The Java Interview Handbook: 300+ Interview Questions/

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Inheritance Gotchas

Inheritance Gotchas

This lesson contains questions on inheritance in Java.

We'll cover the following...
Technical Quiz
1.

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()
A.

“Ola”

B.

“----”

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Java
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;
    }
}
Technical Quiz
1.

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()

A.

will not compile

B.

I am a SUV

C.

I am a vehicle

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Java
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();
    }
}
Technical Quiz
1.

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?

A.

No

B.

Yes

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Java
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.");
    }
}
Technical Quiz
1.

Consider the two classes below:

class Parent {
    public void dummyMethod(){

    }
}

class Child extends Parent {
    protected void dummyMethod(){

    }
}

What is wrong with the above code?

A.

Both the class declarations are missing the access modifiers

B.

The overridden method dummyMethod in the Child class is specified a more restrictive access modifier than in the Parent class.

C.

dummyMethod has no method body

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# Takeaways

  • Instance methods in base classes can be overridden by derived classes.

  • If a ...