Enums in Java

If you're familiar with C or C++, you may tend to think of enums as just integers. Which they basically are - in those languages, but not in Java.
Java enum is a special kind of class. What's the difference for you as a user?

It you just want a simple enum and don't care about real values behind enum constants, you can go ahead and just do as in old good C (almost, as C syntax is slightly different):

enum Color {RED, GREEN, YELLOW}
 . . .
Colors col = RED;

But if you try to assign an integer value to col, as you could in C, like so:

col = 2;

- the code fails to compile, which is a good thing, as you obviously want your value to be one of the predefined constants.
Well, actually you can't compile this in C++ either, but you can still force the compiler to build it by using a cast like this one:

col = (Color)2;

But that's beside the point. If you want your constants to have specific values, in C you could achieve that like this (note that this is C syntax, which is slightly different from Java):

enum Color {RED=5, YELLOW=10, GREEN=15};

If you want this in Java, you have to take into account that your enum is going to be a special kind of Java class, extending java.lang.Enum. Its syntax is also different from both C / C++ enums and normal Java classes:

enum Color
{
    RED(5), GREEN(10), YELLOW(15);
    private int col;
    private Color(int col) { this.col = col; }
    private int getValue() { return col; }
}

And this is how you use it:

Color c = Color.RED;
System.out.println(c);

which prints out

RED

But you can't just go and assign an integer value to your enum object:

Color c = 5;
System.out.println(c);

because

error: incompatible types: int cannot be converted to Color

There's much more to Java enums, check out these links for more details:

• https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
• http://javarevisited.blogspot.com/2011/08/enum-in-java-example-tutorial.html