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We know how bigger and instance variables are declared or initialized.

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However Djala also provides a facility called initialiser block which can be useful for initializing

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tactic instance variables in certain situations.

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There are separate initialiser rocks for instance variables.

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And let's see what they are.

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Let's just look at static initializer.

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It can be useful to initialize static fields that cannot be initialized in a single line.

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That is you need multiple lines to initialize them and here are two good use cases.

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First one is about populating a data structure.

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Well second one is about having some error handling code if initialization leads to any errors.

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Let's look at examples for these two use cases in this example.

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We are creating an instance of hash map which is a data structure that we will review later but it is

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basically a hash table implementation that stores a collection of key value pairs.

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Example would be starting a persons name esky and his or her phone number as a value.

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It wouldn't help us to search for a person's phone number given his or her name.

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So here we are first creating a hash map object which is referenced by a static variable.

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Now if you want this hash map to be populated with some data before it is used anywhere in the class

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then a good way to do it would be to use a static initializer block that is you would populate the data

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inside the static initializer block as we can see here the starting condition as a block involves the

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keyword static followed by opening and closing lists and in between the two phrases we have the statements

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populating the hash map.

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As you can see we're adding the key and value pairs in each statement.

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So the starting condition is that block is helping us to completely initialize the hash map as it could

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not be done in a single line.

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When I say completely I mean even populating the hash map with this no any code in the class can use

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the popular hash map.

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Here is another example.

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Let's say there is a static variable called stuff and it is initialized by the value written by this

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method called Get Stuff No get out of control an exception and exceptions will be covered later.

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But as we mentioned earlier it is basically an error.

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And we may have to handle it when it is connected.

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Destroy catch but that you see here is used for catching exceptions and handling them and certainly

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the exception handling Guard can go into this catch block.

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Not without a static initializer.

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It wouldn't be possible to have this initialization statement and grossly in a quick catch block directly

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within the class.

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That is we get a compiler error.

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So static initializer is permitting us to do this.

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Alternatively we can use a private static method as shown here.

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Here the static variable is initialized been in rockish an affair.

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But I read static method that one did of this approach is that we can always re-initialize the start

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degradable by simply invoking this method.

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We cannot know how any number of static initializers and they will be executed in the order in which

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they appear in the source code.

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Like static matters Cordone search static initializer cannot reference instance members like Instance

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variables are instance methods and that's about static initializers.

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Let's look at instance initializers an instance initializer basically initializes instance variables

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.

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And here is the syntax.

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It is same as static initializer but not start a keyword.

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But we know the constructors initialized it.

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Then why do we need instance initializers.

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It is useful when sharing a block of code between multiple constructors.

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What it means is that under the hood the Java compiler copies initialiser Brockes in the beginning of

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every constructor.

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And without this feature you would have to manually copy the same code in each constructor.

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Let's quickly try this out in code.

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Ok here is the basics demarc class.

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So let's just go ahead.

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I had an instance initializer here.

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Let's just have a print statement.

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Let's just print the statement inside an instance initializer

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.

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Now let's also add a constructor

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.

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And this Conard has no our constructor.

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Let's add one more constructor that some fake parameter ID and purchase say inside constructor regret

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barometer.

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OK let's simply invoke create an instance of BASIX them or just call it bt where the new is X Nemo.

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So let's just compile run it so as you can see it says inside instance initializer and then it says

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inside nor constructor.

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That's because we are invoking the constructor here.

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And as you can see the instance initializer code has been copied to the beginning of the constructor

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and it also appears after the constructor so it doesn't make any difference so it's just going to copy

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this into this matter into the into the constructor into the beginning of the constructor.

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Now let's just pass a value on here so that we are invoking the second constructor and so that to compile

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once again.

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And let's just run it.

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So now as expectorate is inside instance initializer and then it also says inside constructor with a

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parameter.

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So once again the instance initializer has been copied to this to the beginning of the second constructor

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.

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So basically instance initializer code will always be copied to the beginning of each of the constructors

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.

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So that's the main use and we have seen it here in code and that's about it.

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No like in the case of static initializers we cannot also how any number of instance initializers and

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there will also be executor in the order in which they appear like instance Medders instance initializers

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can also reference static members and that's about it.

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We'll look at buttstock an instance initializer groks static initializers Grogs Halvard initialization

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of static variables is not possible in a single line instance initializer.

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Blocks can be used when multiple constructors have some common initialization called and that's about

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it.

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Thank you