11- The Set Interface

Jun 21, 2026 10:34 · 5:33 · English · Whisper Turbo · 2 غږوونکي

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Now let's talk about the set interface.

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This interface represents a collection that contains no duplicates.

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So it's a great way for storing a list of unique values.

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Let me show you.

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So here I'm going to declare a variable of type set of string.

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Let's import this.

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And we set this to a new hash set.

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This is one of the implementations of the set interface that you use 90 %

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of the time.

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Now we can add a few items to this set.

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So set .add,

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I'm going to add sky.

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then is blue.

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Now I want to duplicate this line so we have two blues.

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Let's see what happens when we print the set.

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The duplicate

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is gone.

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But look at the order of items.

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We have sky blue is.

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So the set interface does not guarantee the order of items.

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That is one of the important characteristics of the set interface you need to understand.

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Do not rely on the order.

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A set only guarantees the uniqueness.

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Okay?

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Now, let's say we have a collection of items and we want to remove the duplicates.

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Using a set,

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we can do it in one line.

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Let me show you.

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So I'm going to delete all this code.

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Let's create a collection

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of string,

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call it collection,

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and set it to a new array list.

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Now in this collection,

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we want to add a few items.

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So I'm going to use the collections class and call

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the addAll method.

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Here we pass our collection along with a

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few strings.

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A, B,

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C and C.

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So we have duplicates.

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Now we can remove the duplicates by only one line of code.

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So all we have to do is to put this collection in a set.

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So we declare a set of string and

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set it to a new high set.

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Now look at the parameters of the constructor of the high set class.

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So this constructor is overloaded three times.

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Look at this overload.

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here we can pass a collection of unknown extends string.

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So once again,

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we have a wild card here and that means we can pass a collection of string or

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any type that extends the collection interface.

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For example,

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we can pass a list of string or a queue of string or another

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set.

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So I'm going to pass our collection over here and

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now if we print the set,

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you can see that the duplicates

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are gone.

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So that's a very cool technique.

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All we have to do is to put a list or a collection inside a set and

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the duplicates are gone.

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Now,

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let's talk about the set operations.

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So I want to create a new set,

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set of string,

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let's call it set one.

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Here we set this to a new high set.

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Now,

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this time instead of a collection,

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I want to pass a list of string.

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But we don't have a list yet.

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One way is to create a list over here.

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But I'm going to show you a better way,

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a faster way.

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We have this class called arrays.

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This is also declared in the java .util package.

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This class has a static method as list.

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Now look at the parameter of this method.

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We have string dot dot dot.

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As I told you before,

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this is called var args,

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which represents a variable number of arguments.

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So here we can pass zero or more arguments.

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I'm going to pass three items,

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a, b,

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and c.

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So this method will return a list of strings initialized with

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these three items.

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Okay, let me put this on a new line so we

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can see clearly, that is better.

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Now I'm going to create another set but with different

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items.

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So B,

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and D.

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And we're going to call this set 2.

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Now when it comes to sets,

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there are four operations that you need to understand.

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One of them is the union operation,

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which is the combination of two sets.

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So if I want to combine these two sets,

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I can write set one dot add all.

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Now look at this parameter.

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It's a collection of string.

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Here we have a wildcard,

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so we can pass a list of string,

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a set of string,

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or a queue of string.

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So we can add set two,

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and now if we print set one,

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You can see that it has all the items in both sets without any

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duplicates.

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So this is the union operation.

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Another useful operation

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is intersection.

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And that will give us the items that are common in both sets.

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To get the intersection,

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we call the retain all method.

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So this method will retain or keep all the items in set two and

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remove everything else from set one.

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Take a look.

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So the intersection of these two sets is B and C.

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Another useful operation is difference.

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You want to know what items we have

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in the first set that we do not have in the second set.

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To do that we call the remove all method.

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So we are removing everything that we have in set two and keeping the rest.

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Take a look.

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So the result

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is A.

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So this is how we can use sets.

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In the next video we're going to talk about maps.

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