Java 7 for Absolute Beginners

CHAPTER 3 ■ DATA TYPES

■ Caution Do not write collections of constants this way. They can be compared to int values, and that's almost

certain to be the wrong thing to do. That's why Java has enumerations.The enumeration value, Direction.NORTH,

can't be treated as an integer (not even by accident), whereas the constant, NORTH, can be. Also, constants are

static and final (and often public). Enumerations remove the need for those modifiers, which gives us greater

flexibility when using enumerations.

Each enum is actually a class. (You might have noticed that its declaration syntax is similar to a class.)

All enum objects implicitly extend java.lang.Enum. That lets us make more meaningful enums than just

lists of constants. To continue with our example, we can set the degrees for each direction, as shown in

Listing 3-13.

Listing 3-13. Enum with more information

public enum Direction {

NORTH (0),

EAST (90),

SOUTH (180),

WEST (270);

private final int degrees;

Direction(int degrees) {

this.degrees = degrees;

}

public int getDegrees() {

return degrees;

}

}

From there, we can write code to get the additional information associated with each value in the

enumeration, as shown in Listing 3-14.

Listing 3-14. Getting details from an enum

for (Direction d : Direction.values()) {

System.out.println(d + " is " + d.degrees + "degrees.");

}

We can also write methods that work with the enumeration's values. For example, we can write a

method that, given a direction in degrees, tells you which cardinal direction is closest. Listing 3-15 shows

one way to write such a method.