1 00:00:00,390 --> 00:00:07,170 Hire everyone in this tutorial I'm going to talk about class variables and class methods. 2 00:00:07,200 --> 00:00:07,860 OK. 3 00:00:07,920 --> 00:00:11,550 So first of all we need to create our Java project. 4 00:00:11,550 --> 00:00:18,660 So in order to create a Java project we need to click on File Neo and then click on Java project. 5 00:00:18,690 --> 00:00:27,710 So for the project name just type in here class variables and class methods. 6 00:00:28,200 --> 00:00:28,890 OK. 7 00:00:29,370 --> 00:00:30,600 And click on finish. 8 00:00:30,750 --> 00:00:34,000 So as you can see here our class is now created. 9 00:00:34,200 --> 00:00:39,990 And then if we need our main class for our project in order to actually execute our Java code. 10 00:00:40,020 --> 00:00:40,680 OK. 11 00:00:40,890 --> 00:00:48,240 So just click on this as our See folder and then click on File New and then click on class. 12 00:00:48,630 --> 00:00:51,780 So for the class name just type in here Main. 13 00:00:52,590 --> 00:00:55,720 And for the package we need a reverse domain here. 14 00:00:55,860 --> 00:01:03,950 So just typing here com that your name dot product name class variables 15 00:01:06,410 --> 00:01:10,720 and class methods. 16 00:01:11,250 --> 00:01:11,760 OK. 17 00:01:11,780 --> 00:01:14,690 And then for the modifiers to the public. 18 00:01:14,920 --> 00:01:15,550 OK. 19 00:01:15,560 --> 00:01:19,200 The access modifier of our class is public. 20 00:01:19,910 --> 00:01:25,040 And here make sure that you check these checkbox here public static void main method. 21 00:01:25,040 --> 00:01:25,540 OK. 22 00:01:25,700 --> 00:01:27,310 And then click on finish. 23 00:01:27,860 --> 00:01:31,010 So as you can see here our main class is now created. 24 00:01:31,190 --> 00:01:33,820 So now let me actually delete this comment here. 25 00:01:34,030 --> 00:01:34,590 OK. 26 00:01:34,730 --> 00:01:37,210 Now I want to create bad objects. 27 00:01:37,250 --> 00:01:37,970 OK. 28 00:01:37,970 --> 00:01:41,560 So first of all you need a class called the bird. 29 00:01:41,750 --> 00:01:48,980 So in order to create a class just click on this package here and then click on File New and then click 30 00:01:48,980 --> 00:01:50,130 on a class. 31 00:01:50,270 --> 00:01:52,320 So for the class name just type in here. 32 00:01:53,860 --> 00:01:54,640 OK. 33 00:01:54,950 --> 00:01:57,370 And for the modifier this is public. 34 00:01:57,560 --> 00:02:05,260 And then click on finish so as you can see here our class called Baird is now created. 35 00:02:05,280 --> 00:02:12,720 So now inside of this class I want to put some instructions in order to show me how to create birth 36 00:02:12,720 --> 00:02:13,840 objects. 37 00:02:13,860 --> 00:02:20,910 So first of all I want to create an instance variable for my birth objects so the data type of my instance 38 00:02:20,910 --> 00:02:26,730 variable is it and the name of my instance variable is speed. 39 00:02:27,390 --> 00:02:29,620 And I want to assign a value to my body. 40 00:02:29,640 --> 00:02:31,600 For example 100 than 80. 41 00:02:31,940 --> 00:02:32,680 OK. 42 00:02:33,270 --> 00:02:40,950 And remember that I told you in the previous tutorial that you should always use this private access 43 00:02:40,950 --> 00:02:48,690 modifier for your instance variables in order not to allow any other classes other than disparate class 44 00:02:48,930 --> 00:02:51,900 to access this spit instance variable directory. 45 00:02:51,900 --> 00:02:56,900 OK so now I want to create a getter my friend and I set her my faith for my speed. 46 00:02:56,900 --> 00:02:58,270 Instance variable. 47 00:02:58,590 --> 00:03:03,550 So in order to create or get her in my head I just need to type in here public. 48 00:03:04,000 --> 00:03:04,550 OK. 49 00:03:04,680 --> 00:03:08,480 The access modifier of my get her method is public. 50 00:03:08,490 --> 00:03:09,230 OK. 51 00:03:09,540 --> 00:03:16,850 And the return type of mine if it is in it and the name of my method is get speed. 