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enum

TUSHAR KADAM answered on November 22, 2022 Popularity 2/10 Helpfulness 8/10

answer enum

enum

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==Enum in Java==
-Enum is a data type that contains a 'fixed set of constants'.
-it can be days of weeks(SUNDAY,MONDAY...SATURDAY), directions(NORTH,SOUTH,
EAST,WEST), colors(RED,YELLOW,BLUE) etc, --> in CAPITAL letters.

=declaration of enum in java-
-can be done inside class or outside class, but not inside method.
-eg. @outside of class
//Color.java
enum Color{
    RED,
    GREEN,          //we can declare main method inside enum also & we can run
    BLUE;           //as enum file directly from command prompt.
}                   // >javac Color.java  >java Color
//Main.java
public class Main{
    public static void main(String[] args)
    {
        Color c1 = Color.RED;
        System.out.println(c1);
    }
}

-eg. @inside a class
//Main.java
public class Main{
    
    enum Color{
    RED,
    GREEN,
    BLUE;
    }

    public static void main(String[] args)
    {
        Color c1 = Color.RED;
        System.out.println(c1);
    }
}

=Note
-Every enum is internally implemented by using class
-Every enum constant represents an object of type enum.
//the above enum color will be internally converted as-
final class Color extends Enum
{
    public static final Color RED = new Color();
    public static final Color GREEN = new Color();
    public static final Color BLUE = new Color();
}

=Enum and inheritance-
-all enums implicitly extends 'java.lang.Enum' class
-as a class can only extend one parent in java, enum cannot extend anything else
-toString() method is overriden in java.lang.Enum class, which returns enum constant name
-enum can implement many interfaces.

=values() and ordinal() methods:
-these methods are present inside java.lang.Enum
-'values()' mehtod return all values present inside enum
-'ordinal()' method, used to find constant's index (order is important in enums)

//inside Test class we have enum Color
//in main method of Test class-
    Color arr[] = Color.values(); //calling values
    for(Color col : arr)
    {
        System.out.println(col+" at index "+ col.ordinal()); //calling ordinal
    }
//output- RED at index 0
//        GREEN at index 1

-----------------------------------------------------------------------------------

=method inside an enum
-//Item.java
public enum Item{
    SUGER,
    RICE{ //overwritten info method for rice only
            public void info(){
                System.out.println("This is Rice");
            }
    },
    SALT;
    
    public void info(){
        System.out.println("This is grocery item");
    }
}
-//Main.java
public class Main{
    public static void main(String[] args)
    {
        Item[] itr = Item.values();
        
        for(Item item : itr)
        {
            item.info(); //op- each time "This is grocery item" is printing
                        //but for RICE, due to overwritten method, "This is Rice" is printing
        }
    }
}

=constructor inside enum-
-it is executed separately for each enum constant at the time of enum class loading
-we can't create enum objects explicitly and hence we can't invoke enum constructor directly.
-constructor of enum type is private(if you don't declare private, compiler internally creates private constructor)
enum Season{
    WINTER(10),SUMMER(20);
    
    private int value;
    
    Season(int value) //constructor, compiler will add 'private' type prior Season.
    {
        this.value=value;
    }
}

-------------------------------------------------------------------------------

-refer city and Enum in switch case from assignment pages.

-------------------------------------------------------------------------------

Popularity 2/10 Helpfulness 8/10 Language java

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Tags: java

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Contributed on Nov 22 2022

TUSHAR KADAM

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