== Why is this an issue?

The purpose of an abstract class is to provide some heritable behaviors while also defining methods which must be implemented by sub-classes.


A class with no abstract methods that was made abstract purely to prevent instantiation should be converted to a concrete class (i.e. remove the ``++abstract++`` keyword) with a private constructor.


A class with only abstract methods and no inheritable behavior should be converted to an interface.


=== Noncompliant code example

[source,text]
----
public abstract class Animal {  // Noncompliant; should be an interface
  abstract void move();
  abstract void feed();
}

public abstract class Color {  // Noncompliant; should be concrete with a private constructor
  private int red = 0;
  private int green = 0;
  private int blue = 0;

  public int getRed() {
    return red;
  }
}
----


=== Compliant solution

[source,text]
----
public interface Animal {
  void move();
  void feed();
}

public class Color {
  private int red = 0;
  private int green = 0;
  private int blue = 0;

  private Color () {}

  public int getRed() {
    return red;
  }
}

public abstract class Lamp {

  private boolean switchLamp=false;

  public abstract void glow();

  public void flipSwitch() {
    switchLamp = !switchLamp;
    if (switchLamp) {
      glow();
    }
  }
}
----