How to reproduce that error as simply as possible:
Java code:
package javaapplication3;
public class JavaApplication3 {
public static void main(String[] args) {
}
}
class Cat implements Animal{
}
interface Animal{
abstract boolean roar();
}
Shows this compile time error:
Cat is not abstract and does not override abstract method roar() in Animal
Why won’t it compile?
Because:
- You created a class Cat which implements an interface Animal.
- Your interface called Animal has an abstract method called roar which must be overridden.
- You didn’t provide for method roar. There are many ways to eliminate the compile time error.
Remedy 1, have Cat override the abstract method roar()
package javaapplication3;
public class JavaApplication3 {
public static void main(String[] args) {
Cat c = new Cat();
System.out.println(c.roar());
}
}
class Cat implements Animal{
public boolean roar(){
return true;
}
}
interface Animal{
abstract boolean roar();
}
Remedy 2, change Cat to be an abstract like this:
package javaapplication3;
public class JavaApplication3 {
public static void main(String[] args) {
Cat c;
}
}
abstract class Cat implements Animal{
}
interface Animal{
abstract boolean roar();
}
Which means you can’t instantiate Cat anymore.
Remedy 3, have cat stop implementing Animal
package javaapplication3;
public class JavaApplication3 {
public static void main(String[] args) {
Cat c = new Cat();
}
}
class Cat{
}
interface Animal{
abstract boolean roar();
}
Which makes roar() no longer a contract for things that animals must know how to do.
Remedy 3, extend a class rather than implementing an interface
package javaapplication3;
public class JavaApplication3 {
public static void main(String[] args) {
Cat c = new Cat();
System.out.println(c.roar());
}
}
class Cat extends Animal{
}
class Animal{
boolean roar(){
return true;
}
}
The remedy to use depends on what the best model is to represent the problem being represented. The error is there to urge you stop “programming by brownian motion”.
