java - 是否可以在 Java 中使用此 switch 语句

Question

C++有一个很方便的switch语句，但不知道这是否可能是java

switch(num)
{
   case 1 ... 9:
     do something
     break
   case 10 ... 19:
     do something
     break
   default: something
}

这在java中是否可行，我试过了，但它不起作用，至少不像c ++那样，有没有等价物？

谢谢

Answer 1

Java's switch statement requires you to explicitly list all values that you match (except for the default: clause, of course). If you're doing substantial ranges, it is probably better to use a chain of ifs:

if (num >= 1 && num <= 9) {
    do_something_A
} else if (num >= 10 && num <= 19) {
    do_something_B
} else {
    do_something_C
}

If your real num has side effects (or is plain expensive to compute), evaluate it once and save it to a local variable, then use that local in the chain of tests.

Answer 2

No, it's not possible. Probably the most straightforward equivalent is:

if (num >= 1 && num <= 9)
  doSomething();
else if (num >= 10 && num <= 19)
  doSomethingElse();
else
  doDefault();

Marginal cleanup could be defining an inRange utility function and using it inside the if statements:

boolean inRange(int num, int min, int max) {
    return num >= min && num <= max;
}

...

if (inRange(num, 1, 9))
  doSomething();
else if (inRange(num, 10, 19))
  doSomethingElse();
else
  doDefault();

Answer 3

Java have switch statement, but you have to use it in this way :

switch(num)
{
   case 1:
   case 2:
   case 3:
   case 4:
     //And so far with cases 
     //do something
     break
   case 10:
   case 11:
   case 12:
     //And so far ...
     //do something
     break
   default: something
}

Answer 4

Yes, there is a switch statement in Java. It is in fact quite similar to switch in C++.

However, neither C++ nor Java support ranges in case labels.

For the specific example that you present I would use a series of if statements:

if (num >= 1 && num <= 9) {
  ...
} else if (num >= 10 && num <= 19) {
  ...
} else {
  ...
}

Answer 5

没有 Java 不会，在这种情况下，使用一系列 if-else 语句会更实用。:)

    if(num >= 1 && num < 10) {
        //do something
    } else if(num >= 10 && num < 20) {
        //do something
    } else {
        //do something
    }

Answer 6

您正在谈论的功能实际上并不属于 C++，它是一种语言扩展，例如存在于 GCC 中。但通常在 C++ 范围内使用if...检查else，并且在 Java 中应该使用相同的技术：

if (num >= 1 && num <= 9) {
    //Do something
} else if (num >= 10 && num <= 19) {
    //Do something else
} else {
    //Do something by default
}

Answer 7

No, ranges are not allowed you would need to use an if else structure.