Java Enums - ¡Inmutable by default!

Enum type with constant-specific class bodies and data

public enum Operation {
	PLUS("+"){
		double apply (double x, double y) { return x + y;}
	},
	
	MINUS("-"){
		double apply (double x, double y) { return x - y;}
	};

	private final String symbol;
	Operation (String symbol){ this.symbol = symbol;}
	@Override public String toString(){ return symbol;}
	abstract double apply (double x, double y);
}

enum type with data and behaviour

public enum Options {
	HELP("tralari", 3),
	FILE("tralara", 1), 
	URL("pichiflu", 2);

	private final String nombre;
	private final int numero;

	Options(String nombre, int numero) {
		this.nombre = nombre;
		this.numero = numero;
	}

	public String nombre() {
		return this.nombre;
	}

	public String nombreCompleto() {
		return this.nombre + String.valueOf(this.numero);
	}
}

Iterables

for (Planet p : Planet.values()){
	p.tralari()
}

Usando EnumSet

public enum Color {
    RED, BLUE, YELLOW, GREEN, ORANGE, PURPLE;

    public static EnumSet<Color> getPrimaryColors() {
        return EnumSet.of(RED, BLUE, YELLOW);
    }
}