2- The Need for Generics

Jun 20, 2026 04:39 · 3:32 · English · Whisper Turbo · 2 speakers

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Lecture Index

0:03

S… Speaker 1 (2- The Need for Generics)

Before we talk about what generics are,

0:05

S… Speaker 1 (2- The Need for Generics)

let's look at the problem they try to solve.

0:07

S… Speaker 1 (2- The Need for Generics)

So in this project,

0:09

S… Speaker 1 (2- The Need for Generics)

I'm going to add a new package,

0:11

S… Speaker 1 (2- The Need for Generics)

a new package called generics.

0:14

S… Speaker 1 (2- The Need for Generics)

I'm going to write all the code for this section inside this package.

0:17

S… Speaker 1 (2- The Need for Generics)

Now let's say we want to implement a class for storing a

0:21

S… Speaker 1 (2- The Need for Generics)

list of integers.

0:22

S… Speaker 1 (2- The Need for Generics)

So in this package,

0:23

S… Speaker 1 (2- The Need for Generics)

we add a new class called list.

0:26

S… Speaker 2 (2- The Need for Generics)

In this class,

0:29

S… Speaker 1 (2- The Need for Generics)

we need an array to store our integers.

0:31

S… Speaker 1 (2- The Need for Generics)

So let's declare a private field,

0:33

S… Speaker 1 (2- The Need for Generics)

private integer array items.

0:36

S… Speaker 1 (2- The Need for Generics)

and we set it to a new int array of 10.

0:39

S… Speaker 1 (2- The Need for Generics)

Now we shouldn't hard code the length of this array here.

0:42

S… Speaker 1 (2- The Need for Generics)

It's better to add a constructor and receive the initial capacity of this

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S… Speaker 1 (2- The Need for Generics)

array as a parameter.

0:47

S… Speaker 1 (2- The Need for Generics)

But let's not worry about this and instead implement a basic list class.

0:52

S… Speaker 1 (2- The Need for Generics)

So what is the next thing we need here?

0:54

S… Speaker 1 (2- The Need for Generics)

We need a method for adding a new integer to this list.

0:57

S… Speaker 1 (2- The Need for Generics)

So a public method,

0:59

S… Speaker 1 (2- The Need for Generics)

public void add,

1:00

S… Speaker 1 (2- The Need for Generics)

which gets an integer called item.

1:03

S… Speaker 1 (2- The Need for Generics)

Now here we also need a private field.

1:07

S… Speaker 1 (2- The Need for Generics)

for keeping track of the number of items in this list.

1:09

S… Speaker 1 (2- The Need for Generics)

So private int count.

1:11

S… Speaker 1 (2- The Need for Generics)

Now back to our add method,

1:14

S… Speaker 1 (2- The Need for Generics)

we type items of count and we set this to

1:18

S… Speaker 1 (2- The Need for Generics)

this new item.

1:19

S… Speaker 1 (2- The Need for Generics)

So initially count is 0 and we store this item at index 0.

1:23

S… Speaker 1 (2- The Need for Generics)

Now here we should increment count so next time we add an item it

1:27

S… Speaker 1 (2- The Need for Generics)

will be stored at index 1.

1:29

S… Speaker 1 (2- The Need for Generics)

Now we also need a method for getting an integer by

1:33

S… Speaker 1 (2- The Need for Generics)

its index.

1:33

S… Speaker 2 (2- The Need for Generics)

1:35

S… Speaker 1 (2- The Need for Generics)

public integer get,

1:37

S… Speaker 1 (2- The Need for Generics)

we give it an index,

1:39

S… Speaker 1 (2- The Need for Generics)

and here we return items of index.

1:43

S… Speaker 1 (2- The Need for Generics)

Now here we're not validating this index parameter,

1:46

S… Speaker 1 (2- The Need for Generics)

we're not checking to see if it's negative or greater than the number of items in

1:50

S… Speaker 1 (2- The Need for Generics)

this list.

