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An interface defines method that a class needs to implement.

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If a class implements an interface, it must override all of the methods inside the interface.

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In this lesson, one of your classes is going to implement an interface.

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An interface is a contract, and the contract defines methods that a class needs to implement.

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Use an interface to define behavior that's required from a class, because if a class implements an

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interface, it must override all of the methods inside the interface.

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You can define an interface the way you would define a class public interface, followed by the interface

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name.

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And inside the interface, you can define method signatures, a class that implements this interface

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must override every method inside of its.

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So looking back at the requirements, we see that pense are eligible for 50 percent discounts, but

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shirts are not.

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But what I want to do is force the pants class to implement this behavior.

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So I'll define an interface, create a new file, discounted Java.

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And inside this kind of job, Java make this an interface.

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And we're going to force every class and implement this interface to override a public void method called

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discount.

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And now inside Penstock Java, we can say that the pants class implements the discount interface.

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When a class implements an interface, it's basically signing a contract that it's going to override

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all of the methods inside the interface.

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And here we have to honor the contract to override discount.

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And we're going to offer a 50 percent discount by saying superdog set price.

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Superdog get price divided by two.

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And now the air is gone.

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So back in Maine, we can call Penn student discount.

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Put a breakpoint, launched the debugger.

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And the price of the object went down by 50 percent.

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Now, what's really interesting is that interfaces allow for polymorphism.

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Because pants are discounted so we can declare the object as type discounted.

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Keep this in mind for your next quiz.

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An interface is a contract.

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It defines methods that a class needs to implement.

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When a class implements an interface, it signs the contract, therefore the class must override all

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of the methods inside the interface.