1 00:00:01,140 --> 00:00:07,620 Not look at the data structure called it is software it gets lot of its power through data structures 2 00:00:07,620 --> 00:00:14,080 that it uses and the data structure is an organized collection of related data. 3 00:00:14,100 --> 00:00:19,980 For example if you want to print all the CT status that a student has registered for then watch this 4 00:00:19,980 --> 00:00:24,960 course titles in some kind of a data structure before printing them later. 5 00:00:24,970 --> 00:00:28,550 You look at several of these powerful built in data structures. 6 00:00:29,070 --> 00:00:34,290 However there is one very basic data structure that is built into every programming language and it's 7 00:00:34,290 --> 00:00:35,690 an art. 8 00:00:35,780 --> 00:00:41,160 In fact it is so basic that even some of the data structures that we study later are built on top of 9 00:00:41,250 --> 00:00:47,090 arrays pre-knowledge just look at arrays and we will study other data structures later. 10 00:00:48,270 --> 00:00:54,880 And that is basically a container object that holds a fixed number of values of a single type. 11 00:00:54,960 --> 00:00:57,650 Some of the terms in this definition are emphasized in bold. 12 00:00:57,800 --> 00:01:00,100 And let's understand what they mean. 13 00:01:00,300 --> 00:01:05,570 The term object in this definition implies a Java object that is in Java. 14 00:01:05,610 --> 00:01:11,400 An array is basically an object and hence will be stored on the heap like any other object. 15 00:01:11,520 --> 00:01:18,250 Since R is an object the variable referencing it is an object reference next to a fixed number which 16 00:01:18,250 --> 00:01:23,970 means that the number of items they can store is decided at the array creation time itself and cannot 17 00:01:23,970 --> 00:01:30,570 be changed thereafter finally by a single type we mean that the items in an RV should be of a single 18 00:01:30,570 --> 00:01:37,660 data type like N and R double or even some class that is an array can store primitives or object or 19 00:01:37,660 --> 00:01:44,120 Francis but only condition is that they have to be of the same type. 20 00:01:44,140 --> 00:01:48,490 Here is an illustration of an array which contains seven integer values. 21 00:01:48,780 --> 00:01:55,290 Each item in the array is called an element and this axis by its next number an index number is nothing 22 00:01:55,320 --> 00:02:02,620 but the numerical position of the element in the ID and index numbering begins with zero. 23 00:02:03,550 --> 00:02:09,450 Now if this array is named as my array then the fourth element which is a value 5 is accessed in this 24 00:02:09,450 --> 00:02:10,140 way. 25 00:02:10,520 --> 00:02:15,360 That is you will have the Aryanism followed by square brackets with the index number in between the 26 00:02:15,360 --> 00:02:17,020 square brackets. 27 00:02:17,370 --> 00:02:18,140 Multiple axis. 28 00:02:18,140 --> 00:02:24,000 Fourth element the next number will be three as index numbering starts with zero. 29 00:02:25,050 --> 00:02:28,380 No coming to creating an array there are three ways to do it. 30 00:02:28,800 --> 00:02:33,160 Let's look at how we can create our example or a call to my at it. 31 00:02:33,240 --> 00:02:38,520 Let's just look at the case where an arrest or primitives later we will see an example where underresourced 32 00:02:38,610 --> 00:02:43,560 object references and hit is a fast way to do it. 33 00:02:43,560 --> 00:02:49,020 We use the word new knew the number of elements that are it would store is indicated in square brackets 34 00:02:49,020 --> 00:02:50,130 . 35 00:02:50,130 --> 00:02:54,970 This declaration is quite similar to the declaration we saw for creating objects. 36 00:02:55,020 --> 00:02:59,840 The difference is that in this index we how additional square brackets on the left hand side of that 37 00:02:59,840 --> 00:03:02,180 assignment are on the right hand side. 38 00:03:02,200 --> 00:03:09,990 MP balances is replaced by square brackets since the arrays of pipe and each element will by default 39 00:03:09,990 --> 00:03:11,690 be zero that is. 40 00:03:11,700 --> 00:03:17,270 Each element is basically an end variable and is initialized with a default value an inquiry. 41 00:03:17,270 --> 00:03:18,140 But you can get. 42 00:03:18,210 --> 00:03:19,580 Which is zero. 43 00:03:20,100 --> 00:03:25,320 So do the R.H. then if it's an object it's elements here are primitives. 44 00:03:25,320 --> 00:03:32,220 Next step would be to initialize each element all the seven elements are initialized in this way using 45 00:03:32,220 --> 00:03:34,140 their next numbers. 46 00:03:34,140 --> 00:03:41,110 The Szilard element is initialized with the value 9 first element with the value 11 and so on. 47 00:03:41,110 --> 00:03:43,160 Not since an array is an object. 48 00:03:43,290 --> 00:03:48,840 If the other declaration contains only that type under array name then that variable gets the default 49 00:03:48,840 --> 00:03:49,460 value. 