11- The Function Interface

Jun 29, 2026 19:39 · 3:00 · English · Whisper Turbo · 2 Oradores

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Índice de conferencias

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Let's talk about the function interface as the name implies this interface

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represents a function or an operation that takes an argument and returns

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a value So here we have two generic type parameters T

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represents the type of the argument and R represents the type of the result.

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So over here

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You can see that we have four methods in this interface.

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Three of them have an implementation.

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The only abstract method is the apply method that takes an argument

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of type T and returns a value of type R.

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Now just like the previous interfaces,

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we have a few specializations of this interface.

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For example,

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we have by function that takes two arguments and returns a

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result.

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We also have primitive specializations,

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and these specializations fall into three categories.

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In the first category,

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arguments have a specific type,

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but the return value is parameterized.

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For example,

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int function represents a function that takes a primitive integer.

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Take a look.

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For example,

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here we have the apply method that takes a primitive integer and it

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returns a value of type r.

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So,

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this is int function,

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you also have long function and double function.

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In the second category,

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the argument is parameterized.

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For example,

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to int function represents a function that returns a primitive integer.

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So over here you can see we have a method called apply as

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int, the argument is parameterized and the return value is a

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primitive integer.

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Just like this we have to long function and to double function.

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Now in the third category both the argument and the return

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type are specialized.

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For example

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into long function represents a function that takes a primitive integer and

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returns a primitive long.

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Take a look.

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So we have apply as long which takes a primitive

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integer and returns a primitive long.

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Now let me show you how to use the function interface.

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So let's declare a function that takes a string and returns an

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integer.

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So we type function of string and integer,

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we call it map

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Now we should set this to a lambda expression that takes a string and returns an

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integer.

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So let's say our parameter is str then we add the lambda operator

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and Here we just want to return the length of this string.

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So we type str dot length There's no need to add

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a code block or use the return keyword,

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okay?

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So here we have the map function now to call it

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We call it map that apply give it a string like

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sky and this returns the length of the string

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So we can print it and we get three.

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So this is how we can use the function interface in Java

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