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How to initialize a map with values

Maps are empty when declared. To initialize a map with values use the following syntax.

In the above example:

In the above example, we have defined a map to hold the products and their respective quantities.
The map key is a string(product) and value is an integer(Quantity).
On the left of the '=>' symbol is the key and on the right is the value.

Map key-value pairs can be directly initialized from a SOQL query. To initialize a map from SOQL, use the following syntax:

In the above example:

In the above example, we have defined a map to hold the account id and account record.
The Map key is an Id and value is an account.
Apex can automatically map the Id to the key and the corresponding record to the value from an SOQL query list.