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Inheritance in Java

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Object Methods

3:29 with Ben Deitch

In this video we'll explore the methods of the Object class.

Correction

The code example at 1:35 in the video shows: mary.hashCode() != frank.hashCode(); // Returns false

Since both objects return a different hashcode, they are not equal to each other, so the comparison should return true. It's true that Mary's hashcode is not equal to (!=) Frank's hashcode.

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    Hopefully by this point, 0:00
    it's starting to click that everything in Java is an object. 0:01
    But what sort of functionality do we get from the object class? 0:04
    Up in the main method, let's clear out what we've got and 0:08
    start fresh with a new dog variable. 0:11
    Dog, name it dog = new Dog. 0:14
    Then let's add a line and type dog., to look at our options. 0:18
    Here, everything except for the sound field, and 0:22
    the makeSound method comes from the object class. 0:27
    Now, most of these you don't need to worry about, but 0:32
    there's a few you really should know like equals, hashCode, toString, and getClass. 0:36
    Let's start with the getClass method. 0:42
    When you call the getClass method on an object, 0:45
    it returns a class object that contains information about the class itself. 0:48
    Like the class name and what package it's in. 0:54
    Moving to the toString method, when you call toString on an object, 0:57
    it returns a string with information about the object. 1:02
    So if we wanted to print out what was in an object, 1:06
    we would use the toString method. 1:09
    Hashcode is a little different. 1:11
    When you call the hashcode method on an object, 1:13
    you get back an integer representing that object. 1:16
    However, the important thing is that the hashcode method will 1:19
    return a different integer for every object. 1:23
    So one way to check if an object is equal to another would be to check 1:26
    their hashcodes. 1:30
    If they've got the same hash code, they're the same object. 1:32
    The other way to check if two objects are equal would be to use the equals method. 1:35
    Which returns a boolean indicating if the two objects are equal. 1:40
    Awesome! 1:44
    Back in the code, lets get some practice with these methods. 1:45
    First let's print out the result of calling toString on our Dog object. 1:49
    Let's delete this dog., and then type sout, 1:54
    and print out dog.toString. 1:59
    And then, let's run the app, and there we go. 2:03
    We've got some information about our object. 2:08
    Looks like we've got the class name followed by an at, and 2:11
    then some letters and numbers. 2:16
    Let's take a deeper look at the toString method to figure out what's going on here. 2:19
    In IntelliJ, whenever you want to take a deeper look at something, 2:24
    you just put your cursor on it and use Cmd or Ctrl+B to jump to its declaration. 2:29
    Let's click on toString and then hit Cmd or Ctrl+V, and I'll hide the run pane. 2:35
    Here we have the toString method from the Object class. 2:42
    And if we look inside, we can see that it's returning get class 2:46
    dot get name to get the class name, followed by an at sign. 2:51
    And then it looks like that last bit was just the hash code represented as 2:56
    a hex string. 3:01
    Also, sometimes when you use Cmd or Ctrl+B, 3:02
    if you're lucky, you'll get some documentation like we did here. 3:05
    We already know most of this just from reading the code. 3:12
    But let's take a look at this bit. 3:16
    It is recommended that all subclasses override this method. 3:18
    Override? 3:24
    What does that mean? 3:25
    We'll find out in the next video. 3:27

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