Learn java Lesson 11: switch multi branch statements

zyqok 2020-11-13 10:16:53
learn java lesson switch multi


【 Related links 】

Last one : Xiaobaixue Java The first 10 course :if Conditional statements

Next : Xiaobaixue Java The first 12 course :for loop

general programme : Returns a list of

 

【1】switch Semantic analysis

Search from Baidu switch You can learn from this word , He used the verb to change the meaning , To be a noun means to transform .

What is a converter ? Like the plug-in board below , It's actually a simple Converter , The current can enter from the only entrance , And coming out of multiple outlets .

In the program , When a conditional entry may satisfy multiple output situations , Now we can use switch Conditional statements .

【2】switch Conditional sentence format

switch (x) {
case value 1:
// do x = value 1 What happened
break;
case value 2:
// do x = value 1 What happened
break;
// ..... There can be a lot of (n individual )case Sentence block
default:
// It's done x Things that don't satisfy all the above values
break;
}

there x Represents a specific value that may appear , It's like the entrance of the patch panel . You can see switch There are a lot of case scene ,case In English it means " Case study " It means , Like we used to do math problems , There are cases 1, Case study 2, Case study 3 And so on these , It can also be understood in this way , It's like there are multiple outlets for the patch panel .

Every case Then there is a specific value , When it comes to the entrance x Is equal to a case After this value , The code just executes this case The words in it .

Finally, when this case When it's done , Usually you need to write a break( The meaning of the interruption , No further execution ) To interrupt , To keep him from going on , thus ,switch Sentence block can solve the logic of many uncertain situations in life .

【3】 Illustrate with examples

Let's also use dice as an example :

Here's the number of dice :

Let's assume that our points are x spot , Then you can translate it into :

int x = 1;
switch (x) {
case 1:
System.out.println(" Small ");
break;
case 2:
System.out.println(" Small ");
break;
case 3:
System.out.println(" in ");
break;
case 4:
System.out.println(" in ");
break;
case 5:
System.out.println(" Big ");
break;
case 6:
System.out.println(" Big ");
break;
default:
System.out.println(" It's not the normal number of dice ");
break;
}

【4】 Code instructions

The new class Test11, We copy the above code into the main method , And then run :

You can see , When x=1 When , The output is predicted " Small " ;

We will x Change it to 8, This point doesn't belong to 6 The number of face dice , In terms of code , He doesn't belong to any one of them case situation , So we have to go to the last one default Branch .

From the result of the execution , It's exactly what we predicted .

【5】switch Simplified block statements

If switch The multiple case in , Different exist case, But when dealing with the same situation , So at this time , these case It can be written side by side , Share one break; This will simplify the code . for example , above 1 and 2 It's all small , When x=1 and x=2 They all output “ Small ”, So they can write side by side ,“ in ” and “ Big ” Empathy .

such , The above code can be simplified to the following :

int x = 8;
switch (x) {
case 1:
case 2:
System.out.println(" Small ");
break;
case 3:
case 4:
System.out.println(" in ");
break;
case 5:
case 6:
System.out.println(" Big ");
break;
default:
System.out.println(" It's not the normal number of dice ");
break;
}

【5】switch sentence conversion if sentence :

be-all switch Sentence block , Can be transformed into if Sentence block .

For example, above switch Sentence block , It can be transformed into the following if sentence :

if (x == 1 || x == 2) {
System.out.println(" Small ");
} else if (x == 3 || x == 4) {
System.out.println(" in ");
} else if (x == 5 || x == 6) {
System.out.println(" Big ");
} else {
System.out.println(" It's not the normal number of dice ");
}

Both of them are OK , As for what you like to use , It's all right , There's not much difference between the two .

【6】 Sentiment

Now we've learned the binomial operator ,if Conditional statements ,switch sentence , It seems that a lot of time , These usages are interlinked , Can achieve some of the same functions .

We write programs like doing a math problem , There are many ways to solve problems , Some methods are easy to understand , But maybe it's too much , It's too cumbersome , Cause others to watch for most of the day , Maybe it's too wordy ; And some methods may only need to write a few or a dozen lines , The roll is neat , But others may not understand it , I don't even understand , It's not good , It's easy to kill the patience of others .

To make a long story short , You must understand the level of your own code first , If you can't understand it , Then it's over .

In future work , Try to keep the style of the code consistent with your colleagues , If you're good , Then you have to try to catch up with them , Instead of just one person writing a bunch of bad code all the time . If you're a lot better than them , Also don't write some coquettish code everywhere to show how good you are , Make others can't understand , In the end, you're going to get out of your league , This is also a big taboo in our business .

 

 

【 Related links 】

Last one : Xiaobaixue Java The first 10 course :if Conditional statements

Next : Xiaobaixue Java The first 12 course :for loop

general programme : Returns a list of

 

 

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