Chapter 2 - Review Questions Attemp 5

Results:

Date: 15/01/2024
Score: 17/20 (85)

Question #	Correct
1	✅
2	✅
3	✅
4	❌
5	✅
6	✅
7	✅
8	❌
9	✅
10	✅
11	✅
12	✅
13	❌
14	✅
15	✅
16	✅
17	✅
18	✅
19	✅
20	✅

🟧 Question 1

❓Which of the following statements about design principles and design patterns are true (choose all which apply)❓

A. A design principle is focused on solving a specific commonly occuring problem
B. Design principles and design patterns are the same thing
C. Design principles are often applied throught an application, whereas design patterns are applied to solve specific problems
D. Design patterns can only be applied to static classes
E. Design principles and design patterns tend to produce code that is easier to maintain and easier for other developers to read

My Answer:

• A - false, design principles are ideas which can be applied generally
• B - false
• C - true
• D - false
• E - true
• C,E✅✅✅✅

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🟧 Question 2

❓What is the result of the following code❓

1: public interface CanClimb {
2:     public abstract void climb();
3: }
4: public interface CanClimbTrees extends CanClimb {}
5: public abstract class Chipmunk implements CanClimbTrees {
6:     public abstract void chew();
7: }
8: public class EasternChipmunk extends Chipmunk {
9:     public void chew() { System.out.println("Eastern  Chipmunk is Chewing";}
10: }

A. It compiles and runs without issue
B. The code will not compile because of line 2
C. The code will not compile because of line 4
D. The code will not compile because of line 5
E. The code will not compile because of line 8
F. It compiles but throws exception at runtime

My Answer:

• Chipmunk has climb and chew as abstract methods
• Therefore line 8 will not compile
• E✅✅✅✅

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🟧 Question 3

❓Which of the following are functional interrfaces❓

public interface Climb {
    public int climb();
}
public abstract class Swim {
    public abstract Object swim(double speed, int duration);
}
public interface ArcticMountainClimb extends MountainClimb {
    public default int getSpeed();
}
public interface MountainClimb extends Climb {}

A. Climb
B. Swim
C. ArcticMountainClimb
D. MountainClimb
E. None of these are valid functional interfaces

My Answer:

• Climb, and MountainClimb are functional interfaces
• Swim is an abstract class!
• A,D✅✅✅✅

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🟧 Question 4

❓Which of the following are valid lambda expressions (choose all that apply)❓

A. () -> ""
B. x,y -> x+y
C. (Coyote y) -> return 0; <br> D. (Camel c) -> {return; }
E. Wolf w -> 39
F. () ->
G. (Animal z, m)-> a

My Answer:

• A - valid
• B - invalid, needs round brackets
• C - valid
• D - valid
• E - invalid, needs round brackets
• F - invalid, m must have a type
• A,C,D❌❌❌❌
• CORRECT ANSWER: A,D

• C needs curly braces!

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🟧 Question 5

❓What are some of the properties of the singleton pattern (choose all that apply)❓

A. Singleton object can be replaced with encapsulated setter method
B. Requires contructor of singleton class to be private
C. Singleton object must be named instance
D. Single object may be private or protected
E. Ensure that there is only one instance of an object in memory
F. Required a public static method to retrieve the instance of the singleton

My Answer:

• Singleton ensures that there is only a single instance in memory
• A - false
• B - true
• C - false
• D - false, must be private
• E - true
• F - true
• B,E,F✅✅✅✅

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🟧 Question 6

❓What is the result of the following class❓

import java.util.function.*;
public class Panda {
    int age;
    public static void main(String[] args) {
        Panda p1 = new Panda();
        p1.age = 1;
        check(p1, p -> p.age < 5); // h1
    }
    private static void check(Panda panda, Predicate<Panda> pred) { // h2
        String result = pred.test(panda) ? "match" : "not match"; // h3
        System.out.println(result);
    }
}

A.  `match`🎃
B.  `not match`🎃
C.  `Compiler error on line h1`🎃
D.  `Compiler error on line h2`🎃
E.  `Compiler error on line h3`🎃
F.  `A runtime exception is thrown`🎃

My Answer:

