1 00:00:00,210 --> 00:00:04,410 For example Mefford one. 2 00:00:04,680 --> 00:00:05,240 OK. 3 00:00:05,430 --> 00:00:08,860 And then I need to put in a semi-colon at the end of my statement. 4 00:00:08,930 --> 00:00:14,210 OK so now I want to actually call the Smurfette from the main effect of this main class. 5 00:00:14,220 --> 00:00:14,640 OK. 6 00:00:14,670 --> 00:00:21,240 So now let me actually comment out these lines of code here because I don't want to execute these lines 7 00:00:21,240 --> 00:00:21,900 of code. 8 00:00:22,070 --> 00:00:22,780 OK. 9 00:00:23,100 --> 00:00:26,710 And then I want to actually call the Smurfette from the main method. 10 00:00:26,940 --> 00:00:31,730 So I just need to refer to the name of mine if it Mefford one. 11 00:00:32,240 --> 00:00:33,200 OK. 12 00:00:33,660 --> 00:00:37,810 And then I need to put in a pair of round brackets after my method name. 13 00:00:38,250 --> 00:00:41,280 So as you can see here it's now showing us an error. 14 00:00:41,310 --> 00:00:47,730 So let's actually hover over the error area and see what's the error cannot make a static reference 15 00:00:48,480 --> 00:00:52,620 to the non-static method one from that type main. 16 00:00:52,830 --> 00:00:56,160 So as you can see here we cannot actually fare through this method. 17 00:00:56,160 --> 00:00:56,580 Why. 18 00:00:56,580 --> 00:00:59,040 Because this it is not static. 19 00:00:59,250 --> 00:01:04,710 Because we are calling this method from the main method of this class. 20 00:01:04,800 --> 00:01:05,360 OK. 21 00:01:05,490 --> 00:01:10,350 So the pointer to this method is our main class. 22 00:01:10,500 --> 00:01:18,860 So in other words if we actually put the static keyword here now the error is gone. 23 00:01:18,900 --> 00:01:23,110 OK now we can actually call this Smurfette from the main method. 24 00:01:23,160 --> 00:01:23,590 OK. 25 00:01:23,610 --> 00:01:30,360 So as you can see here in order to column A fit inside our main method inside our main class we need 26 00:01:30,360 --> 00:01:37,380 to make that specific method a static method or or in other words a class method so that we can actually 27 00:01:37,380 --> 00:01:40,060 referred to that method inside. 28 00:01:40,140 --> 00:01:41,480 Our main method. 29 00:01:41,490 --> 00:01:44,080 Ok this main method is a static method. 30 00:01:44,100 --> 00:01:44,730 OK. 31 00:01:44,880 --> 00:01:48,720 This means that this method is a class method. 32 00:01:48,960 --> 00:01:55,970 So we must actually make this method a class my Fed in order to call this method from this main method. 33 00:01:55,980 --> 00:01:56,720 OK. 34 00:01:57,180 --> 00:01:58,940 So this is very important. 35 00:01:59,220 --> 00:02:07,670 And another important point that I want to touch about is about this system that out that princeling. 36 00:02:07,970 --> 00:02:08,450 OK. 37 00:02:08,550 --> 00:02:14,460 I actually told you that this is the job was very easy in order to output some values to the console. 38 00:02:14,640 --> 00:02:22,080 But now that you know more about classes objects and methods now you can understand what does this statement 39 00:02:22,080 --> 00:02:22,930 mean. 40 00:02:22,950 --> 00:02:25,950 So this system here is a class. 41 00:02:25,950 --> 00:02:26,470 OK. 42 00:02:26,640 --> 00:02:34,380 So now if we actually hover my mouse pointer over this vote here as you can see it says the system class 43 00:02:34,500 --> 00:02:38,260 contains several useful class fields and methods. 44 00:02:38,370 --> 00:02:39,050 OK. 45 00:02:39,420 --> 00:02:41,360 And it cannot be instantiated. 46 00:02:41,370 --> 00:02:44,320 So now we know this system is a class. 47 00:02:44,370 --> 00:02:45,080 OK. 48 00:02:45,420 --> 00:02:54,340 And as you know already a dot operator here as you can see the dot operator can only be used to call 49 00:02:54,340 --> 00:02:56,420 the methods and variables. 50 00:02:56,550 --> 00:03:01,390 So we know that out must be either a method or a variable. 51 00:03:01,440 --> 00:03:06,050 So this out is either a method or a variable. 52 00:03:06,150 --> 00:03:06,860 OK. 53 00:03:07,020 --> 00:03:14,050 Because we used this dot operator here we just referred to the name of our class system dot. 54 00:03:14,220 --> 00:03:18,480 So this out must be our method or our variable. 