1 00:00:02,240 --> 00:00:04,123 So now that we learned 2 00:00:04,123 --> 00:00:05,580 about the Law of Demeter, we should dive 3 00:00:05,580 --> 00:00:09,700 into a couple of other often cited principles, 4 00:00:09,700 --> 00:00:13,380 which you should be aware of when working with classes 5 00:00:13,380 --> 00:00:18,380 and especially when writing code in an object oriented way. 6 00:00:18,970 --> 00:00:22,530 And here, amongst the most popular principles, 7 00:00:22,530 --> 00:00:26,550 we would have the so-called SOLID principles. 8 00:00:26,550 --> 00:00:29,980 We should write classes in a SOLID way, 9 00:00:29,980 --> 00:00:33,370 and SOLID is an acronym which stands 10 00:00:33,370 --> 00:00:37,240 for five different principles which you should apply 11 00:00:37,240 --> 00:00:40,300 to your classes, so which you should respect 12 00:00:40,300 --> 00:00:43,900 when writing code, to end up with clauses 13 00:00:43,900 --> 00:00:46,990 which are considered to be well-written, 14 00:00:46,990 --> 00:00:50,100 extensible and maintainable. 15 00:00:50,100 --> 00:00:53,900 Now here's what these different characters stand for. 16 00:00:53,900 --> 00:00:58,900 The S principle is the single responsibility principle, 17 00:00:59,240 --> 00:01:02,330 and we're going to have a closer look at these principles 18 00:01:02,330 --> 00:01:04,113 over the next minutes, of course. 19 00:01:05,210 --> 00:01:08,840 O stands for open-closed principle, 20 00:01:08,840 --> 00:01:12,260 L for Liskov substitution principle, 21 00:01:12,260 --> 00:01:16,000 I for interface segregation principle, 22 00:01:16,000 --> 00:01:20,520 and D for dependency inversion principle. 23 00:01:20,520 --> 00:01:23,180 These are the SOLID principles 24 00:01:23,180 --> 00:01:24,960 which you typically should follow 25 00:01:24,960 --> 00:01:28,360 when writing object oriented code. 26 00:01:28,360 --> 00:01:32,240 Now, it's especially the S and O principles 27 00:01:32,240 --> 00:01:35,450 which also matter to us when writing clean code 28 00:01:35,450 --> 00:01:37,570 because, as mentioned multiple times, 29 00:01:37,570 --> 00:01:40,370 whilst all patterns and principles, 30 00:01:40,370 --> 00:01:43,690 of course, tend to make our code cleaner, 31 00:01:43,690 --> 00:01:46,190 we especially have two principles here 32 00:01:46,190 --> 00:01:51,190 which have a very clear impact on the cleanness of our code. 33 00:01:51,470 --> 00:01:53,710 So therefore, let's take a closer look 34 00:01:53,710 --> 00:01:58,200 at the single responsibility and the open-closed principle, 35 00:01:58,200 --> 00:02:00,500 but, of course, let's also briefly look 36 00:02:00,500 --> 00:02:03,433 at the other principles over the next minutes.