I declare an enum as :
enum Sex {MALE,FEMALE};
And then, iterate enum as shown below :
for(Sex v : Sex.values()){
System.out.println(" values :"+ v);
}
I checked the Java API but can't find the values() method? I'm curious as to where this method comes from?
API link : https://docs.oracle.com/javase/8/docs/api/java/lang/Enum.html
Run this
for (Method m : sex.class.getDeclaredMethods()) {
System.out.println(m);
}
you will see
public static test.Sex test.Sex.valueOf(java.lang.String)
public static test.Sex[] test.Sex.values()
These are all public methods that "sex" class has. They are not in the source code, javac.exe added them
Notes:
never use sex as a class name, it's difficult to read your code, we use Sex in Java
when facing a Java puzzle like this one, I recommend to use a bytecode decompiler tool (I use Andrey Loskutov's bytecode outline Eclispe plugin). This will show all what's inside a class
The method is implicitly defined (i.e. generated by the compiler).
From the JLS:
In addition, if
E
is the name of anenum
type, then that type has the following implicitly declaredstatic
methods:/** * Returns an array containing the constants of this enum * type, in the order they're declared. This method may be * used to iterate over the constants as follows: * * for(E c : E.values()) * System.out.println(c); * * @return an array containing the constants of this enum * type, in the order they're declared */ public static E[] values(); /** * Returns the enum constant of this type with the specified * name. * The string must match exactly an identifier used to declare * an enum constant in this type. (Extraneous whitespace * characters are not permitted.) * * @return the enum constant with the specified name * @throws IllegalArgumentException if this enum type has no * constant with the specified name */ public static E valueOf(String name);
Source: Stackoverflow.com