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Hello.

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Students, in this lesson, we're going to learn what consumer by consumer product and by product interfaces

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are as usual.

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We'll start from an investigation of a source code of all interfaces.

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We'll review all matters that are defined there.

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One real example will show you how you can use these types and how to implement LAMDA functions and

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methods, references to implement consumer by consumer product and by product types.

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After that, we'll talk about two other types.

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We are also going to default and static methods from these interfaces.

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We have a lot of things to learn today.

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Let's start.

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The best way to learn this topic is to investigate the source code and the real examples.

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I suggest starting our lesson today from the overview of consumer interface source code.

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As you can see, similar to other types declared in Geritol function package consumer is a functional

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interface that has one abstract method with a name, except it takes some argument and returns nothing.

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So this type exists to perform an operation on the given argument, unlike other functions.

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This type of function usually produces side effect.

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I'm talking about that.

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The reason to use this type is to modify the state of the argument and create a function for that.

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This interface also has one default method.

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This is and then Masset, in the previous lesson we learned how we can use and then MassArt to compose

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new function on the basis of two other functions.

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It works the same way with consumer.

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That's why it will not pay a lot of attention to this method.

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Take into account we reviewed it in previous lesson, but instead I will show you examples of consumer

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unpracticed.

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I prepared real life example for you that will help you to grasp new knowledge faster.

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I will leave the link to this file in the lesson attachments.

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Imagine that you have a list of products.

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This is product type that we used for some of the home tasks.

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While we are in collections, let me remind you how it looks like this typesetters contract that allows

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us to retrieve Idy product, name, category, name of each product and set price if needed.

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In our example, we will use default product type that implements product interface NASSAN special in

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the source code of default.

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Product type just data was getters and setters.

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And our example.

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I created a few test products.

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I passed the constructor iji product name, category, name and price.

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Hobbs's is clear for you.

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Now imagine that I want to give possibility for administrator to increase price of products.

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For example, administrator could select the specific products.

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Those products will be grouped in the least object on the backend and price will be increased for each

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product from this list by amount of money set by admin.

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Here, a graded method increase price for product list that takes as arguments and list of products

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and specific amount of dollars to increase price and a massive body attack.

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Iterator of my product list and call for each method.

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Let me open the source code of this method to explore it together with you.

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As you can see, this is the default method declared in iterator type.

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It takes consumer as an argument in simple words.

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It takes some actions.

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It has to be performed with each element remained in this iterator.

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You can see that we have while loop here and accept method of consumer is invoked for each element from

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this iterator.

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Now let's get back to our demo file and we will implement lambda function for our consumer.

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Here you can see the anonymous function that takes one argument and that returns nassan.

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I call set price Masset on each product and set the result of radiation of current price and local variables

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that passed to the Massett.

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And then my program.

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I can call this method and pass the list of products an amount of money to increase price.

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After that, let me print each product from the new line.

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I ran the program here.

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You can see in console output that price is increased by ten dollars for each product.

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Can you understand now how we modified state for all products in connection with the help of consumer

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that we passed two for each remaining MassArt?

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Hope it makes sense, by the way, I believe from the previous Lasley already understood that this lambda

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function is interchangeable with MassArt reference.

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Please let me know in case there are any questions.

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When you understood how consumer works, let me show you how my consumer works.

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I open source code of BI consumer interface.

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We learned with you specifics of naming convention individual function package during the previous lesson.

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Now you can understand that this by prefix is associated with the Arati of accept function.

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You can see that accept takes two arguments and returns nassan.

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This interface also declares one default Masset, and then that is similar to other interfaces from

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this package to compose new functions on the basis of already existing functions.

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Now, I want to get back to our demo file to show you an example for our next demo.

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I created an object of type hash map.

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It is parametrized by integer and product type imagines a similar case.

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I have product ideas that are mapped against the products and I want to have opportunity to update each

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entry in map for that purpose.

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I have created increased price for product map method, the text map of ideas and products and price

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to increase.

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Here you can see that I call for each method on my map object and pass by consumers there.

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Here's lambda function that takes two arguments and returns.

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Nassan, in case I don't need to modify key, I just ignore it.

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And you can see the body of this function is similar to the previous one.

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The only difference here is that I have access to the key in case I need it.

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Now, in my program I can call the method and parse, map, object and price to increase.

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After that we print each product from new line in console and then cancel output.

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You can see that price is increased knowing the difference between consumer and by consumer.

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You can use either of these types during the development.

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Also, you saw how to investigate the matter signature to understand what type is expected.

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Usually it is obvious what will be passed to the function as arguments, but in case it is not clear,

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you can investigate the source code of matter that requires function.

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One of the goals of this course is not to teach you all possible things, but to teach you how you can

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learn these things by yourself.

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Let me show you how you can understand what values will be passed to the anonymous function during the

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runtime.

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For example, I open the source code for each method in map type.

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The first thing I want to know is where access method is invoked on the buy consumer argument.

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Here is MassArt invocation and I see that K and V variables are passed.

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But what object stands behind K and V variable based on the variables name?

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It is clear what key and value are referencing to.

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But just in case we can check it, few lines above we can see that K variable is initialized with key

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value on each iteration and variable is initialized with the mapped value.

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You can see that operation is performed for each entry.

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That's how you can easily understand what values will be passed to the function.

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OK, now when we learned consumer and by consumer types, I want to learn with your predicate and by

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predicate types.

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I believe that knowledge of Lambda functions and Massata references will help us to learn predicate

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type faster.

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Let me open the source code of Predicate Interface.

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Prickett has one abstract method with the name test.

