1 00:00:04,900 --> 00:00:06,280 In this video we'll just take a look 2 00:00:06,280 --> 00:00:07,600 at some decision constructs 3 00:00:07,600 --> 00:00:09,850 that you may not necessarily ever use 4 00:00:09,850 --> 00:00:12,160 but that should point out items to look for 5 00:00:12,160 --> 00:00:13,770 on the certification exam. 6 00:00:13,770 --> 00:00:15,465 So let's start by looking at the switch statement 7 00:00:15,465 --> 00:00:16,570 and we're gonna create a new class 8 00:00:16,570 --> 00:00:20,270 in our decisions project 'SwitchStatementOddities.' 9 00:00:20,270 --> 00:00:21,503 I'll paste in some code. 10 00:00:26,200 --> 00:00:27,350 Okay, there's the code. 11 00:00:28,750 --> 00:00:30,200 So terms of this code, 12 00:00:30,200 --> 00:00:33,000 it contains an array of byte assigned values, 13 00:00:33,000 --> 00:00:35,610 a for loop that loops through the array of byte values, 14 00:00:35,610 --> 00:00:38,400 also contains a switch statement with an expression in it, 15 00:00:38,400 --> 00:00:41,030 which simply multiplies the pass value by 10 16 00:00:41,030 --> 00:00:42,530 and the switch statement labels 17 00:00:42,530 --> 00:00:45,440 should now match the value in the switch expression. 18 00:00:45,440 --> 00:00:46,790 So let's actually run this. 19 00:00:49,520 --> 00:00:52,387 You can see we've got the output in the bottom down there. 20 00:00:52,387 --> 00:00:53,600 So far so good, 21 00:00:53,600 --> 00:00:56,100 but let's actually alter this slightly as follows. 22 00:00:56,100 --> 00:00:58,580 I'm going to change the switch statement on line 13. 23 00:00:58,580 --> 00:01:00,630 Instead of switch i multiplied by 10, 24 00:01:00,630 --> 00:01:02,730 just to make that switch i. 25 00:01:02,730 --> 00:01:04,910 Suddenly we've got five compiled errors, 26 00:01:04,910 --> 00:01:06,640 basically one on each of the five case labels, 27 00:01:06,640 --> 00:01:08,840 here as you can see on screen. 28 00:01:08,840 --> 00:01:10,073 Why is that the case? 29 00:01:11,070 --> 00:01:13,360 Required byte found int. 30 00:01:13,360 --> 00:01:16,590 When our switch expression was i multiplied by 10, 31 00:01:16,590 --> 00:01:19,020 the switch variable data type was an int. 32 00:01:19,020 --> 00:01:22,430 And so our case labels were also int, and all was well. 33 00:01:22,430 --> 00:01:25,640 Now what we've done is change the switch variable data type 34 00:01:25,640 --> 00:01:28,560 to a byte where after will lead me through an array of byte 35 00:01:28,560 --> 00:01:30,610 but our case labels are still an int, 36 00:01:30,610 --> 00:01:33,890 because their values exceed the byte valid value range. 37 00:01:33,890 --> 00:01:37,040 So can fix this if I actually change this code slightly now. 38 00:01:37,040 --> 00:01:38,240 Basically adjusting the labels 39 00:01:38,240 --> 00:01:39,690 to be values that are valid bytes. 40 00:01:39,690 --> 00:01:42,210 So I'm just going to copy and paste the code. 41 00:01:42,210 --> 00:01:43,820 Okay so you can see what I've done there now. 42 00:01:43,820 --> 00:01:44,710 Changing those values, 43 00:01:44,710 --> 00:01:47,360 and because the values are now byte valid 44 00:01:47,360 --> 00:01:49,890 so they're actually in the range of a byte 45 00:01:49,890 --> 00:01:52,300 they've no longer got any compilation errors. 46 00:01:52,300 --> 00:01:53,850 Just to confirm we'll run this. 47 00:01:55,670 --> 00:01:56,673 And the code works. 48 00:01:57,840 --> 00:01:59,090 Right so let's go back to the code. 49 00:01:59,090 --> 00:02:00,100 Specifically what I'm going to do 50 00:02:00,100 --> 00:02:02,850 is make a change to the case 104. 51 00:02:02,850 --> 00:02:05,123 If I change that and add a continue. 52 00:02:07,030 --> 00:02:09,820 What does continue mean in a switch statement? 53 00:02:09,820 --> 00:02:11,430 Well actually continue doesn't mean anything 54 00:02:11,430 --> 00:02:12,290 in a switch statement. 55 00:02:12,290 --> 00:02:15,210 It's associated with the encasing for loop, 56 00:02:15,210 --> 00:02:16,090 that we're executing in. 57 00:02:16,090 --> 00:02:17,840 The one starting on line 12. 58 00:02:17,840 --> 00:02:19,563 So let's run the code again. 59 00:02:22,590 --> 00:02:24,140 And you can see we've got a different output 60 00:02:24,140 --> 00:02:25,630 down the bottom now. 61 00:02:25,630 --> 00:02:30,580 So looking at the output, the values 100, 103, 104 62 00:02:30,580 --> 00:02:34,570 they all actually reach the case statement 104 63 00:02:34,570 --> 00:02:36,330 and because of the continue statement 64 00:02:36,330 --> 00:02:39,150 initiated a new iteration of the surrounding loop, 65 00:02:39,150 --> 00:02:41,380 skipping the code after the switch statement. 66 00:02:41,380 --> 00:02:46,363 In other words, down here the system.out.println on line 25. 67 00:02:47,650 --> 00:02:50,170 How would you break out of a loop from a switch statement? 68 00:02:50,170 --> 00:02:52,280 You can't do it with a simple break, can you? 69 00:02:52,280 --> 00:02:53,770 Because a break in a switch statement 70 00:02:53,770 --> 00:02:55,620 is just a break in the switch label. 71 00:02:55,620 --> 00:02:58,880 To break out of a loop from a switch conditional block 72 00:02:58,880 --> 00:03:01,360 you'll need to create a label for your for loop, 73 00:03:01,360 --> 00:03:04,140 which we'll cover in much more detail in the video on loops. 74 00:03:04,140 --> 00:03:05,960 And that's coming up later in the course. 75 00:03:05,960 --> 00:03:08,880 But you're probably already familiar with labels here. 76 00:03:08,880 --> 00:03:10,390 What we'll do is we'll add a label here 77 00:03:10,390 --> 00:03:13,810 and we'll answer the question we asked by changing our code 78 00:03:13,810 --> 00:03:16,793 for the case label 104 and 107. 79 00:03:17,960 --> 00:03:19,630 So what we're gonna do is add a label as I mentioned. 80 00:03:19,630 --> 00:03:21,620 So we'll go back to the code. 81 00:03:21,620 --> 00:03:24,260 We're going to add the label above for loop. 82 00:03:24,260 --> 00:03:25,093 So up here. 83 00:03:26,040 --> 00:03:28,830 Start, I'll just call for. 84 00:03:28,830 --> 00:03:29,663 There's our label. 85 00:03:29,663 --> 00:03:32,360 Now we're gonna change the condition 86 00:03:32,360 --> 00:03:35,010 from continue for our case 104 to a break. 87 00:03:38,010 --> 00:03:40,670 Moving on down for the condition for 107, 88 00:03:40,670 --> 00:03:41,980 we've got a break there. 89 00:03:41,980 --> 00:03:44,360 We're gonna change that to a break. 90 00:03:44,360 --> 00:03:46,680 This time we're gonna use the start_for label 91 00:03:47,580 --> 00:03:49,842 that we added on line 13. 92 00:03:49,842 --> 00:03:51,342 Right, so we run the code now. 93 00:03:54,530 --> 00:03:57,940 So the break in case label 104 prevented any of values 94 00:03:57,940 --> 00:03:59,690 being assigned a value 95 00:03:59,690 --> 00:04:04,690 because the value only occurs in case 107 and case 126. 96 00:04:05,200 --> 00:04:08,930 And the break in case label 107 is the for loop break 97 00:04:08,930 --> 00:04:10,800 and not just the switch statement break. 98 00:04:10,800 --> 00:04:12,790 So we immediately break out of the for loop 99 00:04:12,790 --> 00:04:14,540 without printing another statement. 100 00:04:14,540 --> 00:04:16,410 Now if we added a case statement break 101 00:04:16,410 --> 00:04:21,060 either before or after the break, to find in label 107 102 00:04:21,060 --> 00:04:22,800 we would actually cause a compiler error 103 00:04:22,800 --> 00:04:25,560 indicating one of the other breaks is unreachable. 104 00:04:25,560 --> 00:04:27,320 So as you can see there's many variations 105 00:04:27,320 --> 00:04:28,400 to a switch statement, 106 00:04:28,400 --> 00:04:31,543 and many variables that can lead to compiler errors. 107 00:04:33,300 --> 00:04:35,470 When you see a switch statement on an exam, 108 00:04:35,470 --> 00:04:39,000 examine its location, is it participating in a loop? 109 00:04:39,000 --> 00:04:42,260 Don't let the breaks and continue statements mislead you. 110 00:04:42,260 --> 00:04:45,470 Examine the switch expression, can you determine the type? 111 00:04:45,470 --> 00:04:47,900 Does the type match the case labels? 112 00:04:47,900 --> 00:04:49,450 Is the type valid? 113 00:04:49,450 --> 00:04:53,050 Doubles, floats, longs, booleans are all not valid. 114 00:04:53,050 --> 00:04:56,530 Objects that are not strings or wrappers are also not valid, 115 00:04:56,530 --> 00:04:58,300 remembering e nums are valid. 116 00:04:58,300 --> 00:05:00,570 If the switch expression is a local variable, 117 00:05:00,570 --> 00:05:01,853 has it been initialised? 118 00:05:02,940 --> 00:05:04,130 If it hasn't, 119 00:05:04,130 --> 00:05:06,400 does the switch statement have a default block? 120 00:05:06,400 --> 00:05:09,010 If not, then the answer is compiler error. 121 00:05:09,010 --> 00:05:12,500 Examine the case labels, are they all compiler constants? 122 00:05:12,500 --> 00:05:14,250 Variables are not permitted. 123 00:05:14,250 --> 00:05:17,450 If case blocks do not have breaks, the code falls through, 124 00:05:17,450 --> 00:05:19,590 so multiple blocks could be executed. 125 00:05:19,590 --> 00:05:22,060 And finally, remember that a default label 126 00:05:22,060 --> 00:05:23,210 doesn't have to be the last one 127 00:05:23,210 --> 00:05:25,023 or need to be included at all. 128 00:05:26,134 --> 00:05:28,170 All right so let's end the video here. 129 00:05:28,170 --> 00:05:30,780 In the next one we'll start looking, or look at a quiz 130 00:05:30,780 --> 00:05:32,250 on decision constructs. 131 00:05:32,250 --> 00:05:34,850 Then after the quiz we'll get into loops. 132 00:05:34,850 --> 00:05:36,150 See you in the next video.