问题
The program below functions as necessary but how do I reduce the amount of if statements. I have been told that if your function contains 2 or more if statements then your doing it wrong. Any suggestions? I've tried using switch statements but that hasn't worked because the case can't be a boolean.
for(int i = 1; i < 100; i++)
{
if(i % 10 == 3)
{
System.out.println("Fizz" + "(" + i + ") 3%10");
}
if(i / 10 == 3)
{
System.out.println("Fizz" + "(" + i + ") 3/10");
}
if(i % 10 == 5)
{
System.out.println("Buzz" + "(" + i + ") 5%10");
}
if(i / 10 == 5)
{
System.out.println("Fizz" + "(" + i + ") 5/10");
}
if(i / 10 == 7)
{
System.out.println("Fizz" + "(" + i + ") 7/10");
}
if(i%10 == 7)
{
System.out.println("Woof" + "(" + i + ") 7%10");
}
if(i % 3 == 0)
{
System.out.println("Fizz" + "(" + i + ") 3%==0");
}
if(i % 5 == 0)
{
System.out.println("Buzz" + "(" + i + ")5%==0");
}
if(i % 7 == 0)
{
System.out.println("Woof" + "(" + i + ")7%==0");
}
if( (i % 7 !=0 ) && (i % 3 !=0 ) && (i % 5 !=0 )
&& (i % 10 !=3) && (i % 10 !=5 ) && (i%10 !=7 ) )
System.out.println(i);
}
回答1:
How about creating a method for the cases:
public void printIfMod(int value, int mod){
if (value % 10 == mod)
System.out.println(...);
}
public void printIfDiv(int value, int div){
if (value / 10 == div)
System.out.println(...);
}
Then instead of a bunch of if you have a set of calls the the two methods. You might even create a single method that calls both of the above.
public void printIf(int value, int div){
printIfMod(value, div);
printIfDiv(value, div);
}
for(int i = 1; i < 100; i++) {
printIf(i, 3);
printIf(i, 5);
....
}
In the above code the number of ifs is less of an issue to me than the amount of repeated code.
回答2:
Here's a slight improvement using two switch statements
switch(i / 10){
case 3: // do something
break;
case 5: // do something else
break;
case 7: // do something else
break;
}
switch(i % 10){
case 3: // do something
break;
case 5: // do something else
break;
case 7: // do something else
break;
}
Unfortunately you'll need one switch statement per divisor.
Alternatively, you can embrace OOP and come up with an abstraction like this:
public abstract class Processor {
private final int divisor;
private final int result;
private final boolean useDiv; // if true, use /, else use %
public Processor(int divisor, int result, boolean useDiv) {
this.divisor = divisor;
this.result = result;
this.useDiv = useDiv;
}
public final void process(int i){
if (
(useDiv && i / divisor == result)
|| (!useDiv && i % divisor == result)
){
doProcess(i);
}
}
protected abstract void doProcess(int i);
}
Sample usage:
public static void main(String[] args) {
List<Processor> processors = new ArrayList<>();
processors.add(new Processor(10, 3, false) {
@Override
protected void doProcess(int i) {
System.out.println("Fizz" + "(" + i + ") 3%10");
}
});
// add more processors here
for(int i = 1; i < 100; i++){
for (Processor processor : processors) {
processor.process(i);
}
}
}
回答3:
Generally speaking, it's true that code that has a lot of if statements looks suspicious. Suspicious doesn't necessarily mean wrong. If the problem statement has disjoint conditions to check for (i.e. you can't group them) then you have to do them independently like you're doing.
In your case, you're having to check for divisibility without being able to infer one from the other (i.e. if x is divisible by 7, it doesn't mean it's also divisible by 5, etc...). All the numbers you are using have been purposely chosen prime so this is why you're getting into this.
If for example they had said, check for divisibility by 2, 3, and 6. Then you could first check for 6 because then you could also imply divisibility by 2 and 3. Or vice-versa, check by 2 and 3 and imply that it's also divisible by 6. If all the numbers are prime, then you just can't imply. So you're code has to check for everything individually.
One positive side effect is it makes your intent easy to read in your code (because it's all explicit).
My two cents on this...
回答4:
Enums are a good fit here. They allow you to encapsulate the functionality in one location rather than spreading it throughout your flow control.
public class Test {
public enum FizzBuzz {
Fizz {
@Override
String doIt(int n) {
return (n % 10) == 3 ? "3%10"
: (n / 10) == 3 ? "3/10"
: (n / 10) == 5 ? "5/10"
: (n / 10) == 7 ? "7/10"
: (n % 3) == 0 ? "3%==0"
: null;
}
},
Buzz {
@Override
String doIt(int n) {
return (n % 10) == 5 ? "5%10"
: (n % 5) == 0 ? "5%==0"
: (n / 10) == 3 ? "3/10"
: (n / 10) == 5 ? "5/10"
: (n / 10) == 7 ? "7/10"
: null;
}
},
Woof {
@Override
String doIt(int n) {
return (n % 10) == 7 ? "7%10"
: (n % 7) == 0 ? "7%==0"
: null;
}
};
// Returns a String if this one is appropriate for this n.
