Java 中的开关：我可以在案例中包含条件吗？
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Switches in Java: Can I include a condition in a case?
提问by Code123
Here is my code:
这是我的代码：
switch(age) {
case 10:
System.out.println("You are too young to drive.");
break;
case 20:
System.out.println("You can drive!");
break;
default:
System.out.println("Error");
}
What happens if the age is 15? Well, it gives me an error. So I was wondering if it's possible to include a condition within the case. For example,
如果年龄是 15 岁会怎样？好吧，它给了我一个错误。所以我想知道是否可以在案例中包含一个条件。例如，
case (age>=10 && age<=20):
System.out.println("You're still too young to drive...");
break;
I could use an if statement, but I'm wondering if this is possible with a switch.
我可以使用 if 语句，但我想知道这是否可以使用 switch。
回答by Tagir Valeev
回答by MrMadsen
Because of fall-through you can do this:
由于跌倒，您可以这样做：
switch(age){
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
System.out.println("You are too young to drive.");
break;
case 20:
System.out.println("You can drive!");
break;
default:
System.out.println("Error");
}
It is a little more code but it accomplishes the same thing.
这是一个多一点的代码，但它完成了同样的事情。
回答by Elliott Frisch
caseRequires a Constant Expression
case需要常量表达式
No. It's not possible because a casemust be a constant expression. But you could (as you guessed) use an if. Logically, anyone under 20(assuming that's the legal age) is too young to drive.
不。这是不可能的，因为 acase必须是一个常量表达式。但是您可以（如您所料）使用if. 从逻辑上讲，任何低于20（假设这是法定年龄）的人都太年轻而不能开车。
final int drivingAge = 20;
if (age < drivingAge) {
System.out.printf("%d is too young to drive...%n", age);
} else {
System.out.printf("%d is old enough to drive.%n", age);
}
Alternatively
或者
That could be written with ? :conditional operator(aka a ternary expression; notesome people find the ternary difficult to read) like
这可以用? :条件运算符（又名三元表达式；注意有些人发现三元很难阅读）写成
final int drivingAge = 20;
System.out.printf(age < drivingAge ? "%d is too young to drive...%n"
: "%d is old enough to drive.%n", age);
回答by Will
You can't do this in Java. A switch jumps to the casethat matches the value you're switching on. You can't use expressions of ageinside the case. However, you can use something called a "fallthrough" (see hereand search for "fall through").
你不能在 Java 中做到这一点。一个开关跳转到case与您要打开的值匹配的那个。您不能age在case. 但是，您可以使用称为“ fallthrough”的东西（请参阅此处并搜索“fall through”）。
So, for your example, you could do something like:
因此，对于您的示例，您可以执行以下操作：
switch(age)
{
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
System.out.println("You are too young to drive.");
break;
case 20:
case 21:
System.out.println("You can drive!");
break;
default:
System.out.println("Error");
}
However, your problem is best solved with an if.
但是，您的问题最好使用if.
回答by Rishabh Singh
Sadly, it's not possible in Java. You'll have to resort to using if-else statements.You can try this, which is very repetitive.
遗憾的是，这在 Java 中是不可能的。你将不得不求助于使用 if-else 语句。你可以试试这个，这是非常重复的。
switch(age){
case 10: case 11: case 12: case 13: case 14: case 15:
//And So on
System.out.println("You are too young to drive.");
break;
case 20:
System.out.println("You can drive!");
break;
default:
System.out.println("Error");
}
Try if statement
试试 if 语句
public void canDrive(int age){
if(age <= 19){
System.out.println("You are too young to drive.")
}
else{
System.out.println("You can drive!");}
}
