What is Apex Class in Salesforce ?

Apex Data Types Overview

Apex supports various data types, including a data type specific to Salesforce—the sObject (Class Object) data type.

1. A primary type, such as an Integer, Double, Long, Date, Date time, String, ID, Boolean, among others.
2. An sObject, either as a generic sObject or as a specific sObject, such as an Account, Contact, or MyCustomObject__c
3. A list (or array) of primary, sObjects, user defined objects, objects created from Apex classes, or collections
4. A set of primary, sObjects, user defined objects, objects created from Apex classes, or collections
5. map from a primitive to a primitive, sObject, or collection
6. Typed list of values, also known as an enum

Apex Syntax and it's usage

Similarities between Object Oriented Programming Language (OOP) & Apex

1. Classes, interfaces, properties, and collections (including arrays).
2. Object and array notation.
3. Expressions, variables, and constants.
4. Conditional statements (if-then-else) and control flow statements (for loops and while loops).

What Apex supports in addition to Object Oriented Programming Language ?

1. Apex is stored, compiled, and executed in the cloud. (Cloud Development)
2. Triggers, which are similar to triggers in database systems.
3. Database statements that allow you to make direct database calls and query languages to query and search data.
4. Transactions and rollbacks.
5. Versioning of custom code.

Now let's check out Apex Syntax and how to use it

Variable Declaration

As mentioned earlier, Apex is strongly types language so you need to declare a variable with data type

contact cont = new contact(); 

Here Variable cont is declared as a datatype with contact (Contact is Salesforce standard object).

SOQL Query

SOQL stands for Salesforce Object Query Language and it used for fetching object from Salesforce database

Let's take an example

Contact cnt = [select id, name from Contact Limit 1]; 

This query fetches one contact records from the Salesforce database.

Loop Statement

Loop statement helps iteration over the records. The number of iterations is equivalent to the number of records in the list same as in OOP Language

For Example:

list<Contacts> contactLst = [select id, name from contact limit 100];
// iteration over the list of accounts
for(Contact cnt : contactLst){
    //you can get contact id here this way
        cnt.Id
}

Conditional Statement

When you execute some lines of code as per conditions, conditional statements are used. It is same as using If, Else If in OOP

Let's take an example

list<Account>listOfAccounts = [select id, name from account limit 100];
// execute the logic if the records returned are not empty (zero)
if(listOfAccounts.size() > 0){
    //your logic
}

Data Manipulation (DML) Statements

DML statements are used for data manipulation in the Salesforce database.

Let's take an example

Contact acc = new Account(Name = ‘ Test Account’);
Insert acc; //DML statement to create account record.

Types of Apex Access Specifiers

Apex provides the usage of the private, public, protected, and global access specifiers when defining variables or methods.

By default, a variable or method is private and only visible to the Apex code within the defining class.

You have to specify a variable as public to make it available to their classes in the same application namespace.

We can also change the visibility level by using the below access modifiers

Public

It offers access to a method, class, or variable that an Apex use within a namespace.

Private

This access specifier offers access to the method, class, and variable locally or within the code section in which it’s defined.

Protected

This access specifier provides access to a variable or method that any inner classes use within Apex class.

Global

It offers access to a method, class, or variable that an Apex use within and outside the namespace. It is a best practice not to use global keywords until required.

Keywords In Apex

Apex keywords, also known as reserved keywords, that act as a key to a code. Apex has defined these keywords as predefined words, so you can’t use them as an object name or variable as per the needs.

Below are the list of keywords in Apex

1. With Sharing Keyword
2. Without Sharing Keyword
3. Class
4. Virtual
5. Abstract
6. Interface
7. Extends
8. Implements
9. This
10. Static
11. Final
12. Super
13. Transient
14. Return
15. Null
16. Global
17. Public

What is Apex Governer Limits ?

The limits that the Apex runtime engine impose to make sure that any Apex code and processes don’t violate the processing and don’t control the shared resources for the other users on the multitenant environment

Such limits are authenticated against apex transactions.

Salesforce has defined various governor limits on every apex transaction, like

For SOQL queries that can be done in a synchronous transaction - Max Query Limit is 100
For SOQL queries that can be done in an Asynchronous transaction, etc. - Max Query Limit is 200

How to create an Apex Class in Salesforce?

1) Click on Setup Icon available in right hand side of page in Lightening

2) Enter Apex Classes in the quick find Box, then Click on Apex Classes

3) Click on New button present in Apex Classes Page, then you will see the window to add Apex Class Code