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A constant is a variable that can never change.

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A value that isn't supposed to change shouldn't.

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Constants are variables that can never change.

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In this lesson, you will define a static final constant.

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What is a constant, as I just said twice, a value that can never change?

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Why do we use constants to ensure values that shouldn't change, don't?

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And why are constant static, because they belong to the class, their value doesn't change regardless

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of the object.

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A field is not static because it has different values for each object.

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In other words, each field belongs to a particular object.

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A constant is the same across every object, regardless of the object, every employee works for the

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same company, so a constant belongs to the class.

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So why are constants final, final means you can never update the variable, a constant is a value that

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should never change.

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So the state of the constant needs to be final.

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Inside employed out Java, you'll notice that I'm plainly writing the company name Java Stars, this

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is an important value because it affects our code.

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Imagine I accidentally change it here, but here I leave it.

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This is bad because now everything is inconsistent and I'm vulnerable to getting bugs never play the

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right an important value, you might change it by mistake.

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Instead, use a constant.

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So here, instead of rewriting the same value over and over.

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I'm going to create a static final string.

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Constant company name Java stars.

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This is the naming convention for constants, every letter is uppercase and words are separated by an

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underscore.

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This information is in your cheat sheet.

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But what's important is that now, instead of writing the same value over and over, I can keep referencing

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the constant.

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And if you ask me, this is a lot cleaner and it's a lot safer.

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Should the constant be private, if there's no reason to make it public, then yes.

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The constant is final, so I'm not worried about the color accidentally changing it, the color could

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try, but it's not possible.

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Here, I'll show you.

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Java just won't let them see.

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So we could leave it as public, but there isn't a reason to make it publicly available outside the

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class, so it's good practice.

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And honestly, even if you want to expose the value for whatever reason, it's good practice to just

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give it a go getter that returns a copy of that value.

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You might be wondering why do we need a GETER that returns a copy of the constant value of the constant

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is final.

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There's no point, it's just good practice.

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If you decide not to include a getter and just make the constant public, that's fine, it's honestly

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just a matter of opinion.

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OK, now we're going to open up the movie star solution.

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Looking at the movie class, can you guess what needs to be a constant.

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The String Values DVD and Blu ray, what we did here by rewriting DVD and Blu ray over and over is extremely

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bad practice.

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We were basically playing with fire.

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Can you imagine if I misspelled one of them, I would get so many bugs.

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So what I'm going to do is make a constant for DVD private static Final String.

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Format DVD.

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Is equal to DVD.

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And a constant for Blu ray.

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Format Blu ray is equal to Blu ray.

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Now, I can refer to each constant where I need to.

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All right, let's recap a constant, the static, because it belongs to the class, it does not belong

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to an object, a constant is final because it should never change.

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Use a constant to ensure a value that shouldn't change, doesn't.