Ever been given a class with lousy documentation, no source code, and little instruction on its use? Welcome to the loosely knit organization of real-world programmers. In many cases, you can resort to reflection to figure out what a class has to offer in lieu of source code, and of course JavaDoc is always helpful. In the case of enumerated types, though, there's a nice built-in feature: the values( ) method. This method provides access to all of the types within an enum.
Invoking the values( ) method on an enum returns an array of all the values in the type:
public void listGradeValues(PrintStream out) throws IOException {
Grade[] gradeValues = Grade.values( );
for (Grade g : Grade.values( )) {
out.println("Allowed value: '" + g + "'");
}
}
This is a nice way to get a quick dump of all the allowed values for a particular enum:
run-ch03: [echo] Running Chapter 3 examples from Java 1.5: A Developer's Notebook [echo] Running GradeTester... [java] Allowed value: 'A' [java] Allowed value: 'B' [java] Allowed value: 'C' [java] Allowed value: 'D' [java] Allowed value: 'F' [java] Allowed value: 'INCOMPLETE'
NOTE
Run this sample with the Ant target "run-ch03".
First, note that type-safety is employed. values( ) doesn't return an array of String valuesinstead it returns an array of Grade instances. In the out.println( ) statement, each Grade has its toString( ) method executed, which in turn does provide a String name for the value. At no point are you working with integer constants or even String valuesthe Grade object hides all these implementation details from you, and allows strict compile-time checking.
...using a for/in loop? Well, you're ahead of mefor/in isn't covered until Chapter 7. Still, for those of you who are curious, you can indeed perform the same iteration with Tiger's new for/in capabilities:
// for/in loop
for (Grade g : grade.values( )) {
out.println("Allowed value: '" + g + "'");
}