9- Chaining Consumer

Jun 29, 2026 19:22 · 4:28 · English · Whisper Turbo · 2 Speakers

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Lærarabókin

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S… Speaker 1 (9- Chaining Consumer)

Earlier I briefly mentioned that the consumer interface has a default method called

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and then.

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With this method we can chain consumers which basically means we

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can run many operations in sequence.

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Let me show you how cool and powerful this is.

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So I'm going to create a list of strings and

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initialize it using list of.

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Here I'm going to pass three strings like a,

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and c.

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Now you learn that the consumer interface represents an operation that takes

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a single argument and doesn't return a value.

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So let's declare a variable of type consumer of

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string.

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I'm going to call this print.

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Now we should set this to a lambda expression.

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This lambda expression should match this method.

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So it should have a parameter of type string and it shouldn't

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return a value.

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So here we add string item goes

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Let's just print this item.

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Now once again,

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we can simplify this lambda expression by removing this type because

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the Java compiler knows that here we're consuming a string.

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So the item that we pass here is a string object.

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So there's no need to explicitly specify the type.

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Now because we have a single parameter,

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we can get rid of the parentheses.

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That is better.

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So here we're declaring an operation called

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print that takes an item and prints it on a terminal.

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Now let's declare another operation that prints a string in uppercase.

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S… Speaker 2 (9- Chaining Consumer)

So,

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once again,

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consumer of string,

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we call it print uppercase.

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Pay attention to how I'm naming these consumers.

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The name of this variable clearly represents this operation.

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So,

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once again,

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item goes to,

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you want to print this,

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but first we want to convert it to uppercase.

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Pretty straightforward,

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right?

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Now,

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we want to iterate over this list,

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and for each item,

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we want to execute these two operations in sequence.

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So we call list .foreach.

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S… Speaker 1 (9- Chaining Consumer)

Here we should pass a consumer object,

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so I'm going to pass print,

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now this consumer has a method called and then.

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Now look at the parameter of this method.

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Here we can pass a second consumer.

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So we can pass print uppercase.

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Now, when I run this program,

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you'll see that for each item,

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first we're going to print that item and then we're going to print it in uppercase.

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Take a look.

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S… Speaker 2 (9- Chaining Consumer)

There you go.

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That's pretty cool.

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Well,

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let me explain how the magic happens under the hood.

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So I'm going to put the caret on the method name and then,

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now on the top,

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if you go to the navigate menu,

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look at the shortcut for declaration.

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On Mac,

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it's command and B.

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On Windows,

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it's probably control and B.

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So I'm going to press command and B.

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Now you can see the source code of this method.

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So let's see what's happening here.

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This method takes a consumer object called after.

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First,

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it ensures that this argument is not null.

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Pretty straightforward.

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Now,

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look at what is returned here.

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We're returning a lambda expression.

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This lambda expression represents a consumer object.

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So it takes an argument of type T

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And in the body of this lambda,

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first we call the accept method of the current consumer.

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So we're executing the current operation and then we're

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calling the accept method of the second consumer.

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This is how two operations get executed sequentially.

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So every time we call this method,

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we get a new consumer.

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And that means once again we can call and then on that new consumer

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to chain another task.

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Let me show you.

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Back to our demo once we call and then we get

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a new consumer object So here we can call and then and then

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pass another consumer object like print So with

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this code we're executing three operations in sequence

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Look at the result.

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There you go.

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We're printing each item three times on the terminal So

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this is how we can chain consumers

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