55 00:03:18,790 --> 00:03:28,650 Ok so how do we actually identify whether this out of is a variable or if it does so out is not a method 56 00:03:28,770 --> 00:03:35,490 because of the fact that there are no Prentice's after our word here after this. 57 00:03:35,490 --> 00:03:37,580 Out here as you can see. 58 00:03:37,650 --> 00:03:43,430 Remember that whenever you call him F-ed you need to put a parenthesis after your name. 59 00:03:43,530 --> 00:03:47,100 So there is no parenthesis after our vote here after this. 60 00:03:47,090 --> 00:03:52,520 Out so this out here is not MF it so it must be of valuable. 61 00:03:52,740 --> 00:03:56,240 OK so we know that out is valuable. 62 00:03:56,280 --> 00:04:01,350 So we must now ask ourselves what kind of variable is it. 63 00:04:01,350 --> 00:04:02,830 There are two possibilities. 64 00:04:03,000 --> 00:04:11,910 It could be it could be a static or an instance variable because out is being called a system class 65 00:04:12,210 --> 00:04:17,880 name itself and not an instance of a class an object for example. 66 00:04:17,880 --> 00:04:21,810 Then we know that out must be a static variable. 67 00:04:21,960 --> 00:04:29,400 Ok so since only static variables can be called with just the class name itself. 68 00:04:29,490 --> 00:04:33,630 So this out here is our static variable. 69 00:04:33,710 --> 00:04:41,440 Ok so now we know that out is a static variable belonging to the system class. 70 00:04:41,520 --> 00:04:42,110 OK. 71 00:04:42,190 --> 00:04:47,600 Now as you can see here we've got this prince Len method here because there are Prentice's after this 72 00:04:47,950 --> 00:04:49,230 printed in here. 73 00:04:49,350 --> 00:04:51,090 This print plant is a method. 74 00:04:51,310 --> 00:04:55,950 Ok this out is a static variable belonging to the class system. 75 00:04:56,070 --> 00:05:02,280 But now we can see that out must be an instance of a class. 76 00:05:02,340 --> 00:05:02,950 Why. 77 00:05:02,970 --> 00:05:06,020 Because it is invoking the Meffert princeling. 78 00:05:06,200 --> 00:05:06,720 OK. 79 00:05:06,900 --> 00:05:11,450 So this out here must be and is an instance of a class. 80 00:05:11,490 --> 00:05:18,420 So now as you can see if I hover my mouse pointer over and this up and vote here out it says print stream 81 00:05:18,660 --> 00:05:21,130 Java that land that system that out. 82 00:05:21,180 --> 00:05:21,780 OK. 83 00:05:22,020 --> 00:05:27,070 So it this out here is up is an instance of the print stream class. 84 00:05:27,230 --> 00:05:28,030 OK. 85 00:05:28,500 --> 00:05:31,250 That is inside the job without the large package. 86 00:05:31,650 --> 00:05:38,280 So as you can see here it says the standard output stream this stream is already open and ready to accept 87 00:05:38,340 --> 00:05:39,570 output data. 88 00:05:39,750 --> 00:05:40,380 OK. 89 00:05:40,380 --> 00:05:48,210 Typically this stream corresponds to display out food or another output destination specified by the 90 00:05:48,210 --> 00:05:50,380 host environment or user. 91 00:05:50,700 --> 00:05:58,020 OK for a simple standalone job applications a typical way to write a line of output data is system that's 92 00:05:58,050 --> 00:06:01,880 out of insulin and then inside the prentices we put our data. 93 00:06:02,220 --> 00:06:07,350 OK so this out here is an instance of the print stream class. 94 00:06:07,350 --> 00:06:08,000 Why. 95 00:06:08,010 --> 00:06:11,650 Because we called the Smurfette on this out here. 96 00:06:11,840 --> 00:06:12,220 OK. 97 00:06:12,240 --> 00:06:16,730 We can only call if it's on our objects or our classes sort this out. 98 00:06:16,730 --> 00:06:24,150 Here is is an instance of the Princeton class and inside the Princeton class we have an instance method 99 00:06:24,870 --> 00:06:26,990 that we call on this out here. 100 00:06:27,060 --> 00:06:28,010 OK. 101 00:06:28,650 --> 00:06:31,840 And that's how we can actually output some data to the console. 102 00:06:31,950 --> 00:06:35,670 So I think that's enough for this tutorial. 103 00:06:35,670 --> 00:06:39,520 If you have any questions please post the discussion in the course. 104 00:06:39,520 --> 00:06:44,160 And thanks very much for watching and I'll see you in the next tutorial.