静态valueOf（）方法有什么意义？ （枚举）

Question

I am learning about enumerations and I don't understand the purpose this method serves.

Example:

enum Fruits{
    apple, pear, orange
}

class Demo{
    f = Fruits.valueOf("apple");  //returns apple... but I had to type it!
                                 // so why wouldn't I save myself some time
                                 // and just write: f = Fruits.apple; !?

}    

Answer 1

The point of valueOf method is to provide you a way of obtaining Fruits values presented to your program as String s - for example, when values come from a configuration file or a user input:

String fruitName = input.next();
Fruits fruit = Fruits.valueOf(fruitName);

Above, the name of the fruit is provided by end-user. Your program can read and process it as an enum , without knowing which fruit would be supplied at run-time.

Answer 2

I agree with @dasblinkenlight, You can use Enum.valueOf() method If you have some runtime input.

String input="apple" //It may be passed from some where
Fruits fruit = Fruits.valueOf(input);  // Here you will get the object of type Fruits

One more thing I want to add here, If the enum doesn't exist for this input, then It valueOf() method will throw a Runtime exception, instead of returning null. The exception will be:

Exception in thread "main" java.lang.IllegalArgumentException: No enum constant