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This method takes an argument and returns.

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Boolean value is a true or false in stream API.

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Predicates are used very often to filter values and remove elements.

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For example, to help you understand how it works.

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Let me show you a simple example.

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For pre-cut example, I created a separate file.

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I will also leave link to this file in attachments.

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Does lesson.

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Imagine that you have a list of products here.

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You can see product list that are similar to one we have in consumer demo file and we have to remove

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all products from this list that have price more than you specified to this requirement I created to

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remove products if prices more than Massett.

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That takes a list of products and price as arguments on my list object I call remove if MassArt let

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me open source code of this method.

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As you can see, this method is from collection interface and it takes Birckhead as an argument.

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Test method will be invoked for each element in this list and in case that Masset will return true,

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then this element will be removed.

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Based on this, we can make a conclusion that we need to write a function that will return true for

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elements that must be removed.

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Is it clear now let's get back to our demo file.

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I wrote function here as it returns.

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True, in case product price is more than price value that was passed to this method.

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And in my program I call the new method and pass list of products and one hundred.

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That means that all products that have price more than one hundred will be removed.

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We can see that I have only one product with price more than one hundred.

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That's why when I print all product to console from the new line here, I still expect to see the rest

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two products.

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Let me run the program by some console output.

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We can make a conclusion that product with price more than one hundred.

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Was removed from my list.

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Awesome.

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Now let's investigate the default and static methods from project interface it has and method that allows

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us to compose two functions and add additional predicate.

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This gives us a similar flexibility that we learned in lesson about functions when we combine different

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functions.

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Let me show you the next example in the source code.

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Imagine that I need to remove all products that have price more than some specific value and category

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name is Category one and create a Masset where I create two functions.

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The first one is already familiar to you.

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That function is to test the price and the second function checks category.

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And when I call remove if MassArt, I create the new function that is returned as a result of and Masset

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invocation.

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I combine these two predicates now aliment will be removed only in case requirements of two predicates

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will be met.

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In my program I pass list of products, price and category one name.

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Based on the current state of my product list, I can see that only one product will be removed after

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the Macit invocation product with i.e. one has price more than 90 and category name is equal to category

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one.

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And in console output you can see that the product was a new one was removed.

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And I want you to understand that you're going to compose multiple predicates together, not only to

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but even more if you need.

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That will allow you to create customized predicates, one that will be needed in case we want to compose

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predicates to receive predicate that will return.

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True, in case we meet the requirements of at least one predicate of combined ones that we need to use

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default or method from predicate interface.

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I believe that is logical and clear and does not require any additional demo.

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The next default method and predicate interface is negate it returns logical negation of the current

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predicate.

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Is it clear?

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Let me show you this on example.

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In case in our previous example I would call Negate Masset, the result would be opposite.

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That means in case this function returns true, as a result, the force will be returned after negation.

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Let me call negate method here and run program one more time.

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And in console output you can see that product with ADC was removed.

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So the product that is less than 90 and the product that has category names that is not equal to Category

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one was removed.

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Can you understand now what it is?

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If yes, then let's proceed.

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We have two more static methods.

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Here is equal.

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MassArt returns use a predicate that will check if two arguments are equal to make sure that predicate

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will work as expected, we need to check that equal Masset in the type that we want to use for comparison

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is overeaten.

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This is needed because for comparison will be used objects equal MassArt and the second method is not.

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That takes expected as an argument.

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This method negates the result of the supplied predicate.

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You can see that this is achieved by using the call of Landgate method inside.

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So technically you can use is an agreed method in case you have variable of type predicate.

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Like I showed you an example, one in case you don't have variable of type predicate you can call predicate,

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not method and pos lambda function.

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Here to help you understand these two masses, let me show you an example in our perfect demo file.

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We have one more example at the bottom here.

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Imagine that we have a list of users I use user for hash tables type that implements user interface.

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I use exactly Zeze implementation because it as equals Masset overridden.

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We added a few users to the list.

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You can see user i.e. first name, last name, password and email.

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That's just for the sake of example.

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And according to business requirements, I have to be able to filter the list of users to leave their

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only user that I need here.

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I created a user object that will be used during filtering.

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I call remove if MassArt on my list of users and I call Predicate is equal method here.

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But in case I would call just this method, I will get protocols that will remove only user that equals

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to this one.

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I need exactly the opposite.

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I need to keep only this user.

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That's why I have to use negation here.

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And technically I could call negate method here, but also I can pass this packet to static method not

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is it clear.

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And when I print the list of users to cancel, I see that I have only users that I wanted to keep in

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the list also now you know.

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All matters from PAGAD interface and the very last things that I wanted to discuss with you is my predicate

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interface.

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I believe you already understood how pre-cut works.

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The only difference is that test Masset takes.

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Two arguments here will use this method when we all stream API.

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But the principle of writing and using by predicate is similar to examples that we saw with predicate

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beside.

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One abstract matter of this interface also has three more default methods Ziya and negate and or methods.

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We have just reviewed similar message from pre-record interface.

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That's why I think that there is no need to review examples with these methods.

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But let me know in case you have any questions.

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That's all what I wanted to share with you today.

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Now let's recap what we have learned today.

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Today we learned with your consumer and by consumer interfaces and real examples, you saw how you can

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create LAMDA functions for these types.

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After that, we learned precut interface nuance.

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All mascot's from pre-record interface and had practice exercises with this type.

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And at the end of the lesson we talked about biproduct interface.

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That's all for this lesson.

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Thanks a lot for your attention.

233
00:16:20,810 --> 00:16:22,400
See you in the next lesson.