I get this error:

incompatible types
found : double
required: java.lang.String
zwembad = Lengte + Breedte + Diepte;


Can anyone tell me what this means?

i have checked my code several times.



This is my code if you are interrested:

// Its a swimming pool that uses length, width and depth.
content is calculated with: length, width and depth


import java.lang.String;

public class Zwembad
{
double Lengte;
double Breedte;
double Diepte;
double Inhoud;


//Methode
public Zwembad(double zbLengte, double zbBreedte, double zbDiepte)
{
Lengte = zbLengte;
Breedte = zbBreedte;
Diepte = zbDiepte;

}
//Methode

public double setLengte ()
{
return Lengte;
}

public double setBreedte ()
{
return Breedte;
}

public double setDiepte ()
{
return Diepte;
}

public double getinhoud ()
{
return (Lengte + Breedte + Diepte);
}

public String toString()
{
String zwembad;
zwembad = Lengte + Breedte + Diepte;
return zwembad;
}
}


this is the main file thats uses "zwembad"


public class Main {

public static void main (String [ ] argv)
{
Zwembad z = new Zwembad (2.0, 5.5, 1.5);
System.out.println (z.getInhoud());
}
}