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javaenumsconstants
whirlwin
whirlwin

Reputation: 16551

Why are constants in Java the way they are?

I have read about Java enums and use them regularly. However, I don't understand why e.g JFrame.EXIT_ON_CLOSE returns an int.

Considering http://download.oracle.com/javase/1.5.0/docs/guide/language/enums.html;

// int Enum Pattern - has severe problems!
public static final int SEASON_WINTER = 0;
public static final int SEASON_SPRING = 1;
public static final int SEASON_SUMMER = 2;
public static final int SEASON_FALL   = 3;

Not typesafe - Since a season is just an int you can pass in any other int value where a season is required, or add two seasons together (which makes no sense).

JFrame.EXIT_ON_CLOSE returns 3, while JFrame.HIDE_ON_CLOSE returns 1, which means three of the latter equals the first.

Why is it implemented this way?

Upvotes: 1

Views: 213

Answers (4)

Erik
Erik

Reputation: 91330

Java didn't have enums until 1.5 - most of these constants were introduced earlier, and if they were changed to enums Sun would've broken a lot of existing code.

Upvotes: 14

Peter Knego
Peter Knego

Reputation: 80350

The link that you provided says:

In prior releases, the standard way to represent an enumerated type was
the int Enum pattern:

// int Enum Pattern - has severe problems!
public static final int SEASON_WINTER = 0;
public static final int SEASON_SPRING = 1;
etc...

Java Swing (JFrame) was available much earlier.

Upvotes: 1

Isaac Truett
Isaac Truett

Reputation: 8874

Enums are a recent addition to Java. Changing all of the old integer constants to enums would've broken a lot of existing Java code.

Upvotes: 3

Brendan Long
Brendan Long

Reputation: 54312

Those constants were probably added to the standard library before enums were added to the language. Enums were added in Java 1.5. To maintain backwards compatibility, they left old constants how they were.

Upvotes: 3

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