To achieve this requirement, we will be using two Chatter objects viz. Feed Item and Feed Comment. ‘Feed Item’ records are the posts created by a User and the ‘Feed Comment’ records are the comments on that post.

In other words, our requirement is to insert a random ‘Feed Comment’ record, whenever a ‘Feed Item’ record is inserted.

The Trigger should be written with the following flow:

1. Define the Trigger
2. Create a list for DML (last step)
3. Create a List of ‘Strings’/ Comments
4. Get a Random comment from the List in Step 3
5. Iterate through each Feed Item record in the List from Step 2. and add the random comment.
6. DML to insert List of newly created records

Now lets go through each step once again and write its respective code.

trigger randomChatterComment on FeedItem (after insert) {

    //Create a list to hold the list of Feed Comment records being inserted
    List<FeedComment> List2insert = New list<FeedComment>();

//Create a list of Strings
    List<String> commentList = New List<String>{
        'Congratulations and BRAVO!',
            'This calls for celebrating! Congratulations!',
            'You did it! So proud of you!',
            'I knew it was only a matter of time. Well done!',
            'Congratulations on your well-deserved success.',
            'Heartfelt congratulations to you.',
            'Warmest congratulations on your achievement.',
            'Congratulations and best wishes for your next adventure!',
            'So pleased to see you accomplishing great things.',
            'Feeling so much joy for you today. What an impressive achievement!',
            'You’ve worked so hard for this. Congrats!',
            'This is awesome! You’re awesome! Way to go!',
            'Here’s to your streak! Keep it up!',
            'Sincere congratulations on your hard-earned success',
            'You are proof that good things come to those who are willing to sacrifice to reach a worthwhile goal. Words can’t express how proud I am!',
            'You have the creativity and determination to do whatever you can dream. I hope you feel proud today and confident in your ability to rise to your next challenge.',
            'Celebrating the dedication you’ve shown on the way to this achievement. You’ve earned every bit of the success you’re enjoying.',
            'Congrats!!!'           
            };

//Get a random number which is less than the size of the above list
   Integer i = (Math.random()* (commentList.size() -1)).intvalue();

    //iterate through each feed item record and add the comments
    For (FeedItem FIR:Trigger.new) { 
        //check if the post contains the word "Success"
        If (FIR.Body.contains('success')) {
            FeedComment FC = New FeedComment(); 
            FC.CommentBody = commentList.get(i);//add a random comment from the comment list using the random number generated earlier
            FC.FeedItemID = FIR.id;
            FC.CreatedById = '005f4000002NG0g'; //ID of user who will be commenting
            List2insert.add(fc); //add to final list of comments that needs to be inserted
        }
    }

Insert List2insert; // insert the final list of comments

The complete trigger to post a random chatter comment will be as follows:

trigger randomChatterComment on FeedItem (after insert) {
    
    //Create a list to hold the list of Feed Comment records being inserted
    List<FeedComment> List2insert = New list<FeedComment>();
    
    //Create a list of comments
    List<String> commentList = New List<String>{
        'Congratulations and BRAVO!',
            'This calls for celebrating! Congratulations!',
            'You did it! So proud of you!',
            'I knew it was only a matter of time. Well done!',
            'Congratulations on your well-deserved success.',
            'Heartfelt congratulations to you.',
            'Warmest congratulations on your achievement.',
            'Congratulations and best wishes for your next adventure!',
            'So pleased to see you accomplishing great things.',
            'Feeling so much joy for you today. What an impressive achievement!',
            'You’ve worked so hard for this. Congrats!',
            'This is awesome! You’re awesome! Way to go!',
            'Here’s to your streak! Keep it up!',
            'Sincere congratulations on your hard-earned success',
            'You are proof that good things come to those who are willing to sacrifice to reach a worthwhile goal. Words can’t express how proud I am!',
            'You have the creativity and determination to do whatever you can dream. I hope you feel proud today and confident in your ability to rise to your next challenge.',
            'Celebrating the dedication you’ve shown on the way to this achievement. You’ve earned every bit of the success you’re enjoying.',
            'Congrats!!!'           
            };
                //Get a random number which is less than the size of the above list
                Integer i = (Math.random()* (commentList.size() -1)).intvalue();
    
    //iterate through each feed item record and add the comments
    For (FeedItem FIR:trigger.new) { 
        //check if the post contains the word "Success"
        If (FIR.Body.contains('success')) {
            FeedComment FC = New FeedComment(); 
            FC.CommentBody = commentList.get(i);//add a random comment from the comment list using the random number generated earlier
            FC.FeedItemID = FIR.id;
            FC.CreatedById = '005f4000002NG0g'; //ID of user who will be commenting
            List2insert.add(fc); //add to final list of comments that needs to be inserted
        }
    }
    Insert List2insert; // insert the final list of comments
    
}

Requirement: Write a Salesforce Apex Trigger to create a Task when an Opportunity is updated. The task should be assigned to the Opportunity owner and the status of the task should be “In Progress”.