50 00:03:49,470 --> 00:03:53,510 Any object reference gets which is null. 51 00:03:53,550 --> 00:03:55,730 Here is the second way to create an array. 52 00:03:55,870 --> 00:04:02,040 Syntax is similar to the first approach but with two differences is Element initialization is done in 53 00:04:02,040 --> 00:04:05,340 the declaration itself and between the two braces. 54 00:04:05,460 --> 00:04:09,280 Second difference is we have empty square brackets on the right hand side. 55 00:04:09,480 --> 00:04:12,210 That is we don't explicitly specify the array size. 56 00:04:12,360 --> 00:04:17,190 I is automatically inferred from the number of elements used to initialize the. 57 00:04:17,430 --> 00:04:23,320 In this case it is 7 specifying that RSS will result in a compile time error. 58 00:04:24,620 --> 00:04:27,380 Finally to create an array has a simpler syntax. 59 00:04:27,840 --> 00:04:30,780 Right answer in quotes only element initialization. 60 00:04:30,920 --> 00:04:36,930 There is no Nuki word order type information with the square brackets. 61 00:04:36,930 --> 00:04:42,720 Finally we saw that in all three array creation examples the declaration began with the element type 62 00:04:42,720 --> 00:04:45,500 followed by empty square brackets. 63 00:04:45,560 --> 00:04:51,170 However it is perfectly legal to also have the empty square brackets after the are in him instead of 64 00:04:51,180 --> 00:04:53,690 the element type like we see here. 65 00:04:54,330 --> 00:04:59,580 Personally I prefer to have it after the element type and that's because on the right side also the 66 00:04:59,580 --> 00:05:02,430 square brackets follow the element type. 67 00:05:02,430 --> 00:05:08,270 So it's just for the sake of consistency but it is entirely up to you. 68 00:05:08,280 --> 00:05:11,010 Often we need to know the length or size of the army. 69 00:05:11,100 --> 00:05:14,110 That is the number of elements or array contents. 70 00:05:14,110 --> 00:05:20,490 And for this we can use the length of the ID that is left is a feat within the array object as an array 71 00:05:20,490 --> 00:05:23,480 is an object as we already discussed. 72 00:05:24,480 --> 00:05:33,040 So for our miring example accessing lanthanum my very variable returns the value 7 we know that aria 73 00:05:33,050 --> 00:05:38,730 has a fixed number of elements and so accessing an element outside of the boundary will result in an 74 00:05:38,850 --> 00:05:41,500 added runtime. 75 00:05:41,760 --> 00:05:47,610 For example my idea has only seven elements and so trying to access elements beyond the seventh element 76 00:05:47,810 --> 00:05:50,670 really do are on parameter in this example. 77 00:05:50,670 --> 00:05:56,370 We are trying to access the eighth element which is stored in next number 7 and it will result in a 78 00:05:56,370 --> 00:05:58,970 runtime error. 79 00:05:59,100 --> 00:06:05,180 So we looked at arrays containing primitives but arrays can also store object references. 80 00:06:05,280 --> 00:06:08,550 And here is an example similar to an array of ends. 81 00:06:08,640 --> 00:06:15,360 We can create an array of object references here and article students is created which can store boost 82 00:06:15,360 --> 00:06:23,760 with an object or Francis as you can see the type of the R is simply changed from end to student. 83 00:06:23,760 --> 00:06:29,880 Since each element is an object reference but default each element gets initialized with no. 84 00:06:31,170 --> 00:06:36,000 Since each element is an object reference we can initialize each element by assigning a new student 85 00:06:36,000 --> 00:06:37,220 object. 86 00:06:37,290 --> 00:06:43,920 So each element no references that student object on so we can also initialize each element state in 87 00:06:43,920 --> 00:06:47,270 this bit using the dot operator. 88 00:06:47,310 --> 00:06:52,620 So basically arrays can store either primitives or object references on be no understand how it can 89 00:06:52,620 --> 00:06:55,080 be done. 90 00:06:55,090 --> 00:07:01,980 Now let's discuss a bit about how arrays are represented within memory Gibeon specification doesn't 91 00:07:01,980 --> 00:07:05,540 say anything about how an object is stored inside memory. 92 00:07:05,920 --> 00:07:06,430 Hello. 93 00:07:06,450 --> 00:07:12,420 It is generally believed that most GBM implementations use a mediately out when it comes to. 94 00:07:12,810 --> 00:07:16,080 That is that our elements are stored contiguously. 95 00:07:16,080 --> 00:07:19,400 In other words they are stored next to each other in the memory. 96 00:07:19,740 --> 00:07:22,140 And this and also fast random access. 97 00:07:22,440 --> 00:07:26,820 There is any element can be accessed in in constant time. 98 00:07:26,820 --> 00:07:33,780 So accessing Tozan element would take the same amount of time as accessing the fifth element the element 99 00:07:33,780 --> 00:07:38,180 access is extremely fast if you want to search for a particular item in the array. 