Salesforce Apex Map Class Guide

The Salesforce Apex Map class is a collection type that stores data as key-value pairs. It allows you to store and retrieve data based on a unique key that you define. The Map class is similar to a dictionary or a hash table in other programming languages.

Introduction

You will find detailed informations of the common map methods in this article.

But let’s get you started quickly.

We create a map.

Map<String, Integer> nameAndAge = new Map<String, Integer>();

The map is empty.

System.assert(nameAndAge.isEmpty());

We need to put something into the map.

nameAndAge.put('Sally', 33);

Now the map is not empty anymore. It has one key-value pair.

System.assertEquals(1,nameAndAge.size());

But how do we get the age of Sally out of the map?

System.assertEquals(33,nameAndAge.get('Sally'));

Finally, we clean up and remove Sally from the map.

nameAndAge.remove('Sally');

You’ve seen the basic interaction with a map!

Apex map methods

Let’s take a look at the most common Salesforce Apex Map methods.

clear

In case you want an empty map as if it was new, call the map clear method which removes all key-value pairs of the map.

<Map>.clear

Void clear())

Deletes all the key-value pairs from the map.

Return value

Void: The clear method returns nothing.

Example

Map<String, Integer> nameAndAge = new Map<String, Integer>();
nameAndAge.put('Sally',37);
nameAndAge.put('John',21);
System.assertEquals(2,nameAndAge.size());

nameAndAge.clear();
System.assertEquals(0,nameAndAge.size());

containsKey

To check whether a key is already in a map or not, use the containsKey method.

<Map>.containsKey

Boolean containsKey(Object key))

If the map has a mapping for the specified key, it will return true.

Input parameter

key (Object): The key to search for in the map.

Return value

Boolean: True, if this map contains the given key. False, if the key is not in the map.

Example

Map<String, Integer> nameAndAge = new Map<String, Integer>();
nameAndAge.put('Sally',37);

System.assertEquals(true,nameAndAge.containsKey('Sally'));
System.assertEquals(false,nameAndAge.containsKey('Mike'));

get

To retrieve a value from your map, use the get method and pass the required key as parameter.

<Map>.get

Object get(Object key))

Returns the value associated with the specified key in the map, or null if there is no value mapped to the key in the map.

Input parameter

key (Object): The key for the requested value.

Return value

Object: The value for the given key. Null, if there is no value.

Example

Map<String, Integer> nameAndAge = new Map<String, Integer>();
nameAndAge.put('Sally',37);

System.assertEquals(37,nameAndAge.get('Sally'));
System.assertEquals(null,nameAndAge.get('Mike'));

isEmpty

To check if a map is empty in Apex, use the isEmpty method.

<Map>.isEmpty

Boolean isEmpty())

Returns true if the map contains no key-value pairs.

Return value

Boolean: True, if there are no key-value pairs in the map, false if there are pairs int the map.

Example

Map<String, Integer> nameAndAge = new Map<String, Integer>();
System.assertEquals(true, nameAndAge.isEmpty());

nameAndAge.put('Sally',37);
System.assertEquals(false, nameAndAge.isEmpty());

keySet

Need to know, which keys are used within your map? Use the keySet method to retrieve all keys of a map.

<Map>.keySet

Set<Object> keySet())

It returns a set that includes all the keys present in the map.

Return value

Set<Object>: A set that includes all the keys present in the map.

Example

Map<String, Integer> nameAndAge = new Map<String, Integer>();
nameAndAge.put('Sally',37);
nameAndAge.put('Mike',21);

Set<String> keys= nameAndAge.keySet();

System.assert(keys.contains('Sally'));
System.assert(keys.contains('Mike'));

put

The map put method lets you add key-value pairs to a map.

<Map>.put

Object put(Object key, Object value))

Adds a key-value pair to the map or updates the value if the key already exists.

Input parameter

key (Object): The key which is used to find the value.
value (Object): The value that can be found under the given key.

Return value

Object: If the map previously contained a mapping for this key, the old value is returned. If there is no old value, null is returned.

Example

Map<String, Integer> myMap = new Map<String, Integer>();
Object oldValue = myMap.put('Sally', 33);
System.assertEquals(null,oldValue);
oldValue = myMap.put('Sally', 27);
System.assertEquals(33,oldValue);
System.assertEquals(27,myMap.get('Sally'));

remove

The map remove method lets you remove a key-value pair of your map.

<Map>.remove

Object remove(Object key))

If the specified key exists in the map, this operation removes the mapping associated with that key and returns the corresponding value.

Input parameter

key (Object): The string that should be replaced.

Return value

Object: The value of the removed object key-value pair. Null, if there is no value for the given key.

Example

Map<String, Integer> myMap = new Map<String, Integer>();
Object value = myMap.remove('Sally');
System.assertEquals(null,value);
myMap.put('Sally', 33);
value = myMap.remove('Sally');
System.assertEquals(33,value);

size

The size method lets you check how many key-value pairs are in you map-

<Map>.size

Integer size())

Returns the count of key-value pairs present in the map.

Return value

Integer: The count of key-value pairs present in the map.

Example

Map<String, Integer> myMap = new Map<String, Integer>();
System.assertEquals(0,myMap.size());
myMap.put('Sally', 33);
System.assertEquals(1,myMap.size());

values

To get all values from a map, use the Apex map values method.

<Map>.values

List<Object> values())

Returns a list that includes all the values stored in the map.

Return value

List<Object>: A list that includes all the values stored in the map.

Example

Map<String, Integer> myMap = new Map<String, Integer>(); 
myMap.put('Sally', 33); 
myMap.put('Mike', 35);
List<Integer> values  = myMap.values();
System.assertEquals(true,values.contains(33));
System.assertEquals(true,values.contains(35));