Java Language Interfaces Implementing multiple interfaces
Example
A Java class can implement multiple interfaces.
public interface NoiseMaker {
String noise = "Making Noise"; // interface variables are public static final by default
String makeNoise(); //interface methods are public abstract by default
}
public interface FoodEater {
void eat(Food food);
}
public class Cat implements NoiseMaker, FoodEater {
@Override
public String makeNoise() {
return "meow";
}
@Override
public void eat(Food food) {
System.out.println("meows appreciatively");
}
}
Notice how the Cat class must implement the inherited abstract methods in both the interfaces. Furthermore, notice how a class can practically implement as many interfaces as needed (there is a limit of 65,535 due to JVM Limitation).
NoiseMaker noiseMaker = new Cat(); // Valid
FoodEater foodEater = new Cat(); // Valid
Cat cat = new Cat(); // valid
Cat invalid1 = new NoiseMaker(); // Invalid
Cat invalid2 = new FoodEater(); // Invalid
Note:
- All variables declared in an interface are
public static final - All methods declared in an interface methods are
public abstract(This statement is valid only through Java 7. From Java 8, you are allowed to have methods in an interface, which need not be abstract; such methods are known as default methods) - Interfaces cannot be declared as
final - If more than one interface declares a method that has identical signature, then effectively it is treated as only one method and you cannot distinguish from which interface method is implemented
- A corresponding InterfaceName.class file would be generated for each interface, upon compilation
