Question 1

Which statement is true for the following code?

public class Plant {
   private String name;
   public Plant(String name) { this.name = name; }
   public String getName() { return name; }
}

public class Tree extends Plant {
   public void growFruit() { }
   public void dropLeaves() { }
}

java

The code will compile without changes.
The code will compile if public Tree() { Plant(); } is added to the Tree class.
The code will compile if public Plant() { Tree(); } is added to the Plant class.
The code will compile if public Plant() { this("fern"); } is added to the Plant class.

Answer

Correct Option: D

Question 2

What will the result for following code?

public class Yikes {
    public static void go(Long n) {System.out.println("Long ");}
    public static void go(Short n) {System.out.println("Short ");}
    public static void go(int n) {System.out.println("int ");}

    public static void main(String [] args) {
        short y = 6;
        long z = 7;
        go(y);
        go(z);
    }
}

java

int Long
Short Long
Compilation fails.
An exception is thrown at runtime.

Answer

Correct Option: A

Question 3

Which two statements are true about has-a and is-a relationships?

java

Inheritance represents an is-a relationship.
Inheritance represents a has-a relationship.
Interfaces must be used when creating a has-a relationship.
Instance variables can be used when creating a has-a relationship.

Answer

Correct Option: A,D

Question 4

Which two, independently, will allow Sub to compile?

1. class Super {
2.   private int a;
3.   protected Super(int a) { this.a = a; }
4. }
...
11. class Sub extends Super {
12.   public Sub(int a) { super(a); }
13.   public Sub() { this.a = 5; }
14. }

java

Change line 2 to: public int a;
Change line 2 to :protected int a;
Change line 13 to :public Sub() { this(5); }
Change line 13 to :public Sub() { super(5); }

Answer

Correct Option: C,D

Question 5

What will be the output?

public class Base {
  public static final String FOO = "foo";
  public static void main(String[] args) {
    Base b = new Base();
    Sub s = new Sub();
    System.out.print(Base.FOO);
    System.out.print(Sub.FOO);
    System.out.print(b.FOO);
    System.out.print(s.FOO);
    System.out.print(((Base)s).FOO);
  } 
}

class Sub extends Base {
    public static final String FOO="bar";
}

java

foofoofoofoofoo
foobarfoobarbar
foobarfoofoofoo
foobarfoobarfoo
barbarbarbarbar

Answer

Correct Option: D

Question 6

Which two statements are true?

java

An encapsulated, public class promotes re-use.
Classes that share the same interface are always tightly encapsulated.
An encapsulated class allows subclasses to overload methods, but does NOT allow overriding methods.
An encapsulated class allows a programmer to change an implementation without affecting outside code.

AI Explanation

AI 1

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) An encapsulated, public class promotes re-use - This option is true. Encapsulation refers to the practice of hiding internal implementation details of a class and providing a public interface for interacting with the class. By encapsulating the internal details, the class becomes more modular and can be easily reused in different parts of a program.

Option B) Classes that share the same interface are always tightly encapsulated - This option is incorrect. Two classes that share the same interface may or may not be tightly encapsulated. Encapsulation is about hiding implementation details, while an interface defines a contract for interacting with a class. It is possible for multiple classes to implement the same interface but have different levels of encapsulation.

Option C) An encapsulated class allows subclasses to overload methods, but does NOT allow overriding methods - This option is incorrect. Encapsulation does not restrict the ability to override methods. Overloading refers to defining multiple methods with the same name but different parameters, while overriding refers to redefining a method in a subclass with the same name and parameters as the method in the superclass. Encapsulation is unrelated to these concepts.

Option D) An encapsulated class allows a programmer to change an implementation without affecting outside code - This option is true. Encapsulation allows the internal implementation details of a class to be hidden from outside code. This means that the class can be modified or refactored internally without affecting the code that interacts with the class. As long as the public interface remains the same, the outside code will not be affected.

The correct answers are A) An encapsulated, public class promotes re-use and D) An encapsulated class allows a programmer to change an implementation without affecting outside code. These options are true because encapsulation promotes reusability and allows for changes in implementation without affecting the code that interacts with the class.

Answer

Correct Option: A,D

Question 7

What is the output?

public class Wow {
 public static void go(short n) {System.out.println("short");}
 public static void go(Short n) {System.out.println("SHORT");}
 public static void go(Long n) {System.out.println(" LONG");}
 public static void main(String [] args) {
   Short y = 6;
   int z = 7;
   go(y);
   go(z);
 }
}

java

short LONG
SHORT LONG
Compilation fails.
An exception is thrown at runtime.

Answer

Correct Option: C

Question 8

Which statement is true

public class CreditCard {

 private String cardID;
 private Integer limit;
 public String ownerName;

 public void setCardInformation(String cardID,
 String ownerName,
 Integer limit) {
  this.cardID = cardID;
  this.ownerName = ownerName;
  this.limit = limit;
 }
}

java

The class is fully encapsulated.
The code demonstrates polymorphism.
The ownerName variable breaks encapsulation.
The cardID and limit variables break polymorphism.
The setCardInformation method breaks encapsulation.

Answer

Correct Option: C

Question 9

What is the output?

interface TestA { String toString(); }
 public class Test {
 public static void main(String[] args) {
  System.out.println(new TestA() {
  public String toString() { return "test"; }
 });
 }
}

java

test
null
Compilation fails because of an error in line 1.
An exception is thrown at runtime.

Answer

Correct Option: A

Question 10

Which three methods, inserted individually at line 14, will correctly complete class Two?

class One {
 void foo() { }
}
class Two extends One {
 //insert method here
}

java

int foo() { /* more code here */ }
void foo() { /* more code here */ }
public void foo() { /* more code here */ }
private void foo() { /* more code here */ }
protected void foo() { /* more code here */ }

Answer

Correct Option: B,C,E

Description: Java OOPs Quiz - SCJP
Number of Questions: 10
Created by: Aliensbrain Bot
Tags: java scjp

Java OOPs Quiz - SCJP

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