52 00:03:17,850 --> 00:03:21,970 And then I need to put in a pair of round brackets after my method name. 53 00:03:22,170 --> 00:03:26,460 And then I need to open and close my method by using these curly braces. 54 00:03:26,460 --> 00:03:26,850 OK. 55 00:03:26,850 --> 00:03:33,060 So inside of this nymphet I just need to return the value of my speed instance value of it. 56 00:03:33,090 --> 00:03:36,260 So here I just typed in return speed. 57 00:03:36,310 --> 00:03:37,030 OK. 58 00:03:37,650 --> 00:03:43,940 So now I want to actually create or set her my fed for my speed instance variable. 59 00:03:43,950 --> 00:03:53,280 So again the access modifier of my method is public and the return type of my Meffert is void and the 60 00:03:53,280 --> 00:03:56,690 name of my method is set speed. 61 00:03:57,060 --> 00:04:03,600 And then I need to put in a pair of round brackets after my Meffert name and this time I want to specify 62 00:04:03,870 --> 00:04:06,750 that my method is going to accept an argument. 63 00:04:06,990 --> 00:04:12,620 So the data type of my argument is int and the name of my argument is value. 64 00:04:13,020 --> 00:04:18,110 And then I need to open and close my method by using these curly braces. 65 00:04:18,180 --> 00:04:25,750 So here I want to actually assign the value of my argument to my speed instance variable. 66 00:04:25,890 --> 00:04:29,940 So first I need to refer to the name of my speed instance variable. 67 00:04:30,300 --> 00:04:35,830 And then I put an assignment operator here and then I refer to the name of my argument. 68 00:04:36,120 --> 00:04:45,930 OK so now I might get her method and my certain method for this instance variable is created. 69 00:04:46,050 --> 00:04:50,840 So now I want to actually create a behavior for my birth objects. 70 00:04:50,850 --> 00:04:55,060 So again the access modifier of my method is public. 71 00:04:55,140 --> 00:05:00,780 So for the behaviors of your objects always use the public access modifier. 72 00:05:00,780 --> 00:05:01,540 OK. 73 00:05:01,650 --> 00:05:07,560 Or you can actually use the package access modifier if you want to only allow the classes inside of 74 00:05:07,560 --> 00:05:10,200 this package to use that behavior. 75 00:05:10,200 --> 00:05:10,610 OK. 76 00:05:10,620 --> 00:05:15,720 So in order to actually use the package access modifier you don't need to write any key word here. 77 00:05:15,720 --> 00:05:16,310 OK. 78 00:05:16,500 --> 00:05:22,930 The package access modifier is the default access modifier for all of your variables and methods. 79 00:05:23,010 --> 00:05:25,470 So the return type of My method is void. 80 00:05:25,900 --> 00:05:28,780 And for example my bird can fly. 81 00:05:28,840 --> 00:05:35,740 OK so the name of my method is fly and then I need to put in a pair of round brackets after my name 82 00:05:36,060 --> 00:05:42,420 and then I need to open and close my fit by using these curly braces and inside of this if I can't put 83 00:05:42,420 --> 00:05:43,920 my statements. 84 00:05:43,920 --> 00:05:50,710 So here I just need to type in system that's out that insulin. 85 00:05:50,890 --> 00:05:56,620 And then inside the prentices I just put it into double quotes here and then inside of these double 86 00:05:56,620 --> 00:05:59,110 quotes I can just type in fly. 87 00:05:59,230 --> 00:06:03,150 And then I need to put in a semi-colon at the end of my statement. 88 00:06:03,190 --> 00:06:06,590 So as you can see here our blueprint is now ready. 89 00:06:06,880 --> 00:06:11,160 So now we want to create weird objects from disparate class. 90 00:06:11,170 --> 00:06:11,700 OK. 91 00:06:11,740 --> 00:06:17,320 So inside of this main class here I just need to double click on this means that we have here in order 92 00:06:17,320 --> 00:06:20,230 to make this a little earlier or much wider. 93 00:06:20,260 --> 00:06:24,310 So now we want to create objects from this birth class. 94 00:06:24,310 --> 00:06:32,870 So first of all I need to refer to the name of my class bird and the name of my object is my beard and 95 00:06:32,860 --> 00:06:35,200 that I put an assignment operator here. 96 00:06:35,470 --> 00:06:38,000 And then I use this key word here new. 97 00:06:38,560 --> 00:06:43,580 And then again you refer to the name of my class and then I put in a pair of round brackets. 