Salesforce Apex: Tips and Tricks

Generate a set of Ids from a List of SObject

List<Account> accounts = [SELECT Id, Name FROM Account];
Set<Id> selectedIds = new Map<Id, SObject>(accounts).keySet();
System.debug(selectedIds);

Division of 2 numbers

public static Decimal divide(Integer numerator, Integer denominator) {
    Decimal result;
    if (denominator != 0) {
        result = Decimal.valueOf(Double.valueOf(numerator) / Double.valueOf(denominator));
        return result.setScale(2);
    }
    return 0;
}

Formatting time in Apex
https://paulforce.wordpress.com/2009/08/27/formatting-time-in-apex/