SObjectType

Usage

Use this method with describe information to determine if a list contains sObjects of a particular type.

Note that this method can only be used with lists that are composed of sObjects.

For more information, see Understanding Apex Describe Information.

Example

// Create a generic sObject variable.
SObject sObj = Database.query('SELECT Id FROM Account LIMIT 1');

// Verify if that sObject  variable is an Account token.
System.assertEquals(
   Account.sObjectType, 
   sObj.getSObjectType());

// Create a list of generic sObjects.
List<sObject> q = new Account[]{};

// Verify if the list of sObjects 
// contains Account tokens.
System.assertEquals(
   Account.sObjectType, 
   q.getSObjectType());

Signature

public Integer hashCode()

Return Value

Type: Integer

Signature

public Integer indexOf(Object listElement)

Parameters

listElement

Type: Object

Return Value

Type: Integer

Example

List<String> myStrings = new List<String>{'a', 'b', 'a'};
Integer result = myStrings.indexOf('a');
System.assertEquals(0, result);

Signature

public Boolean isEmpty()

Return Value

Type: Boolean

Signature

public Iterator iterator()

Return Value

Type: Iterator

Usage

From the returned iterator, you can use the iterable methods hasNext and next to iterate through the list.

See Custom Iterators.

Example

public class CustomIterator
   implements Iterator<Account>{ 
 
   private List<Account> accounts;
   private Integer currentIndex;
 
   public CustomIterator(List<Account> accounts){
       this.accounts = accounts;
       this.currentIndex = 0;
   }
 
   public Boolean hasNext(){ 
       return currentIndex < accounts.size();
   }    
 
   public Account next(){
       if(hasNext()) {
           return accounts[currentIndex++];
       } else {
           throw new NoSuchElementException('Iterator has no more elements.');
       }
   } 
}

Signature

public Object remove(Integer index)

Parameters

index

Type: Integer

Return Value

Type: Object

Example

List<String> colors = new String[3];
colors[0] = 'Red';
colors[1] = 'Blue';
colors[2] = 'Green';
String s1 = colors.remove(2);
system.assertEquals('Green', s1);

Signature

public Void set(Integer index, Object listElement)

Parameters

index

Type: Integer

The index of the list element to set.

listElement

Type: Object

The value of the list element to set.

Return Value

Type: Void

Usage

To set an element of a one-dimensional list of primitives or sObjects, you can also follow the name of the list with the element's index position in square brackets.

Example

List<Integer> myList = new Integer[6];
myList.set(0, 47);
myList.set(1, 52);
system.assertEquals(52, myList.get(1));

List<String> colors = new String[3];
colors[0] = 'Red';
colors[1] = 'Blue';
colors[2] = 'Green';

Signature

public Integer size()

Return Value

Type: Integer

Example

List<Integer> myList = new List<Integer>();
Integer size = myList.size();
system.assertEquals(0, size);

List<Integer> myList2 = new Integer[6];
Integer size2 = myList2.size();
system.assertEquals(6, size2);

Signature

public Void sort()

Return Value

Type: Void

Usage

Using this method, you can sort primitive types, SelectOption elements, and sObjects (standard objects and custom objects). For more information on the sort order used for sObjects, see Sorting Lists of sObjects. You can sort custom types (your Apex classes) if they implement the Comparable interface. Alternatively, a class implementing the Comparator interface can be passed as a parameter to the List.sort method.

When you use sort() methods on List<Id>s that contain both 15-character and 18-character IDs, IDs for the same record sort together in API version 35.0 and later.

Example

In the following example, the list has three elements. When the list is sorted, the first element is null because it has no value assigned. The second element and third element have values of 5 and 10.

List<Integer> q1 = new Integer[3];

 

// Assign values to the first two elements.

q1[0] = 10;

q1[1] = 5;

 

q1.sort();

// Verify sorted list. Elements are sorted in nulls-first order: null, 5, and 10

system.assertEquals(null, q1.get(0));

system.assertEquals(5, q1.get(1));

system.assertEquals(10, q1.get(2));

Signature

public String toString()

Return Value

Type: String

Usage