kurz Frage

Frage zur Aufgabe

Gelöst

I don´t get what we've done here with the Keyword return . I haven't seen it in such use before: public MarkTwainBook getBook() { return this; } is it as if we did like this ? : public MarkTwainBook getBook() { return new MarkTwainBook(); } i tried it and i guess i´m wrong , so i would like to know its functionality

Kommentare (4)

Beliebt
Neu
Alt

Du musst angemeldet sein, um einen Kommentar schreiben zu können

Lisa L

Level 47 , Nuremberg, Germany

16 April 2022, 08:39

Lösung

no, return this; returns the current object as this refernces exectly that while return new MarkTwainBook(); would return the refernce to a newly created MarkTwainBook object.

public class Cat {
    public Cat getThisCat() {
        return this;
    }

    public Cat getNewCat() {
        return new Cat();
    }

    public static void main(String[] args) {
        Cat origCat = new Cat();
        System.out.println(origCat == origCat.getThisCat()); // the same cat, same reference, this
        System.out.println(origCat == origCat.getNewCat()); // diff references
    }
}

Sakka Mouid

Level 19 , Hannover, Deutschland

17 April 2022, 00:20

Thanks for the solution ^ ^ . tried to use the compare of references that you used in the explanation to check if it's really the same object in question . i used it in another topic : I

I know that the static keyword is used for memory management . It makes your program memory efficient . But the thing here , each time we declare a new object and initialise it , we get in the output the previous number + 1 , as if the new object takes the place in memory of the previous object ( same reference) . BUT , i get false , this means , it's not as i thought :)

Lisa L

Level 47 , Nuremberg, Germany

17 April 2022, 08:26

new creates new objects... you create three new objects above and they are of course saved in three different locations inside your computers memory. You need to add a method that returns this like

public Counter getThis() {
    return this;
}

then you can create a Counter object in main and compare it to the return value of getThis

Counter counter = new Counter();
boolean isSame = counter == counter.getThis();

So this is the reference to the current object. Here the current object is counter... the object that calls the method.

Guadalupe Gagnon

Level 37 , Tampa, United States

18 April 2022, 14:09

nützlich

@ Sakka static doesn't mean efficient. 'static' members are part of the class and not independent of any object. This is why you can call static methods without first creating an object. See example:

public class Solution {
    static int classInt = 0;
    int objectInt;

    public Solution(){
        objectInt = ++classInt;
    }

    public static void main(String[] args) {
        System.out.println(Solution.classInt); // uses static field (prints 0)
        Solution.printClassInt(); // uses static method (prints 0)
        // Solution.printObjInt(); !!! This line will be an error because method is not static and needs an object

        // here we create an object and print the static field and object field
        Solution obj1 = new Solution();
        Solution.printClassInt(); // static method call (prints 1)
        obj1.printClassInt(); // static method call using object (this is OK, but not good practice)
        obj1.printObjInt(); // method call with object (prints 1)

        Solution obj2 = new Solution(); // create new object
        Solution.printClassInt(); // print static field (prints 2 now)
        obj1.printClassInt(); // print obj1 class fiels (prints 1)

        obj2 = new Solution(); // creates new object for obj2
        Solution obj3 = obj1; // create new variable, set to old object (no new object)

        obj3.printClassInt(); // prints static field (prints 3)
        obj3.printObjInt();  // prints object field (prints 1)
    }

    void printObjInt() {
        System.out.println(objectInt);
    }

    static void printClassInt() {
        System.out.println(classInt);
    }
}

run it and see if you can follow along with the notes that I added.