100 00:07:38,250 --> 00:07:44,170 Then that would be linear time as we have to scan the directory starting from the first element. 101 00:07:44,670 --> 00:07:51,000 Later we would look at data structures that are designed specifically for fast searching not just look 102 00:07:51,000 --> 00:07:54,870 at a very simple and quick them off our list. 103 00:07:56,230 --> 00:08:01,110 OK in this demo we're going to fill up this new method called arrays and it's in walk from the main 104 00:08:01,110 --> 00:08:05,370 method and all the previous method invocations have been commented out. 105 00:08:05,880 --> 00:08:07,840 So we'll be just testing fewer things here. 106 00:08:07,860 --> 00:08:12,620 One is we'll create an array using the second approach that we solve for creating arrays. 107 00:08:12,930 --> 00:08:17,990 Then we will use the lenth function lengthy and really does that. 108 00:08:17,990 --> 00:08:21,840 And then we would also look at how we can access the elements right. 109 00:08:21,840 --> 00:08:22,470 We can use it. 110 00:08:22,470 --> 00:08:25,570 We can access the elements using and mixed numbers and we would also apply order. 111 00:08:25,590 --> 00:08:27,480 So it's going to be a really simple demo. 112 00:08:27,810 --> 00:08:34,320 So just go ahead and create the array and we will create the exact same idea that we have seen earlier 113 00:08:34,320 --> 00:08:36,180 . 114 00:08:36,360 --> 00:08:40,450 So let's just call it and followed by Grad rockets. 115 00:08:40,590 --> 00:08:44,850 Let's just call it my theory as we have seen in this light. 116 00:08:45,120 --> 00:08:48,460 It's in you and in the second approach. 117 00:08:48,580 --> 00:08:55,440 We'll have this kind of an operation followed by basis and we are going to initialize the elements right 118 00:08:55,440 --> 00:08:56,500 here in the declaration. 119 00:08:56,550 --> 00:08:59,810 So I have just copied that. 120 00:09:00,150 --> 00:09:08,850 So those are those are the same elements not just put in some of the things system not all or brindled 121 00:09:08,850 --> 00:09:14,960 and to just turn the Leonti just so let's see my re. 122 00:09:15,090 --> 00:09:19,800 Them niggas copy this. 123 00:09:20,010 --> 00:09:25,510 So this is going to print the size of the ID next leps access of all of the elements. 124 00:09:25,530 --> 00:09:28,700 So let me just copy this whole thing. 125 00:09:29,190 --> 00:09:38,240 It's axis the second element which is Axis using the element and next number one. 126 00:09:39,210 --> 00:09:46,680 So let's just go ahead and compile and does this by it's fine. 127 00:09:46,710 --> 00:09:47,390 So there you go. 128 00:09:47,400 --> 00:09:48,650 So we are inside our base. 129 00:09:48,690 --> 00:09:54,110 The ideal to 7 and the first the second element is basically 11. 130 00:09:54,150 --> 00:09:54,690 OK. 131 00:09:54,720 --> 00:10:01,740 This is what it is not it's just trying to access an element which is outside the boundary of I. 132 00:10:02,190 --> 00:10:08,820 So the idea has seven elements so let's just try to access the 8 element which is accessed using the 133 00:10:08,940 --> 00:10:11,490 next number 7. 134 00:10:12,560 --> 00:10:19,400 It's really compiled and this should give a runtime error and that's what we get here. 135 00:10:19,410 --> 00:10:22,950 It's this array index out of bounds exception. 136 00:10:23,100 --> 00:10:24,820 So we are getting a runtime error. 137 00:10:24,910 --> 00:10:29,370 And that's because we are trying to access something outside the boundary of the ID. 138 00:10:29,820 --> 00:10:32,090 OK so those are three simple things here. 139 00:10:32,240 --> 00:10:35,890 And so we now have an understanding of this. 140 00:10:36,120 --> 00:10:42,020 So the main thing that we need to remember about arrays is an arm is basically an object in yellow. 141 00:10:42,180 --> 00:10:45,780 OK I it will have a fixed number of elements. 142 00:10:45,810 --> 00:10:49,740 That's one thing I and all the elements should be of single type. 143 00:10:49,740 --> 00:10:53,640 In this case it is and but it can also be object references. 144 00:10:53,640 --> 00:11:00,660 So later in the project Beeville in the first version rule extensively use arrays undir we will we will 145 00:11:00,660 --> 00:11:04,260 try we'll create lot of ways that store object references. 146 00:11:04,410 --> 00:11:11,130 OK unjaded We will also look at other data structures sophisticated radar structures and that's about 147 00:11:11,130 --> 00:11:11,430 it. 148 00:11:11,430 --> 00:11:18,050 So just go ahead and you can find the updated basics democracy in the resources section and you can 149 00:11:18,060 --> 00:11:22,810 now download and exit this file it's a good program and you can play around with that. 150 00:11:22,950 --> 00:11:23,450 OK then. 151 00:11:23,460 --> 00:11:23,930 Thank you. 152 00:11:23,940 --> 00:11:25,110 And happy coding.