Basic Initialization a Map, List, and Set in Apex

1. List

public list<String> MyList = new list<String> {'AAA', 'AAA', 'BBB', 'BBB', 'CCC'};

2. Set

public set<String> MySet = new set<String> {'A', 'B', 'C', 'D', 'E', 'F', 'G'};

3. Map

public map<String, String> MyMap = new map<String, String> {'KeyValueA' => 'ValueA',

KeyValueB' => 'ValueB', 'KeyValueC' => 'ValueC' };

4. List of Maps

public list<map<String, String>> MyListOfMaps = new list<map<String, String>>

{

new map<String, String>

{'KeyValueA' => 'ValueA',

'KeyValueB' => 'ValueB',

'KeyValueC' => 'ValueC'

},

new map<String, String>

{'KeyValueA' => 'ValueA'

},

};

5. Map of Lists

public map<String, list<String>> MyMap = new map<String, list<String>>

{'KeyValue1' => new list<String> {'ValueA', 'ValueB', 'ValueC'},

'KeyValue2' => new list<String> {'ValueD', 'ValueE', 'ValueF'},

'KeyValue3' => new list<String> {'ValueG', 'ValueH', 'ValueI'}

};

6. Map of Maps

public map<String, map<String, String>> MyMap = new map<String, map<String, String>>

{'KeyValue1' => new map<String, String>

{'KeyValueA' => 'ValueA',

'KeyValueB' => 'ValueB',

'KeyValueC' => 'ValueC'

},

'KeyValue2' => new map<String, String>

{'KeyValueA' => 'ValueA'

},

'KeyValue3' => new map<String, String>

{'KeyValueA' => 'ValueA',

'KeyValueB' => 'ValueB'

}

};