Enum in Java

Enum

Enums in Java are a unique type which holds a collection of constants.
Enums can be considered as a special type of java class which can hold constants as well as methods.

How to use Enum?

Enums can be used like a class.

public enum Temperature
{
HIGH,
MEDIUM,
LOW
}

- The above written enum will be saved as Temperature.java and would be compiled in the same way class is compiled.
- When compiler find the word enum it understands that this is not a class but an enum.

when later we need to access it we can access it like this:

Temperature t=Temperature.HIGH;

Let us write a small code to access the enum now.

AccessEnum.java

class AccessEnum 
{
public static void main(String[] args) 
{
Temperature t=Temperature.HIGH;
if(t==Temperature.HIGH)
{
System.out.println("Temperature is High");
}
}
}

Enums can also hold fields as well as methods. 

public enum Temperature
{
HIGH(1),// -----------> will call the constructor and pass value 1
MEDIUM(2),//-------> will call the constructor and pass value 2
LOW(3);//------------> will call the constructor and pass value 3
//A semi colon should be used to mark the end of constants.

public final int i;

Temperature(int i)
{
this.i=i;
}
}

Enums can also contain methods.

public enum Temperature
{
HIGH(1),// -----------> will call the constructor and pass value 1
MEDIUM(2),//-------> will call the constructor and pass value 2
LOW(3);//------------> will call the constructor and pass value 3
//A semi colon should be used to mark the end of constants.

public final int i;

Temperature(int i)
{
this.i=i;
}
       
       public int getI()

      {
        return i;
      }


}

Now let us again modify our AccessEnum.java

class AccessEnum 
{
public static void main(String[] args) 
{
Temperature t=Temperature.HIGH;
if(t==Temperature.HIGH)
{
System.out.println("Temperature is High");
System.out.println(t.getI());
}
}
}

Iterating through Enum

Every enum have got a static method values() which return the array of constants in enum.

for(Temperature t:Temperature.values())
{
System.out.println(t);
}

Facts about Enum

1. Every enum implicitly extends java.lang.Enum.
2. An enum cannot extend any other enum.
3. List of constants in enum should be terminated by a semi-colon(;).
4. If an enum contains constants as well as fields and methods, list of constants should come first followed by the other two.