Create  an object Trailhead with below fields

Alphabet is controlling picklist with values

A,B,C,D,E

Alphabet Version is dependent picklist with values corresponding to each controlling value

A - A1,A2,A3,A4

B - B1,B2,B3,B4

C - C1,C2,C3,C4

D - D1,D2,D3,D4

E - E1,E2,E3,E4

Selected Alphabet - Long text area

Selected Alphabet Version - Long text area

Create Visualforce page to show below info

Show both picklists as multi select picklist in visualforce page

user can select multiple picklist values in controlling field based on the selection we need to show all the dependent values in multi select picklist . For example if user selected A,B in controlling picklist then we need to show A1,A2,A3,A4,B1,B2,B3,B4 in dependent multi select picklist

Once user selects values from visualforce we need to create Trailhead record with multiple values and store in corresponding long text area fields

Create contact record by populate some data (minimum 1 fields)

Convert contact object record into XML response (Serialization) - Conversion of object into XML

Display it on page

Put a button Deserialization which needs to convert this XML into object

Create new object Candidate and store the response after parsing XML.
 

There are 3 fields on account object f1 f2 f3. f1 is inserted manually and f2 and f3 will update automatically on what event we write trigger for f2 & f3?

I am new to apex. I got above error when executing below codes of collection .Please help.

List<string> colors= new List<string>();
colors.add('Red');
colors.add('Blue');
colors.add('Blue');
system.debug('the size of the list is' + colors.size());
system.debug('the list contents are' + colors);
colors.remove(0);
system.debug('the list contents are' + colors);

Set<string> months = new Set<string>();
months.add('Jan');
months.add('Feb');
months.add('March');
system.debug('the elements in the set are' + months);
for(string st : months)
    system.debug('the elements in the set are' +st);
    months.add('Jan');
system.debug('the values in the set are' + months);
months.addall('colors');
system.debug('the added list values are' + months); 
colors.addall('months');
system.debug('the values in the List are' + colors);
system.debug('the size of the set is' + months.size());

Child to parent soql query and parent to child soql query on standard object?

why we create 2 master detail relationship per object?

How to answer this question explain 2 visual force pages of your project? can anyone help if they have done any project in visualforce and apex

Write an Apex code to find the number of tasks Assigned to a Particular contact related to an Opportunity record.

trigger Trigger4 on Account (After update) 
{
        System.debug('Total number of records in Trigger' + Trigger.size);
         
         for(account a : trigger.old)
         {
              System.debug('Account that got inserted is......' + a.name);
         }
        for(account b : trigger.new)
        {
                b.description = 'Updated by Trigger';
            System.debug('Account that got inserted is......' + b.name);
           }
             
}

Get Error on on updating any record-
Review all error messages below to correct your data.
Apex trigger Trigger4 caused an unexpected exception, contact your administrator: Trigger4: execution of AfterUpdate caused by: System.FinalException: Record is read-only: Trigger.Trigger4: line 11, column 1

And whenever try to create any new record get below error-

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger Trigger9 caused an unexpected exception, contact your administrator: Trigger9: execution of AfterInsert caused by: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, Trigger4: execution of AfterUpdate caused by: System.FinalException: Record is read-only Trigger.Trigger4: line 11, column 1: []: Trigger.Trigger9: line 13, column 1

why we create 2 master detail relationship per object?