why we are using enums in Java?

[manish.anchan]

what is the use of enum and when it can be more useful?:confused:

[r035198x]

What do the books/tutorials say?

[manish.anchan]

Actually in tutorial they have mentioned that when ever we need fixed set of constants we can apply it. But my query is when arrays are there, why do we need that. what makes it more essential.

[JosAH]

what is the use of enum and when it can be more useful?:confused:

Enums are type safe constants; imagine ints like this:

// in one class. say BorderLayout:
public static final int NORTH= 0;
public static final int EAST= 1;
public static final int SOUTH= 2;
public static final int WEST= 3;

and some other unrelated ints:

// in you class, modeling a card:
public static final int SPADES= 0;
public static final int HEARTS= 1;
public static final int DIAMONDS= 2;
public static final int CLUBS= 3;

There is nothing that prevents you from using an int from the first class and use it in your second class. Your code will be a mess before you know it but the compiler cannot detect the (ab)use of those ints. Two separate Enums forbid this madness.

kind regards,

Jos

[gcampton]

And for some more random uses...

enum Apple { 
  A(10), B(9), C, D(15), E(8); 
 
  private int price; // price of each apple 
 
  // Constructor 
  Apple(int p) { price = p; } 
 
  // Overloaded constructor 
  Apple() { price = -1; } 
 
  int getPrice() { return price; } 
}

[manish.anchan]

Thank u very much josh and
gcampton . It really gave me good knowledge.:)

[Tolls]

The Sun guide to Enums.

[FON]

Here is why enums are beeter than classic java constants:

Java: Enums

Think of it as special class definition
which gives you power to represent set of data in easy manner
and control and use is it easily.

JosAH made good point about enforcing type safety in your code.
Just define your special class as enum, add some entries
and use it it some other class as field.

I use it often to represent status of some transaction in my sistem.

//---enumerator for Transaction status .
	public enum Status{

		ER1_TR_OK	(10,"Transaction OK"),
		ER2_LIMIT	(16,"Over transaction limit."),
		ER3_INTERNAL	(21,"Internal error");

		private int errorCode;
		private String errorDesc;

		private Status (int i, String s){
			this.errorCode = i;
			this.errorDesc = s;
			
		}

	}///

I put this Status as private filed of my Transaction class.

Now, user can never set Transaction Status
on some, lets say integer value,
that is not defined in enum above,
user must use enum!

Also representation is very clear to him
because of descriptive name "ER1_TR_OK"
not just some int value that is mapped somewhere in code
to something more meaningful.


hope this will clear things up for you ;)