Apex Basics and Collections Q&A

1. What are the OOPS Concepts?

Any language which supports the following concepts are called OOPs based languages.

  • Encapsulation – Class and Interface – a way to bundle data and capabilities to operate on that data.
  • Abstraction – providing the appropriate level of information and data at the requested level, with the help of access specifiers (i.e. private, protected, public and global)
  • Polymorphism – it allows you to define ways of dealing with data without knowing exactly how that data will be defined in the future.
  • Inheritance – the capability of a class or object to have certain methods and attributes passed down to them through a hierarchy, this we will achieve by using extends and implements keywords.Apex supports all the above mentioned concepts so Apex is OOPs based language.
  • Note: Apex is Case Insensitive.
2.What is the difference between non-static and static?
  • By default all the variables and methods are non-static.
  • Scope of the non-static variables or methods is within the scope of the same object.
  • We can declare variables and methods as static by using static keyword.
  • Scope of the static variables and methods is throughout the transaction.
  • Static variables and methods, we can directly call with class name (we cannot access static variables and methods with object name).
3.What are the types of Collections available in Apex?
  • List – ordered and allow duplicates
  • Set – unordered and won’t allow duplicates
  • Map – Key and value pair
4. What is the difference between List and Set?
1 Ordered Unordered
2 Allows duplicates Doesn’t allow duplicates
3 Can access elements with index Cannot be accessed with index
4 We can sort list elements with sort method – default sorting order is ascending Sort method is not available
5 Contains method is not available Contains method is available, to search for a particular element
6 Can process records which are stored in list using DML statements (insert, update, delete and undelete) Cannot process records which are stored in set using DML statement
5.What is the maximum size of the list?

No limit for the size of a list. It only depends on the heap size which is 6 MB (Synchronous) and 12 MB (Asynchronous).

6.What are the map methods available in Apex?

Map holds key and value pair. Map keys are case-sensitive.


Map<Datatype, Datatype> mapName = new Map<Datatype, Datatype> ();

keyset(): To fetch only keys from the map.

values(): To fetch only values from the map.

containsKey(value): To search a key from the map.

get(key): By supplying the key we can fetch the value.

put(key,value): To add key and value in a map.

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