公式サイトの情報

https://developer.salesforce.com/docs/atlas.ja-jp.apexcode.meta/apexcode/apex_map_sobject.htm

参考コード

// Populate map from SOQL query
Map<ID, Account> m = new Map<ID, Account>([SELECT Id, Name FROM Account LIMIT 10]);
// After populating the map, iterate through the map entries
for (ID idKey : m.keyset()) {
    Account a = m.get(idKey);
    System.debug(a);
}

以上