多态，找到get的类型

Question

I have a question about polymorphism.

I have a parent Object Case:

public class Case {

//a constructor
//some attributes
//some getters and setters

}

Then a child class:

public class CaseNorm extends Case {
public CaseNorm(//some attributes) {
        super(//some attributes);
    }
}

In my parent class Object, I have an attribute:

private Case nextCase;

But next case can have a type, caseNorm or other child class from Case.

Then in a main class I have to get the case and set this in a variable with the correct type. For example

 public class Labyrinthe {

    public static void main(String[] args) {
        Case case1 = new Case(//some attributes);
//set Next Case, who can be a type of caseNorm, caseHyp, caseHym, etc.
    }

}

I want now to get case1, but with the correct type. How can I do that?

EDIT:

I try to explain my conception, to better understand my question.

I have a case class, that a parent case. This class model a square. Then it has child who specialises this square. CaseNorm (for a normal square, no color, etc), another can be caseHyp (for a red square with a border), etc.

Each case has a number and a position. I want to get the next case, if the actual case is 1, nextCase will be the case 2 (who can be a CaseNorm, or a CaseHyp, etc). I need to know in my application, which type is nextCase.

EDIT2:

It seems that I'm again not clear. I try to be more.

public class Case {

    private int numeroCase;
    private int posX;
    private int posY;
    private int taille;
    private int ligne;
    private int colonne;

    public Case(int numeroCase, int posX, int posY, int taille, int nbLignes, int nbColonnes) {
        this.numeroCase = numeroCase;
        this.posX = posX;
        this.posY = posY;
        this.taille = taille;
        this.ligne = numeroCase / nbColonnes+1;
        this.colonne = numeroCase % nbColonnes+1;
    }

    public int getNumeroCase() {
        return numeroCase;
    }

    public void setNumeroCase(int numeroCase) {
        this.numeroCase = numeroCase;
    }

    public int getPosX() {
        return posX;
    }

    public void setPosX(int posX) {
        this.posX = posX;
    }

    public int getPosY() {
        return posY;
    }

    public void setPosY(int posY) {
        this.posY = posY;
    }

    public int getTaille() {
        return taille;
    }

    public void setTaille(int taille) {
        this.taille = taille;
    }

    public int getLigne() {
        return ligne;
    }

    public void setLigne(int ligne) {
        this.ligne = ligne;
    }

    public int getColonne() {
        return colonne;
    }

    public void setColonne(int colonne) {
        this.colonne = colonne;
    }
}

Subclass:

public class CaseMur extends Case {
    private Color color = Color.BLACK;
     private Color BorderColor = Color.WHITE;

    public CaseMur(int numeroCase, int posX, int posY, int taille) {
        super(numeroCase, posX, posY, taille);
    }

    public Color getColor() {
        return color;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public Color getBorderColor() {
        return BorderColor;
    }

    public void setBorderColor(Color BorderColor) {
        this.BorderColor = BorderColor;
    }

}

CLASS TO SCREEN:

public class Terrain {

    private int nbColonnes;
    private int nbLignes;
    private int largeurCarre;
    private ArrayList<Case> cases = new ArrayList<Case>();
    private Case caseActuelle;
    private Object caseSuivanteDroite; //next right case
    private Object caseSuivanteGauche; //next left case
    private Object caseSuivanteHaut; //next up case
    private Object caseSuivanteBas; //next bottom case

    public Terrain() {
        constructionStatiqueTerrain();
    }

    private void constructionStatiqueTerrain() {
        this.nbColonnes = 7;
        this.nbLignes = 5;
        this.largeurCarre = 40;

        construitCases();
        caseDebut(1);
        caseFin(24);
        caseMur(12);
//        caseMur(17);caseActuelle.getColonne()
        caseMur(22);
    }

    public Object getCaseSuivanteDroite() {
        return caseSuivanteDroite;
    }

    public void setCaseSuivanteDroite(Case caseActuelle) {
        if (caseActuelle.getColonne() < nbColonnes && !cases.get(caseActuelle.getNumeroCase() + 1).getClass().equals(CaseMur.class)) {
            this.caseSuivanteDroite = cases.get(caseActuelle.getNumeroCase() + 1);
        } else {
            this.caseSuivanteDroite = null;
        }
    }

    public Object getCaseSuivanteGauche() {
        return caseSuivanteGauche;
    }

    public void setCaseSuivanteGauche(Case caseSuivanteGauche) {
        if (caseActuelle.getColonne() != 1 && !cases.get(caseActuelle.getNumeroCase() - 1).getClass().equals(CaseMur.class)) {
            this.caseSuivanteGauche = cases.get(caseActuelle.getNumeroCase() - 1);
        } else {
            this.caseSuivanteGauche = null;
        }
    }

