Apex Maps and Sets Example

apex-maps-example

Account a = new Account(Name = 'Foo');

// not recommended!
Map<Account, String> stringsByAccounts = new Map<Account, String>();
Set<Account> accountSet = new Set<Account>{};
stringsByAccounts.put(a, 'Bar');
accountSet.add(a);

// things are OK as long as you don't mutate 'a'
System.assertEquals('Bar', stringsByAccounts.get(a));
System.assertEquals(true, accountSet.contains(a));

// key mutation
a.Name = 'Bar';

// Map value inaccessible
System.assertEquals(null, stringsByAccounts.get(a));

// Set contains doesn't work
System.assertEquals(false, accountSet.contains(a));

// ... even though the it's still in the set
System.assertEquals(1, accountSet.size());

// if we flip back, everything works again!
a.Name = 'Foo';
System.assertEquals('Bar', stringsByAccounts.get(a));
System.assertEquals(true, accountSet.contains(a));

// 'a2' has the same field values as 'a'
Account a2 = new Account(Name = 'Foo');

System.assertEquals(a,a2);
System.assertEquals(System.hashCode(a),System.hashCode(a2));

// Maps and Sets can't distinguish 'a' vs 'a2'
System.assertEquals('Bar', stringsByAccounts.get(a2));
System.assert(accountSet.contains(a2));

// putting a value for 'a2' into the map overwrites 'a' value 'Bar'
stringsByAccounts.put(a2,'BarBar');
System.assertEquals('BarBar', stringsByAccounts.get(a));