Java enum examples

Simple enum. The ; after the last element is optional, when this is the end of enum definition.

public enum Color {
 WHITE, BLACK, RED, YELLOW, BLUE;  //; is optional
}

Enum embedded inside a class. Outside the enclosing class, elements are referenced as Outter.Color.RED, Outter.Color.BLUE, etc.

public class Outter {
 public enum Color {
   WHITE, BLACK, RED, YELLOW, BLUE
 }
}

Enum that overrides toString method. A semicolon after the last element is required to be able to compile it. More details on overriding enum toString method can be found here.

public enum Color {
 WHITE, BLACK, RED, YELLOW, BLUE;  //; is required here.

 @Override public String toString() {
   //only capitalize the first letter
   String s = super.toString();
   return s.substring(0, 1) + s.substring(1).toLowerCase();
 }
}

Enum with additional fields and custom constructor. Enum constructors must be either private or package default, and protected or public access modifier is not allowed. When custom constructor is declared, all elements declaration must match that constructor.

public enum Color {
 WHITE(21), BLACK(22), RED(23), YELLOW(24), BLUE(25);

 private int code;

 private Color(int c) {
   code = c;
 }

 public int getCode() {
   return code;
 }

Enum that implements interfaces. Enum can implement any interfaces. All enum types implicitly implements java.io.Serializable, and java.lang.Comparable.

public enum Color implements Runnable {
 WHITE, BLACK, RED, YELLOW, BLUE;

 public void run() {
   System.out.println("name()=" + name() +
       ", toString()=" + toString());
 }
}

A sample test program to invoke this run() method:

for(Color c : Color.values()) {
 c.run();
}

Or,

for(Runnable r : Color.values()) {
 r.run();
}