• This code compiles, and prints match
• A✅✅✅✅

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🟧 Question 7

❓What changes need to be made to make the following immutable object pattern correct❓

import java.util.*;
public class Seal {
    String name;
    private final List<Seal> friends;
    public Seal(String name, List<Seal> friends) {
        this.name = name;
        this.friends = friends;
    }
    public String getName() { return name; }
    public List<Seal> getFriends() { return friends; }
}

A. None; the immutable object pattern is properly implemented.
B. Have Seal implement the Immutable interface
C. Mark name final and private
D. Add setters for name and List<Seal> friends
E. Replace the getFriends() method with methods that do not give the caller direct access to the List<Seal> friends
F. Change type of List<Seal> to List<Object>
G. Make a copy of the List<Seal> friends in the constructor
H. Make the Seal class final

My Answer:

• An immutable class is marked final, has private final variables, a public constructor, and no setters
• A - false, the getFriends() returns a direct reference of a mutable object
• B - false, does not exist
• C - true
• D - false
• E - true
• F - false
• G - true, although I incorrectly assumed this was false to begin with
• H - true
• C,E,G,H✅✅✅✅

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🟧 Question 8

❓Which of the following are true of interfaces (choose all that apply)❓

A. They can extend other classes
B. They can not be extended
C. They enable classes to have multiple inheritance
D. They can only contain abstract methods
E. They can be declared final
F. All members of an interface are public

My Answer:

• A - true, they can extend interfaces
• B - false
• C - true
• D - false
• E - false, this will prevent implementation
• F - true
• A,C,F❌❌❌❌
• CORRECT ANSWER: C,F

• While interfaces can extend interfaces, they can not extend regular classes!!!

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🟧 Question 9

❓What changes need to be made to make the following singleton pattern correct?❓

public class CheetahManager {
    public static CheetahManager cheetahManager;
    private CheetahManager() {}
    public static CheetahManager getCheetahManager() {
        if (cheetahManager == null) {
            cheetahManager = new CheetahManager();
        }
        return cheetahManager;
    }
}

A. None; the singleton pattern is properly implemented
B. Rename cheetahManager to instance
C. Rename getCheetahManager() to getInstance()
D. Change the access modifier of cheetahManager from public to private
E. Mark cheetahManager final
F. Add synchronized to getCheetahManager()

My Answer:

• The instance must be private
• The get method must be synchronized
• A - false
• B - false
• C - false
• D - true
• E - false, not necessary
• F - true
• D,F✅✅✅✅

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🟧 Question 10

❓What is the result of the following code?❓

1:  public interface CanWalk {
2:      default void walk() { System.out.println("Walking"); }
3:  }
4:  public interface CanRun {
5:      public default void walk() { System.out.println("Walking"); }
6:      public abstract void run();
7:  }
8:  public interface CanSprint extends CanWalk, CanRun {
9:      void sprint();
10: }

A. The code compiles without issue
B. The code will not compile because of line 5
C. The code will not compile because of line 6
D. The code will not compile because of line 8
E. The code will not compile because of line 9

My Answer:

• The interface can not extend two interfaces with a default method of same signature
• D✅✅✅✅

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🟧 Question 11

❓Which lambda can replace the MySecret class to return the same value (choose all that apply)❓

public interface Secret {
    String magic(double d);
}
public class MySecret implements Secret {
    public String magic(double d) {
        return "Poof";
    }
}

A. caller((e) -> "Poof");
B. caller((e) -> {"Poof"});
C. caller((e) -> { String e = ""; "Poof"; });
D. caller((e) -> { String e = ""; return "Poof"; });
E. caller((e) -> { String e = ""; return "Poof" });
F. caller((e) -> { String f = ""; return "Poof"; });

My Answer:

• A,F✅✅✅✅

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🟧 Question 12

❓What is the result of the following code?❓

public interface Climb {
    boolean isTooHigh(int height, int limit);
}
public class Climber {
    public static void main(String[] args) {
        check((h,l) -> h.toString(), 5); // x1
    }
    private static void check(Climb climb, int height) {
        if (climb.isTooHigh(height, 10)) // x2
            System.out.println("too high");
        else System.out.println("ok");
    }
}

A. ok
B. too high
C. Compiler error on line x1
D. Compiler error on line x2
E. Compiler error on a different line
F. A runtime exception is thrown.

