Set is a collection of similar elements, and they are unordered. Elements can be of any data type. Set doesn't allow any duplicate values. We can't access a set element at a specific index, and we can only iterate over set elements.

Syntax:

Creating a set:

Set<DataType> variable name=new Set<DataType>();

We can assign the values statically at the time of creating a Set,

Ex:

    Set<String> name = new Set<String>{'John','Kelly','Mark'};

In another way, we can assign values dynamically when we are creating a Set,

Ex:

    Set<String> name = new Set<String>();

        name.add('John');
        name.add('Kelly');
        name.add('Mark'); 

Almost all the methods of List are similar with Set methods. Some of them are,

add(SetElement):

It inserts an element into the Set.

      Set<String> name = new Set<String>();

        name.add('cat');
        name.add('sri');

Note: If the given name matches to any of the name, which is already in the set, then only one is displayed (no duplicates).

addAll(fromlist|fromset):

It inserts list of elements or set of elements into the set.

remove(Element):

It deletes the element from the set.

removeAll(List|Set):

It removes the elements from entire list or Set.

contains(Element):

It checks whether the given element is in Set or not. If it is there it will return true. 

size():

It returns the number of Elements in the Set.

isEmpty():

It returns true if the set is empty.

Note: Above-mentioned methods are some of them and there are other methods.

Difference between List and Set:

List:

• List accepts duplicate values.
• It's an Ordered collection of data type.

Set:

• Set won't accept any kind of duplicate values.
• It's an Unordered collection of data type.

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