The Salesforce Apex Trigger Sytax is as follows:

trigger *triggerName* on *Object* (*before/after event*) {
    for (*Object* *Variable* : Trigger.New)      
        **Trigger Actions & Code Block**
}

Now lets write our trigger with the following steps.

1.  Define the trigger
2.  Iterate through each opportunity
3.  Create a Task
4.  Assign values to the Task

trigger createTaskOnOpp on Opportunity (before update) {

for (Opportunity Opp :Trigger.New) {

Task t = new Task();

	t.WhatID = Opp.Id;
	t.Ownerid = opp.Ownerid;
	t.subject = 'This is the Subject';
	t.Status = 'In Progress';
	t.Description = 'This is the Description';
	insert t;
	}
}

The complete Salesforce Apex Trigger to create a Task when an Opportunity is updated would be:

////define the trigger name, object and events
trigger createTaskOnOpp on Opportunity (before update) {
    //Iterate through each opportunity and assign it the variable Opp
    for (Opportunity Opp :Trigger.New) {
	//Create a new task and assign it the variable t
        Task t = new Task();
        // Assign Values to the task t
        t.WhatID          = Opp.Id;
        t.Ownerid         = opp.Ownerid;
        t.subject 	  = 'This is the Subject';
        t.Status	  = 'In Progress';
        t.Description     = 'This is the Description';
        insert t;
    }
}

This is how the trigger looks in the developer console (image)

The “Hello World” program is the simplest program used to illustrate the basic syntax of a programming language. The program outputs “Hello World” and is traditionally the first program written by all beginner developers.

Let’s write our first “Hello World” Salesforce Apex trigger which will update a Lead with “Hello” as the first name and “World” as the last name.

Requirement:
When a Lead is updated, update the lead’s first name to ‘Hello’ and last name to ‘World’

Lets write the trigger in the “Developer Console”. To access the developer console, click the drop down on your Name (on the top right), and then click on Developer Console.

Once the developer console is open, click on File >> Open >> Apex Trigger. Now we are ready to write our first trigger.

The Trigger Syntax:
Every trigger is defined by using the following syntax:

  trigger *triggerName* on *Object* (*before/after event*) {
       for (*Object* *Variable* : Trigger.New)
       **Trigger Actions & Code Block**
  }

Here is what the terms in the syntax mean:

• ‘triggerName’ is the name of the trigger which describes it.
• ‘Object’ is the name of the Object on which the trigger is created
• ‘before/after event’ are a comma separated list of events like insert, update, delete
• ‘Trigger.New’ is a list of sObject records
• ‘Variable’ denote a piece of memory that can contain a data value. Descriptive text is used as variables.

Lets get back to our requirement and based on the above syntax, write our ‘Hello World’ Salesforce Apex trigger.
Remember, when a Lead is updated, the first name should be updated to “Hello” and the Last Name to “World“.

We will be using comments to describe the lines of code in our trigger. But what are comments? Comments are used to describe code and are ignored by the parser – meaning the comments are NOT treated as code and will not run.
Single line comments are preceded by // and multi line comments are wrapped in /* and */

Now here comes the trigger:

// Name of the trigger is HelloWorld, It is on the Lead Object and It will run before the lead is updated (event).
trigger HelloWorld on Lead (before update) {
        //for every lead record, denoted by variable ld,in the list that is being updated
        for (lead ld : Trigger.new) {
             // add the first name as 'Hello'
             ld.FirstName = 'Hello';
             // add the last name as 'World'
             ld.LastName = 'World';
         }
}

This is how it looks in the developer console.

Exercise to get used to the syntax and the basic trigger for beginners:

Write a trigger to update the first name of the contact as Taha and the last name as Syed and the Phone number as 000-111-9999