In regards to the difference between Java "Properties" and C#' Properties

Question

I worked with C# for a good six months as part of my internship. Something I learned over that internship is the beauty of C# properties, AKA setters and getters. In the beginning of the internship, properties was also a source of my confusion, but using it for awhile, I fell in love with it.

Coming back to Java for classes, I had to bid goodbye to it.

Until.. I started this simple assignment:

My methods and constructors:

private double xCoor;
private double yCoor;

public Point(double xCoor, double yCoor)
{
    this.xCoor = xCoor;
    this.yCoor = yCoor;
}

public void setCoor(double xCoor, double yCoor)
{
    this.xCoor = xCoor;
    this.yCoor = yCoor;
}

public void printCoor()
{
    System.out.println("(" + xCoor + ", " + yCoor + ")");
}

For demonstration, here is my main method:

    Point pointOne = new Point(6.0, 7.0);
    pointOne.printCoor();
    pointOne.setCoor(9.0, 3.0);

    pointOne.xCoor = 9.0;
    pointOne.yCoor = 7.0;

    System.out.println("Java Properties: " + pointOne.xCoor);
    System.out.println("Java Properties: " + pointOne.yCoor);

As you can tell, the top three lines begining with Point pointOne = ..; is the "Java" way to do things. You can see the getter which is in the form of a print statement, and the setter which is in the form of .setCoor(..).

Now, my question is, in Java (I JUST learned) - you can also set the private variables via a properties-like declaration through pointOne.xCoor = .., and of course, get them via the same way with pointOne.xCoor.

I am aware of this discrepancy with C#'s way, in that the name of the property can be manually declared, like so (if it's C#).

public string XCoor
{
    get { return this.xCoor; }
    set { xCoor = value; }
}

Can someone help me understand the difference between the way Java does properties and the C# way?

Answer 1

In java you can not set a private field from another class if there is no public getter and setter methods. Private fields without getter and setter methods can only be set and viewed within the same class.

For example

public class A {
    private int a;
    private int b;
    private int c;
    public int s;

    public A(){
        a=5; // In same class
        b=3; // In same class
        c=7;
        s=9;
    }

    public int sum(){
        return a+b; // I can access a and b directly, because we are in the same class with them.
    }

    public getC(){
        return c; // Other classes can read value of c with this public method
    }

    public setC(int value){
        c=value; // Other classes can set value of c with this public method
    }

}


public class B{
    private A obj = new A(); // 

    public void someMethod(){
        int t = obj.getC(); // this is ok
        int g = obj.s; // this is ok because s is public
        int f = obj.c // compiler error, c is private, i can't see it from another class directly
        int p = obj.a // compiler error, a is private, i can't see it from another class directly
    }
}

Answer 2

Now, my question is, in Java (I JUST learned) - you can also set the private variables via a properties-like declaration through pointOne.xCoor = .., and of course, get them via the same way with pointOne.xCoor.

The difference is that if you ever wanted to have some special behavior happen when xCoor got set, it would be impossible to do in Java, unless you ensured that people always accessed this field through a "getter" and "setter" method:

point.setXCoor(1);

In C#, you could simply change the implementation of the property:

public string XCoor
{
    get { return this.xCoor; }
    set { 
       if(value < 0) 
           throw new Exception("Negative values not allowed");
       xCoor = value; 
    }
}

Another way to put it is that C# properties are just "syntax sugar" for "getXxx()" and "setXxx()" methods, which allow you to avoid having to type "get" and "set" so often. "Auto-properties" (get; set;) are just syntax sugar to avoid having to create your own custom implementation for those getter and setter methods. Behind the scenes, the compiler is actually creating a private field for you, just as you would do for yourself if you wrote get and set methods for the fields on a Java class.

Answer 3

Java has no properties. Think of the Java's getter and setter as the C#'s equivalent
of the property's getter and setter. Think of Java's field as the equivalent of C#'s
field. The fact that C# allows you to declare a property without explicitly specifying
the field, does not mean that the field is not there in C#. If I recall well, in previous
versions of C# you had to declare the fields explicitly (so if you had a property
X you would normally had a backing field say _x). Note also that in C# it is
uncommon to have methods like getX or setX (just because you can do the
same via a property X's getter and setter). If you use such methods, it gets
obvious you're coming into C# from Java :)