    public Object getCaseSuivanteHaut() {
        return caseSuivanteHaut;
    }

    public void setCaseSuivanteHaut(Case caseSuivanteHaut) {
        if (caseActuelle.getLigne() != 1 && !cases.get(caseActuelle.getNumeroCase() - nbColonnes).getClass().equals(CaseMur.class)) {
            this.caseSuivanteHaut = cases.get(caseActuelle.getNumeroCase() - nbColonnes);
        } else {
            this.caseSuivanteHaut = null;
        }
    }

    public Object getCaseSuivanteBas() {
        return caseSuivanteBas;
    }

    public void setCaseSuivanteBas(Case caseSuivanteBas) {
        if (caseActuelle.getLigne() < nbLignes && !cases.get(caseActuelle.getNumeroCase() + nbColonnes).getClass().equals(CaseMur.class)) {
            this.caseSuivanteBas = cases.get(caseActuelle.getNumeroCase() + nbColonnes);
        } else {
            this.caseSuivanteBas = null;
        }
    }

    public void setCaseActuelle(int numCase) {
        this.caseActuelle = new Case(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre, nbLignes, nbColonnes);
        setCaseSuivanteDroite(caseActuelle);
        setCaseSuivanteGauche(caseActuelle);
        setCaseSuivanteHaut(caseActuelle);
        setCaseSuivanteBas(caseActuelle);
    }

    public Case getCaseActuelle() {
        return this.caseActuelle;
    }

    public void caseNormale(int numCase) {
        numCase--;
        cases.set(numCase, new CaseNormale(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre));
    }

    private void caseMur(int numCase) {
        numCase--;
        cases.set(numCase, new CaseMur(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre));
    }

    public void caseDebut(int numCase) {
        numCase--;
        cases.set(numCase, new CaseDebut(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre));
        this.caseActuelle = new Case(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre, nbLignes, nbColonnes);
        this.caseSuivanteDroite = cases.get(numCase + 1);
    }

    private void caseFin(int numCase) {
        numCase--;
        cases.set(numCase, new CaseFin(numCase, cases.get(numCase).getPosX(), cases.get(numCase).getPosY(), largeurCarre));
    }

    private void construitCases() {
        int numeroCase = 1;
        for (int i = 0; i < nbLignes; i++) {
            for (int j = 0; j < nbColonnes; j++) {
                addCase(new CaseNormale(numeroCase, j * largeurCarre, i * largeurCarre, largeurCarre));
                numeroCase++;
            }
        }
    }

    public ArrayList<Case> getCases() {
        return cases;
    }

    public void addCase(Case case1) {
        cases.add(case1);
    }

    public int getNbColonnes() {
        return nbColonnes;
    }

    public void setNbColonnes(int nbColonnes) {
        this.nbColonnes = nbColonnes;
    }

    public int getNbLignes() {
        return nbLignes;
    }

    public void setNbLignes(int nbLignes) {
        this.nbLignes = nbLignes;
    }

    public int getLargeurCarre() {
        return largeurCarre;
    }

    public void setLargeurCarre(int largeurCarre) {
        this.largeurCarre = largeurCarre;
    }

}

In the getCaseSuivanteGauche method, I have to return a Object case, I want to return a case and the use so:

Main class:

Terrain terrain = new Terrain();
terrain.getCaseSuivanteBas().getColor();

but getCaseSuivantBas return an Object or a Case if I change Object by case, and then I cannot catch the CaseNormal methods.

Answer 1

Case is already a "correct" type.

You need to use the constructor of the concrete type that you want when creating an object like new CaseNorm(attribute1, attribute2, attribute3) . You don't need to know the type CaseNorm later when using the object. So, you can assign the object to a variable with type Case and you can pass the object to code that does not know what kind of Case the object is. This is what polymorphism is about. There is a common way to use Case s and the actual implementation of them can vary (by overriding concrete methods or implementing abstract methods).

Answer 2

You're not being really clear in your question.

Given the following class:

class Case {
    // some variables
    private Case nextCase;
    public Case(constructorarg1, arg2, arg3, Case theNextCase) {
        // assign arguments to variables
        nextCase = Case;
}

And there are multiple subtypes of Case ( SpecialCase , CoolCase , CaseInARedDress ).

Your constructor should assign the nextCase... or there should be some setter.

The actual type which is being used is not important, as long as it is a subtype of Case . This subtyping allows you to treat any subtype without knowing it's actual type.

Are you asking something different? If so, please clarify and/or say what error you get / where things go wrong.