1:51

S… Speaker 1 (2- The Need for Generics)

Let's not worry about these details and focus on an absolute basic implementation

1:55

S… Speaker 1 (2- The Need for Generics)

of a list.

1:56

S… Speaker 1 (2- The Need for Generics)

So now that we have a list,

1:58

S… Speaker 1 (2- The Need for Generics)

let's go back to our main class.

1:59

S… Speaker 1 (2- The Need for Generics)

Here we create a new list,

2:02

S… Speaker 2 (2- The Need for Generics)

new list,

2:04

S… Speaker 1 (2- The Need for Generics)

we want to import the one that is declared in this package that we just created because

2:09

S… Speaker 1 (2- The Need for Generics)

we have another class by the same name in java,

2:12

S… Speaker 1 (2- The Need for Generics)

it's declared in java .util package.

2:14

S… Speaker 1 (2- The Need for Generics)

We don't want that one.

2:15

S… Speaker 1 (2- The Need for Generics)

So, let's import our own class.

2:18

S… Speaker 2 (2- The Need for Generics)

Alright,

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S… Speaker 1 (2- The Need for Generics)

now we call the add method and insert an item in this list.

2:23

S… Speaker 2 (2- The Need for Generics)

Now,

2:24

S… Speaker 1 (2- The Need for Generics)

let's say tomorrow we want to have a list of users.

2:26

S… Speaker 2 (2- The Need for Generics)

So,

2:27

S… Speaker 1 (2- The Need for Generics)

first I'm going to add a new class in this package.

2:32

S… Speaker 1 (2- The Need for Generics)

called user.

2:33

S… Speaker 1 (2- The Need for Generics)

Now in this class we could have fields like username,

2:36

S… Speaker 1 (2- The Need for Generics)

password,

2:37

S… Speaker 1 (2- The Need for Generics)

email, and so on.

2:38

S… Speaker 1 (2- The Need for Generics)

For now, let's not worry about this.

2:39

S… Speaker 1 (2- The Need for Generics)

Instead we want to have a list of users.

2:42

S… Speaker 1 (2- The Need for Generics)

Here's the problem.

2:43

S… Speaker 1 (2- The Need for Generics)

This list that we have here,

2:45

S… Speaker 1 (2- The Need for Generics)

we cannot use this class for storing users.

2:47

S… Speaker 1 (2- The Need for Generics)

We can only store integers in this class.

2:49

S… Speaker 1 (2- The Need for Generics)

So with this approach,

2:51

S… Speaker 1 (2- The Need for Generics)

we'll have to create another class called user list,

2:55

S… Speaker 2 (2- The Need for Generics)

user list,

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S… Speaker 2 (2- The Need for Generics)

and

2:59

S… Speaker 2 (2- The Need for Generics)

In this class,

2:59

S… Speaker 1 (2- The Need for Generics)

we're going to have a user array.

3:01

S… Speaker 1 (2- The Need for Generics)

So private user array,

3:03

S… Speaker 1 (2- The Need for Generics)

let's import this type.

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S… Speaker 1 (2- The Need for Generics)

We call it items and set it to new user array

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S… Speaker 1 (2- The Need for Generics)

of 10.

3:10

S… Speaker 2 (2- The Need for Generics)

Similarly,

3:13

S… Speaker 1 (2- The Need for Generics)

we need a count field,

3:14

S… Speaker 1 (2- The Need for Generics)

so private integer count,

3:16

S… Speaker 1 (2- The Need for Generics)

then we'll have to implement our add and get methods.

3:18

S… Speaker 1 (2- The Need for Generics)

That's a lot of code duplication.

3:20

S… Speaker 1 (2- The Need for Generics)

What if in the future we want to have a list of strings?

3:23

S… Speaker 1 (2- The Need for Generics)

So this approach is very tedious and not scalable.

3:26

S… Speaker 1 (2- The Need for Generics)

In the next video,

3:27

S… Speaker 1 (2- The Need for Generics)

I'm going to show you one way to solve this problem.

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