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
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
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();
}
}
}
