Enum

 package main;

public enum Transport {

    PLANE,
    TRAIN,
    AUTOMOBILE
}

package main;

public class Main {

    public static void main(String[] args) {
        Transport tp = Transport.PLANE;

        if(tp == Transport.PLANE){
            System.out.println("plane...");
        }
    }
}
package main;

public class Main {

    public static void main(String[] args) {
        Transport tr = Transport.TRAIN;
        foo(tr);
    }

    public static void foo(Transport transport) {
        if(transport == Transport.AUTOMOBILE) {
            System.out.println("automobile");
        } else if(transport == Transport.TRAIN) {
            System.out.println("train");
        } else {
            System.out.println("plane");
        }
    }
}
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Arxa planda ne baw verir?
package main;

public enum Emeliyyat {
    TOPLA('+'),
    CIX('-'),
    VUR('*'),
    BOL('/');

    private char c;

    Emeliyyat(char c) {
        this.c = c;
    }

    public char getOperationSymbol() {
        return this.c;
    }

    public double hesabla(double a, double b) {
        if (c == '+') {
            return a + b;
        }
        return -1;
    }
}
package main;

public final class Emeliyyat2 {

    public static final Emeliyyat2 TOPLA = new Emeliyyat2('+');
    public static final Emeliyyat2 CIX = new Emeliyyat2('-');
    public static final Emeliyyat2 VUR = new Emeliyyat2('*');
    public static final Emeliyyat2 BOL = new Emeliyyat2('/');

    private char c;

    Emeliyyat2(char c) {
        this.c = c;
    }

    public char getOperationSymbol() {
        return this.c;
    }

    public double hesabla(double a, double b) {
        if (c == '+') {
            return a + b;
        }
        return -1;
    }
}

* Emumlar-dan extend etmek olmur! Cunki finaldir.

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enum-lar by default public, static ve final-dir. 
enum-larin constructor-lari private-dir.
enum-lar implicitly final-dir, yeni extend oluna bilmezler