abstract String doIt(int n);
}
public void test() {
// Duplicates the posters output.
for (int i = 1; i < 100; i++) {
boolean doneIt = false;
for (FizzBuzz fb : FizzBuzz.values()) {
String s = fb.doIt(i);
if (s != null) {
System.out.println(fb + "(" + i + ") " + s);
doneIt = true;
}
}
if (!doneIt) {
System.out.println(i);
}
}
// Implements the game.
for (int i = 1; i < 100; i++) {
boolean doneIt = false;
for (FizzBuzz fb : FizzBuzz.values()) {
String s = fb.doIt(i);
if (s != null) {
if ( doneIt ) {
System.out.print("-");
}
System.out.print(fb);
doneIt = true;
}
}
if (!doneIt) {
System.out.print(i);
}
System.out.println();
}
}
public static void main(String args[]) {
try {
new Test().test();
} catch (Throwable t) {
t.printStackTrace(System.err);
}
}
}
回答5:
I had started to write an answer involving code, but many, many people beat me to it. The one thing I would say which hasn't been mentioned yet is that this particular code metric you're referring to is called cyclomatic complexity and isn't a horrendously bad thing.
In short it refers to the number of different paths that a method could take when it's executed, and while it's quite high in the code snipped that you posted, and there are lots of good tips/solutions to reducing it that have been suggested, personally I would argue that even in it's current form, the code is very readable - which is a bonus. It can be reduced a fair amount and still be readable, but my point is that metrics like that aren't everything, and sometimes it can be simpler to have lots of if statements because it's more readable - and readability reduces the likelihood of making mistakes, and makes debugging much easier
Oh, and I would replace this last section:
if( (i % 7 !=0 ) && (i % 3 !=0 ) && (i % 5 !=0 )
&& (i % 10 !=3) && (i % 10 !=5 ) && (i%10 !=7 ) )
System.out.println(i);
By using a boolean flag such as replaced = true whenever any of the replacement statements are called, then the above statement collapses to:
if (!replaced)
System.out.println(i);
回答6:
I would argue, that you're asking the wrong question. The question I think you should ask is: "How can I rewrite this code so that it is more easily understood by a human?"
The creed "eliminate if statements" is a general idea to accomplish this, but it depends heavily on the context.
The sad fact is that many of the answers obfuscate this very simple algorithm in the guise of "making it simpler." Never introduce an object to eliminate a couple of if statements. In my work, most code is maintained by people that understand far less about the architecture, math and code than the original author, so to introduce additional constructs and complexity to reduce the code from 50 physical lines to 30 physical lines, but makes it 4 times more difficult to understand is not a win.
回答7:
Your code is repetitive. Refactor it using loops for your:
for (int i = 1; i < 100; i++) {
boolean found = false; // used to avoid the lengthy test for "nothing found"
for (int j = 3; j <= 7; j += 2) { // loop 3, 5, 7
if (i % 10 == j) {
System.out.println("Fizz" + "(" + i + ") "+j+"%10");
found = true;
}
if (i / 10 == j) {
System.out.println("Fizz" + "(" + i + ") "+j+"/10");
found = true;
}
if (i % j == 0) {
System.out.println("Fizz" + "(" + i + ") "+j+"%==0");
found = true;
}
}
if (!found) {
System.out.println(i);
}
}
回答8:
You can create multiple switch:
switch (i/10) {
case 3:
System.out.println("Fizz" + "(" + i + ") 3/10");
break;
case 5:
System.out.println("Fizz" + "(" + i + ") 5/10");
break;
case 7:
System.out.println("Fizz" + "(" + i + ") 7/10");
break;
default:
break;
}
switch (i%10) {
case 3:
System.out.println("Fizz" + "(" + i + ") 3%10");
break;
case 5:
System.out.println("Buzz" + "(" + i + ") 5%10");
break;
case 7:
System.out.println("Woof" + "(" + i + ") 7%10");
break;
default:
break;
}
The other case still have to use if statement.
Oracle added switch statement that used String in Java 7. Maybe boolean switch statement will come later.
回答9:
public class Test
{
public static void main(String[] args)
{
final int THREE = 3;
final int FIVE = 5;
final int SEVEN=7;
final int ZERO = 0;
for (int i = 1; i < 100; i++)
{
modOperation("Fizz", i, THREE);
divideOperation("Fizz", i, THREE);
modOperation("Fizz", i, FIVE);
divideOperation("Buzz", i, FIVE);
modOperation("Woof", i, SEVEN);
divideOperation("Fizz", i, SEVEN);
modOperation("Fizz", i, ZERO);
divideOperation("Fizz", i, ZERO);
}
}
private static void divideOperation(String sound, int i, int j)
{
if (i / 10 == j) // you can add/expand one more parameter for 10 and later on 3 in this example.
{
System.out.println(sound + "(" + i + ") "+j+"/10");
}
}
private static void modOperation(String sound, int i, int j)
{
if (i % 10 == j)
{
System.out.println(sound + "(" + i + ") "+j+"%10");
}
}
}
So now you have less if
来源：https://stackoverflow.com/questions/16669753/how-to-reduce-if-statements