98 00:06:43,720 --> 00:06:44,800 After my class name. 99 00:06:44,880 --> 00:06:50,210 OK so now I can actually access the characteristics or behaviors of my birth object. 100 00:06:50,230 --> 00:06:50,750 OK. 101 00:06:50,950 --> 00:06:57,030 So for example I want to access the value of the speed instance variable and then outputs that value 102 00:06:57,040 --> 00:06:57,840 to the console. 103 00:06:58,000 --> 00:07:05,650 So I just to type in here system that out that insulin and it inside of the prentices. 104 00:07:05,650 --> 00:07:12,650 First I need to refer to the name of my object my bird that gets speed OK. 105 00:07:12,790 --> 00:07:16,260 And then I need to put in a semicolon at the end of my statement. 106 00:07:16,270 --> 00:07:21,760 So now if I run my project as you can see this is the value of the speed instance variable. 107 00:07:21,760 --> 00:07:22,290 OK. 108 00:07:22,450 --> 00:07:29,690 Or I can actually tell my birth object to fly my birth dot fly. 109 00:07:30,030 --> 00:07:30,580 OK. 110 00:07:30,760 --> 00:07:35,820 And now if I run my project as you can see this value is outputted to the console. 111 00:07:35,830 --> 00:07:44,190 OK so now I going to actually talk about class variables and class methods. 112 00:07:44,230 --> 00:07:49,930 Class variables are variables defined and stored in the class itself. 113 00:07:49,930 --> 00:07:57,380 Their values apply to the class and all its instances with instance variables. 114 00:07:57,400 --> 00:08:05,500 Each new instance of the class gets a new copy of the instance variables that the class defines each 115 00:08:05,500 --> 00:08:13,570 instance then can change the values of those instance variables without affecting any other instances. 116 00:08:13,570 --> 00:08:17,600 OK I actually showed you some of those examples in the previous tutorials. 117 00:08:17,650 --> 00:08:26,470 I told you that every object actually gets a new copy of the instance valuable that we define in that 118 00:08:26,470 --> 00:08:27,360 specific class. 119 00:08:27,370 --> 00:08:27,900 OK. 120 00:08:28,090 --> 00:08:36,130 So for example if I change the value of the speed instance valuable for this my birth object we are 121 00:08:36,130 --> 00:08:40,500 actually changing a copy of that instance variable. 122 00:08:40,510 --> 00:08:41,000 OK. 123 00:08:41,050 --> 00:08:47,050 And if I create another object from this class the value of that instance variable is going to be unchanged. 124 00:08:47,080 --> 00:08:47,730 OK. 125 00:08:47,830 --> 00:08:52,690 Because we are only creating a copy for our object. 126 00:08:52,690 --> 00:08:55,510 For every object that we create from this class. 127 00:08:55,570 --> 00:09:04,000 Ok this is for instance variables but with class variables is only one copy of that variable exists. 128 00:09:04,000 --> 00:09:11,920 When the class is loaded changing the value of that variable changes it for all instances of that class 129 00:09:11,930 --> 00:09:18,180 redefined class variables by including the static keyword before the value itself. 130 00:09:18,290 --> 00:09:23,590 OK so now let me actually show you some real examples in order to make this concept more meaningful 131 00:09:23,830 --> 00:09:24,730 for you. 132 00:09:24,730 --> 00:09:27,740 So first let me actually comment out these lines of code here. 133 00:09:27,850 --> 00:09:28,560 OK. 134 00:09:28,870 --> 00:09:35,320 And now inside the bird's class here and now inside the parent class here. 135 00:09:35,350 --> 00:09:39,830 Firstly actually change this private access modifier to public. 136 00:09:40,380 --> 00:09:40,950 OK. 137 00:09:41,170 --> 00:09:47,710 And then we need to put this tatic vote here after our access modifier in order to make this instance 138 00:09:47,710 --> 00:09:49,400 valuable a class variable. 139 00:09:49,420 --> 00:09:50,010 OK. 140 00:09:50,010 --> 00:09:50,530 Static.