In the code below, the method calcArea$()$ is an example of what principle?

class Square

private float side

public setSide$($ float value $)$ returns nothing

this.side $=$ value

public getSide$()$ returns float s

s $=$ this.side

public calcArea$()$ returns float area

area $=$ side $*$ side

endclass

class Rectangle inheritsFrom Square

Declarations

private float longSide

public setLongSide$($ float value $)$ returns nothing

this.longSide $=$ value

public getLongSide$()$ returns float side

side $=$ this.longSide

public calcArea$()$ returns float area

area $=$ this.side $*$ this.longSide

endclass