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Not let's look at constant variables we briefly look at them while discussing such statements.

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Let's not look at them in a more formal way.

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We know that variables are evaluated at runtime or not compile time Hollywood constant variables are

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a kind of final variables whose values are known at compile time X and that is we don't have to wait

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until runtime to know their values.

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For this reason they're usually also referred to as compile time constants.

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And here is one example.

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It is variable pipe from the math class.

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The benefit of knowing the value at compile time is that the compiler can take that value and replace

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every instance of the variable with the actual value itself.

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And this element in some runtime or heard for example here we have the variable x which is assigned

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my doc by but my doc is a compile time constraint and the compiler knows the corresponding value 3.1

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for services 3.1 for directly to the variable x and store it in the class file as part of the bike.

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So this Elements need some overhead at runtime as Debian doesn't have to look into the math class to

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make this assignment.

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So compiler is able to perform such an optimization.

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So basically constant Fribbles are final variables but for a final variable to be qualified as a constant

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variable there are few restrictions on that look at them.

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First is obviously it needs to be declared with a modifier final.

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Next did different type of variable should be either a Plimmer or a string.

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If you have any other the debate then it will not be a constant variable.

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Next a variable must be initialized in the declaration statement itself.

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That is it cannot be initialized somewhere else like in a constructor or in some initial as a block

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.

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Finally the initialization expression itself which is on the right side of the assignment must be a

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constant expression a constant expression is something whose value is known at compile time itself and

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hence it is also referred to as compile time constant expression.

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There are some rules on glauca expressions qualify as constant expressions.

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You can check out the resources section for full list of those.

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But let's look at a few examples now that used the most commonly used rules.

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Typically you would see either Plim Dolittle's or string locos as constant expressions like in the case

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of my doc.

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Here is a simple example of a constant variable the constant expression is simply an intersection.

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In this case we have a string literal as a constant expression.

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This is also a constant expression as a value will be known at compile time itself.

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This is also a valid constraint expression as a final concatenated string is known at compile time itself

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.

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Finally here in the second declaration statement the variable x would be a Garlick constant variable

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as a variable z itself is a constant variable and hence its value is known at compile time and so the

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compiler replaces the variable z with the value for you.

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Now here is the same example we just saw.

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But here Z is not a constant variable as there is no final modifier in its declaration and so X is also

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not a constant variable.

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Here x is not a constant variable as that get to all matter will only be invoked at runtime.

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Here you are declaring a final variable x but it will not be a constant variable as initialization is

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not being done in the declaration statement itself initialization is being done in the constructor and

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the constructor of code is run only at runtime when an object is created.

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Not that objects are created on the Ekron bank.

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Here is a similar example here.

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Variable x is bootstrap big and fine but is not a constant variable as initialization is being done

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in a static initializer block or not in the declaration statement.

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Not that the static initializer block will be run only at runtime when this class has access for the

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very first time at runtime.

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Then this class is access for the very first time.

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Let's say by creating an instance of it or by invoking one off its static matter then JVM just loads

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the class into memory and then it executes this tactic initialize that block.

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At which time the variable is initialized we will deal with this class loading process in JVM in Genesis

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chapter that's the end of our discussion on final variables or not let's look at a quick demo of constant

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variables before turning them on.

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I just want to make a few closing comments.

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Typically you will see final variables as constant variables.

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That is it may not be that common to encounter final variables that object references more of what you

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will see them as constants.

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Tactic redeemers there is constant variables but that static modifier like in the case of mad dog bite

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in general if the variables are valuable not change you can liberally use the final modifier.

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Some programmers tend to use final modifier a lot with local variables like method parameters.

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It is fine but some programmers also feel that it is too verbose and clutters the code.

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Although there can be benefit of some minor compiler optimizations like we discussed earlier so it can

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be your personal choice.

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One suggestion is you may want to consider using Final bit local variables only if it is some special

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kind of construct and it would be worthwhile to highlight it that way.

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You can also check out the resources section for some really good pointers on final variables.

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No need to look at them.

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OK in this demo we are going to use the Java compiler a few times.

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So in the interest of time I'm going to show up on my Eclipse ID as it will save us some time due to

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the number of completions involved.

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So eclipse will help us save some time there.

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So for this demo I'm just going to use the same switch example that we have used the example that we

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have seen in our switch statement.

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OK.

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And the reason I'm doing that is because for if you recall for the switch statement the case label here

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has to be a constant expression and a constant expression can be an integer or a string return or it

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needs to be a constant variable so that just within the context of the switch statement.

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Ok so since it can since it can be a constant variable here and that's what we are testing in this demo

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.

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So we are just picking this example here.

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OK so let's just.

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So this is a switch example if you recall.

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This is the month variable which is initialized with 308 or is byte here and it gets matched to one

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of these labels.

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Unprinted that property value.

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OK so let's just use this exact same example that we have seen and

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our switch DeMaio and we defined a variable called to and it's initialized to 2 and it gives a compiler

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error because it's not a constant expression.

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This gets evaluated only at runtime.

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Again you may recall lot so this needs to be a constant variable and conduct.

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If you recall now it's a constant variable because it is final and importantly it's also initialized

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here in the declaration statement itself.

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Now it's a constant variable.

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Now let's just move this outside off the switch statement of the of the matter.

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So let's just put it here.

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No this will not work.

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And that's because this is an instance where it will know what the method is static and if you recon

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from static method it cannot access instance variables because static methods do not have anything to

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do with state.

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So simple just make it static here.

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Now we are good.

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OK now we are good to compile time constant.

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OK now let's remove that and let's initialize it here.

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Dieu equal do.

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Actually it needs to be a static started block and it's a Mundt do the quiz do.

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Once again this is not going to work because it's not a compile time constant.

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It's not a constant variable and if the reason for that as we discussed the initialization is being

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done in the static initializer block or not in the declaration statement.

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OK and this block will be done only at runtime when this class is loaded into entombment Evangelium

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loaded disgust into memory at that instance.

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Does this initialiser block will be run OK.

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And that would happen if if we make an instance if an instance of this BASIX democracy is made or if

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one of these which one of these static methods are in will only at that point of time the class will

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be loaded into the memory and this static block will be executed.

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OK so there are certain rules when a class has access for the first time and that we will see in the

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JVM internals chapter.

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So let's not worry about that.

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Also here let me just go back and just reiterate here.

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So this was working but if you do this Lun do equal to.

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So if you really initializing this way then once again it's going to be it's going to give us a compilation

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error because it's not the constant variable as it is not initialized in the same line as the declaration

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.

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OK so that's about it.

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So that's about constant variables and that's it.

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Thank you.

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I'm happy coding