Mutators

A method that changes the state of an object is called a mutator, or a setter. Often the name of these methods starts with "set".

Often a mutator method checks the suggested change and does not make it if there is a problem. For example, Cones should not have negative values for height and radius. Here is the code, with space for the setHeight() method. (More methods will be added later.)

 
// file: Cone.java
//
public class Cone
{
  private double radius;  // radius of the base
  private double height;  // height of the cone
  
  public Cone( double radius, double height )
  {
    this.radius = radius;
    this.height = height;
  }
  
  public double area()
  {
    return Math.PI*radius*(radius + Math.sqrt(height*height + radius*radius) );
  }
  
  public double volume()
  {
    return Math.PI*radius*radius*height/3.0;
  }
  
   void setHeight(   )
  {
    if (  )
      this.height =  ;
  }
  
}

If the parameter is negative leave the instance variable unchanged. In a small program, or for debugging, it might be OK to write an error message. But in large programs you should avoid too many error messages in too many places.

Answer:

Mutators

QUESTION 21: