Inheritance Gotchas
This lesson contains questions on inheritance in Java.
We'll cover the following...
Consider the setup below:
public class Language {
static String lang = "base language";
static protected void printLanguage() {
System.out.println(lang);
}
protected Language sayHello() {
System.out.println("----");
return this;
}
}
public class Spanish extends Language {
static String lang = "Spanish";
static protected void printLanguage() {
System.out.println(lang);
}
protected Language sayHello() {
System.out.println("Ola!");
return this;
}
}
What would be the outcome of the below code snippet?
(new Spanish()).sayHello()
“Ola”
“----”
class Demonstration {public static void main( String args[] ) {(new Spanish()).sayHello();Language lg = new Spanish();lg.sayHello();}}class Language {static String lang = "base language";static protected void printLanguage() {System.out.println(lang);}protected Language sayHello() {System.out.println("----");return this;}}class Spanish extends Language {static String lang = "Spanish";static protected void printLanguage() {System.out.println(lang);}protected Language sayHello() {System.out.println("Ola!");return this;}}
Consider the class setup below:
public interface Vehicle {
default void whatAmI() {
System.out.println("I am a vehicle");
}
}
public interface SevenSeater extends Vehicle {}
public interface SUV extends Vehicle {
default void whatAmI() {
System.out.println("I am a SUV");
}
}
public class TeslaModelX implements SUV, SevenSeater {
public void identifyMyself() {
whatAmI();
}
}
What will be the output of (new TeslaModelX()).identifyMyself()
will not compile
I am a SUV
I am a vehicle
class Demonstration {public static void main( String args[] ) {(new TeslaModelX()).identifyMyself();}}interface Vehicle {default void whatAmI() {System.out.println("I am a vehicle");}}interface SevenSeater extends Vehicle {}interface SUV extends Vehicle {default void whatAmI() {System.out.println("I am a SUV");}}class TeslaModelX implements SUV, SevenSeater {public void identifyMyself() {whatAmI();}}
Consider the class setup below:
public interface SuperPower {
void fly();
}
public class JetPack {
public void fly() {
System.out.println("fly away");
}
}
public class FlyingMan extends JetPack implements SuperPower {
void identify() {
System.out.println("I am a flying man.");
}
}
The class FlyingMan implements the interface SuperPower but doesn’t provide an implementation for it directly. Will this code snippet compile since the class JetPack has a fly method?
No
Yes
class Demonstration {public static void main( String args[] ) {(new FlyingMan()).fly();}}interface SuperPower {void fly();}class JetPack {public void fly() {System.out.println("fly away");}}class FlyingMan extends JetPack implements SuperPower {void identify() {System.out.println("I am a flying man.");}}
Consider the two classes below:
class Parent {
public void dummyMethod(){
}
}
class Child extends Parent {
protected void dummyMethod(){
}
}
What is wrong with the above code?
Both the class declarations are missing the access modifiers
The overridden method dummyMethod in the Child class is specified a more restrictive access modifier than in the Parent class.
dummyMethod has no method body
Instance methods in base classes can be overridden by derived classes.
If a ...