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We can use the equals method to check if two objects are equal.

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In this lesson, you're going to add an equals method to a class.

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You can access this lesson by following this path and the resources and open the equals folder.

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The default equals method compares the references of two objects.

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Create one object of the car class.

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Toyota blew.

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And then set a variable, same car equal to the car.

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Now, both car and same car share a reference to the same object.

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Check if CA equals same car.

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And it returns true because both variables store the same reference.

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When you set same car equal to car, it copies the reference, and since both share the same reference,

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then the equals method determines that they are indeed equal.

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But that's the thing, too, variables should not share a reference to the same object.

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Otherwise, you're going to risk falling into the reference trap.

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So we're going to see that same car equal to a new copy of the first car object.

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The two objects are exact copies of each other, but because they don't share the same reference than

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the equals method determines that they're not equal.

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We can customize the equals method for a specific class.

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We can customize it to compare the fields of two objects, we're going to customize the equals method

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for objects of the car class.

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And as you can see, the equals method returns a boolean and it receives an object, what's the type

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of that object?

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We don't know.

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It can be any object.

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OK, car calls the equals method and pass the same cars in argument.

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This points to the current object calling the equals method.

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OBJ points to the object that was passed in.

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And nothing happens inside the function, it just returns true.

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That's not very useful.

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Here is how to make the perfect equals method.

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First, you're going to return false if the object that was passed then is null.

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Then you're going to return false if the object is not an instance of the specified type.

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If it happens to be an instance of the specified type, then you're going to typecast it.

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Then you're going to compare every field from both objects and return the results.

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In the equals method check if the object was passed in, is No.

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And if that's the case, return false, there's no way the object that's calling the equals method is

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going to equal null, otherwise it would have thrown a null pointer exception.

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All right, now return false if the object that was passed in is not an instance of car and we can do

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that using the instance of keyword, so we'll check if the object is an instance of car and reverse

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it to say if the object is not of type car, then we'll return false.

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Although if the object was passed in is an instance of car, then we are going to make it to this line

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so we can typecast object to a car type.

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And now we can access Hadfield's.

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So what I'm going to do is compare every field from the current object calling the equals method, this

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with every field from the car object that was passed in.

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OK, time to test it inside, men, I'm going to pass a nail into the equals method.

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This points to the current object and the argument we passed in is no to the equals method is going

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to return false because there's no way a null is going to equal the object that's calling this method.

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All right, now I'm going to create a scanner object.

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And pass it into the equals method.

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This points to the car object calling the method the object we passed in with scanner.

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The object is not no to passes this test.

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But the object is not an instance of car, so there's no way it's going to equal the car object that's

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calling this method equals returns false and determines that these objects are not equal.

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We'll try that out.

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The object is not know, so it passes this test.

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The object is of type car, so it passes that test.

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The fields from both objects are equal to each other, so this condition returns true and the equals

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method tells us that they are equal.

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OK, now we're going to compare two car objects that don't equal each other, so I'll change this to

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Honda.

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All right, this object is not known.

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So it passes this test.

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The object is of type car, so it passes this test.

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But the fields are equal to each other.

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So this condition returns false and the equals method determines that these objects are not equal,

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and you know what?

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If you ask me, it works perfectly.

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To recap, you customize the equals method for the car class.

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The default equals method compares the references of two objects, which isn't very useful.

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We customize the equals method to compare the fields from two car objects.