My Answer:

• C✅✅✅✅

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🟧 Question 13

❓ Which of the following are properties of classes that define immutable objects? (Choose all tha apply)❓

A. They don't define any getter methods
B. All of the instance variables marked private and final
C. They don't define any setter methods
D. They mark all instance variables static
E. They prevent methods from being overridden
F. All getter methods are marked synchronized

My Answer:

• Immutable classes have private final fields, and is marked final itself

• A - false, not necessary

• B - true

• C - true

• D - false

• E - false

• F - false

• B,C❌❌❌❌

• CORRECT ANSWER: B,C,E

• Preventing subclasses from overriding method is essential to preserving immutability

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🟧 Question 14

❓Which of the following statements can be inserted in the blank line so that the code will compile successfully? (Choose all that apply)❓

public interface CanHop {}
public class Frog implements CanHop {
    public static void main(String[] args) {
        _________ frog = new TurtleFrog();
    }
}
public class BrazillianHornedFrog extends Frog {}
public class TurtleFrog extends Frog {}

A. Frog
B. TurtleFrog
C. BrazillianHornedFrog
D. CanHop
E. Object
F. Long

My Answer:

• Can have Object, TurtleFrog, Frog, CanHop
• A,B,D,E✅✅✅✅

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🟧 Question 15

❓ Which of the following statements about polymorphism are true? (choose all that apply) ❓

A. A reference to an object may be cast to a subclass of the object without an explicit cast.
B. If a method takes a class that is the superclass of three different object references, then any of those object may be passed as a parameter to the method
C. A reference to an object may be cast to a superclass of the object without an explicit cast.
D. All cast exceptions can be detected at compile time
E. By defining public instance method in the superclass, you guarantee that the specific method will be called in the parent class at runtime

My Answer:

• A - false
• B - true
• C - true
• D - false
• E - false
• B,C✅✅✅✅

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🟧 Question 16

❓Choose the correct statement about the following code:❓

1: public interface Herbivore {
2:     int amount = 10;
3:     public static void eatGrass();
4:     public int chew() {
5:         return 13;
6:     }
7: }

A. It compiles and runs without issue
B. The code will not compile because of line 2
C. The code will not compile because of line 3
D. The code will not compile because of line 4
E. The code will not compile because of line 2 and 3
F. The code will not compile because of line 3 and 4

My Answer:

• F✅✅✅✅

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🟧 Question 17

❓Which of the following are properties of classes that are properly encapsulated as a JavaBean (Choose all that apply)❓

A. All instance variable are marked final
B. boolean instance variables are accessed with is or get
C. All instance variables are marked private
D. They implement the JavaBean interface
E. Variables are created using lazy instantiation
F. The first letter of the any getter/setter, after the get, set, or is prefix, must be upper case

My Answer:

• B,C,F✅✅✅✅

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🟧 Question 18

❓Which of the following statements about inheritance and object composition are correct? (Choose all that apply)❓

A. Inheritance supports access to protected variables
B. Object composition tends to promote greater code reuse than inheritance
C. Inheritance relies on the has-a principle
D. Object composition supports method overriding at runtime
E. Object composition requires a class variable to be public or accessible from a public method to be used by a class in a different package
F. Object composition is always preferred to inheritance.

My Answer:

• A - true
• B - true
• C - false
• D - false, this is inheritance
• E - true
• F - false
• A,B,E✅✅✅✅

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🟧 Question 19

❓Which three scenarios would best benefit from using the singleton pattern (Choose all three)❓

A. Create read-only objects that are thread-safe
B. Manage a reusable cache of objects
C. Ensure that all objects are lazily instantiated
D. Manage write access to a log file
E. Provide central access to application configuration data
F. Allow multiple instances of a static object to be managed in memory

My Answer:

• B,D,E✅✅✅✅

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🟧 Question 20

❓Choose the correct statement about the following code❓

1: public interface CanFly {
2:     void fly();
3: }
4: interface HasWings {
5:     public abstract Object getWingSpan();
6: }
7: abstract class Falcon implements CanFly, HasWings {
8: }

A. It compiles without issue
B. The code will not compile because of line 2
C. The code will not compile because of line 4
D. The code will not compile because of line 5
E. The code will not compile because of line 2 and 5
F. The code will not compile because of class Falcon does not implement the interface methods

My Answer:

• A✅✅✅✅

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