Use string in switch case in java

Question

I need to change the following if's to a switch-case while checking for a String, to improve the cyclomatic complexity.

String value = some methodx;
if ("apple".equals(value)) {
    method1;
}

if ("carrot".equals(value)) {
    method2;
}

if ("mango".equals(value)) {
    method3;
}

if ("orange".equals(value)) {
    method4;
}

But I am not sure what value I'm going to get.

Solution 1

Java (before version 7) does not support String in switch/case. But you can achieve the desired result by using an enum.

private enum Fruit {
    apple, carrot, mango, orange;
}

String value; // assume input
Fruit fruit = Fruit.valueOf(value); // surround with try/catch

switch(fruit) {
    case apple:
        method1;
        break;
    case carrot:
        method2;
        break;
    // etc...
}

Solution 2

Learn to use else.

Since value will never be equal to two unequal strings at once, there are only 5 possible outcomes -- one for each value you care about, plus one for "none of the above". But because your code doesn't eliminate the tests that can't pass, it has 16 "possible" paths (2 ^ the number of tests), of which most will never be followed.

With else, the only paths that exist are the 5 that can actually happen.

String value = some methodx;
if ("apple".equals(value )) {
    method1;
}
else if ("carrot".equals(value )) {
    method2;
}
else if ("mango".equals(value )) {
    method3;
}
else if ("orance".equals(value )) {
    method4;
}

Or start using JDK 7, which includes the ability to use strings in a switch statement. Course, Java will just compile the switch into an if/else like construct anyway...

Solution 3

Everybody is using at least Java 7 now, right? Here is the answer to the original problem:

String myString = getFruitString();

switch (myString) {

    case "apple":
        method1();
        break;

    case "carrot":
        method2();
        break;

    case "mango":
        method3();
        break;

    case "orange":
        method4();
        break;
}

Notes

• The case statements are equivalent to using String.equals.
• As usual, String matching is case sensitive.
• According to the docs, this is generally faster than using chained if-else statements (as in cHao's answer).

Solution 4

To reduce cyclomatic complexity use a map:

Map<String,Callable<Object>> map = new HashMap < > ( ) ;
map . put ( "apple" , new Callable<Object> () { public Object call ( method1 ( ) ; return null ; } ) ;
...
map . get ( x ) . call ( ) ;

or polymorphism

Solution 5

Just to make concrete emory's answer, the executable code is the following :

  Map<String,Callable<USer>> map = new HashMap<String,Callable<User>>();
  map.put( "test" , new Callable<User> () { public User call (){ return fillUser("test" ); }} ) ;
  map.put( "admin" , new Callable<Utente> () { public Utente call (){  return fillUser("admin" ); }} ) ;

where user is a POJO, and then

  User user = map.get(USERNAME).call();

finally the called method is somewhere :

 private User fillUser(String x){        
        User user = new User();
        // set something in User
        return user;
}

View more solutions