Salesforce Apex Study Note

Salesforce Apex Tips like

How to get certain days month end day?
How to change the string to date ?
How to Change the date to String with formatting?

How to get certain days month end day?

Date selectedDate = Date.today().addDays(4);
Date firstDate = selectedDate.toStartOfMonth();
p.Date__c =firstDate.addDays(date.daysInMonth(selectedDate.year() , selectedDate.month())  - 1);

Change the string to date

Date x = Date.valueOf('2015-8-11'); 

system.debug('Now '+ x );

Change the date to String with formatting

date InputDate = date.newInstance(2017, 3, 21); 

Integer d = InputDate.day(); 

Integer mo = InputDate.month(); 

Integer yr = InputDate.year(); 

DateTime DT = DateTime.newInstance(yr, mo, d); 

system.debug('Now '+ DT.format('yyyy-MM-dd') );

How can we implement stack concepts in salesforce apex?

public class MyStack {

    private List < sObject > al;
    public MyStack() {
        al = new List < sObject > ();
    }
    public void push(sObject item) {
        al.add(item);
    }
    public sObject pop() {
        if (!isEmpty())
            return al.remove(size() - 1);
        else
            return null;
    }
    public boolean isEmpty() {
        return (al.size() == 0);
    }
    public sObject peek() {
        if (!isEmpty())
            return al.get(size() - 1);
        else
            null;
    }
    public int size() {
        return al.size();
    }

}

SQL –>List–> Map

map<id, User> userMap = new map<id, User>([select ID,ManagerId,Manager.Email from User where id in : OwnerIdSet]);