4- Lambda Expressions

Jun 26, 2026 23:13 · 3:43 · English · Whisper Turbo · 2 Konekte

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So our greet method talks to the printer interface,

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and this is a functional interface because it has a single

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abstract method.

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Now,

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wouldn't it be nice if we could implement this method in a standalone function,

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like a function that exists on its own without belonging to a class.

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That is what lambda expressions are for.

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So a lambda expression is like an anonymous function that we can pass around.

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Let me show you.

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So I'm going to rewrite this code using a lambda expression.

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First recall,

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the greet method.

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Now here we want to pass an implementation of the print method as

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an anonymous function.

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So this print method has a

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single parameter of type string.

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Let's add that over here.

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This is where we list our parameters.

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So string message.

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After parenthesis,

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we add an arrow.

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This is called the lambda operator.

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And then we add braces to represent the body of this

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function.

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Now,

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what should we do here?

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We should add a print statement and print this message on the

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console. What we have over here is called a lambda expression.

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So if you have a functional interface,

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we can represent this functional interface using a lambda expression.

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That is why these interfaces are called functional,

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because they represent a function.

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So here we have a lambda expression.

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As you can see,

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this code is very clean and concise,

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but we can make it better.

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First of all,

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we can remove the type of this parameter.

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Now, the Java compiler knows that this parameter is a string object

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because the lambda expression that we pass over here will be checked against

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the signature of the print method.

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So the Java compiler knows that this method has a single parameter and

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the type of this parameter is string.

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So we don't have to repeat that type over here.

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If I type message dot,

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now you can see all the string methods.

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By the same token,

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if I add another parameter here,

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The Java compiler complains because it knows that our print method has

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a single parameter,

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but here we're passing two parameters.

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Okay, so for the most part,

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we can exclude the type of parameters and let the Java compiler infer them.

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Now,

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if you have a single parameter,

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we can also remove this parenthesis.

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That makes our code cleaner and more concise.

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We use parenthesis only if we have no parameters or

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if you have a method with multiple parameters.

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So we separate these parameters using a comma,

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just like how we declare the parameters of a method,

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okay?

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So here we have a single parameter,

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and we don't need parentheses.

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Also,

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if the body of this function has a single line of code,

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we don't need these braces either.

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So I can clean up this code by pressing alt and enter,

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and selecting replace with expression lambda.

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There you go.

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So this lambda expression looks really clean and concise.

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Compare this with an anonymous inner class.

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This is really ugly.

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So let me remove this.

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Alright,

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now here we're passing a lambda expression as an argument to a method,

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but we can also store a lambda expression in a variable.

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For example,

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we can declare a variable of type printer and set

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it to a new console printer.

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So this is the concrete implementation or we can set this

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to a lambda expression.

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So here we say message goes to print message.

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So lambda expressions are essentially objects,

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but we can use them to represent anonymous functions.

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