java-quiz.md

Java

Q1. Given the string "strawberries" saved in a variable called fruit, what would fruit.substring(2, 5) return?

• rawb
• raw
• awb
• traw

Reasoning: The substring method is accepting two arguments. The first argument being the index to start(includes that char at 2) and the second the index of the string to end the substring(excludes the char at 5). Strings in Java are like arrays of chars. Therefore the method will return "raw" as those are the chars in indexes 2,3, and 4. You can also take the ending index and subtract the beginning index from it, to determine how many chars will be included in the substring (5-2=3).

Q2. How can you achieve runtime polymorphism in Java?

• method overloading
• method overrunning
• method overriding
• method calling

Q3. Given the following definitions, which of these expression will NOT evaluate to true?

boolean b1 = true, b2 = false; int i1 = 1, i2 = 2;

• (i1 | i2) == 3
• i2 && b1
• b1 || !b2
• (i1 ^ i2) < 4

Q4. What can you use to create new instances in Java?

• constructor
• another instance
• field
• private method

Q5. What is the output of this code?

1: class Main {
2:   public static void main (String[] args) {
3:     int array[] = {1, 2, 3, 4};
4:     for (int i = 0; i < array.size(); i++) {
5:        System.out.print(array[i]);
6:     }
7:   }
8: }

• It will not compile because of line 4.
• It will not compile because of line 3.
• 123
• 1234

Q6. Which of the following can replace the CODE SNIPPET to make the code below print "Hello World"?

interface Interface1 {
    static void print() {
        System.out.print("Hello");
    }
}

interface Interface2 {
    static void print() {
        System.out.print("World!");
    }
}

• super1.print(); super2.print();
• this.print();
• super.print();
• Interface1.print(); Interface2.print();

Q7. What does the following code print?

String str = "abcde";
str.trim();
str.toUpperCase();
str.substring(3, 4);
System.out.println(str);

• CD
• CDE
• D
• "abcde"

Q8. What is the result of this code?

class Main {
    public static void main (String[] args){
        System.out.println(print(1));
    }
    static Exception print(int i){
        if (i>0) {
            return new Exception();
        } else {
            throw new RuntimeException();
        }
    }
}

• It will show a stack trace with a runtime exception.
• "java.lang.Exception"
• It will run and throw an exception.
• It will not compile.

Q9. Which class can compile given these declarations?

interface One {
    default void method() {
        System.out.println(""One"");
    }
}

interface Two {
    default void method () {
        System.out.println(""One"");
    }
}

• A

class Three implements One, Two {
    public void method() {
        super.One.method();
    }
}

• B

class Three implements One, Two {
    public void method() {
        One.method();
    }
}

• C

class Three implements One, Two {
}

• D

class Three implements One, Two {
    public void method() {
        One.super.method();
    }
}

Q10. What is the output of this code?

class Main {
    public static void main (String[] args) {
        List list = new ArrayList();
        list.add("hello");
        list.add(2);
        System.out.print(list.get(0) instanceof Object);
        System.out.print(list.get(1) instanceof Integer);
    }
}

• The code does not compile.
• truefalse
• truetrue
• falsetrue

Q11. Given the following two classes, what will be the output of the Main class?

package mypackage;
public class Math {
    public static int abs(int num){
        return num < 0 ? -num : num;
    }
}
package mypackage.elementary;
public class Math {
    public static int abs (int num) {
        return -num;
    }
}

import mypackage.Math;
import mypackage.elementary.*;

class Main {
    public static void main (String args[]){
        System.out.println(Math.abs(123));
    }
}

• Lines 1 and 2 generate compiler errors due to class name conflicts.
• "-123"
• It will throw an exception on line 5.
• "123"

Explanation: The answer is "123". The abs() method evaluates to the one inside mypackage.Math class.

Q12. What is the result of this code?

1: class MainClass {
2:  final String message(){
3:      return "Hello!";
4:  }
5: }

6: class Main extends MainClass {
7:  public static void main(String[] args) {
8:      System.out.println(message());
9:  }

10: String message(){
11:     return "World!";
12:  }
13: }

• It will not compile because of line 10.
• "Hello!"
• It will not compile because of line 2.
• "World!"

Explanation: Non-static method message() cannot be referenced from a static context.

Q13. Given this code, which command will output "2"?

class Main {
    public static void main(String[] args) {
        System.out.println(args[2]);
    }
}

• java Main 1 2 "3 4" 5
• java Main 1 "2" "2" 5
• java Main.class 1 "2" 2 5
• java Main 1 "2" "3 4" 5

Q14. What is the output of this code?

class Main {
    public static void main(String[] args){
        int a = 123451234512345;
        System.out.println(a);
    }
}

• "123451234512345"
• Nothing - this will not compile.
• a negative integer value
• "12345100000"

Reasoning: The int type in Java can be used to represent any whole number from -2147483648 to 2147483647. Therefore this code will not compile as the number assigned to 'a' is larger than the int type can hold.

Q15. What is the output of this code?

class Main {
    public static void main (String[] args) {
        String message = "Hello world!";
        String newMessage = message.substring(6, 12)
            + message.substring(12, 6);
        System.out.println(newMessage);
    }
}

• The code does not compile.
• A runtime exception is thrown.
• "world!!world"
• "world!world!"

String m = "Hello world!";
String n = m.substring(6,12) + m.substring(12,6);
System.out.println(n);

Q16. How do you write a foreach loop that will iterate over ArrayList<Pencil>pencilCase?

• for (Pencil pencil : pencilCase) {}
• for (pencilCase.next()) {}
• for (Pencil pencil : pencilCase.iterator()) {}
• for (pencil in pencilCase) {}

Q17. Fill in the blanks?

• Object-oriented programming (OOP) is a programming language model that organizes software design around (objects), rather than (actions).

Q18. What code would you use to tell if "schwifty" is of type String?

• "schwifty".getType() == String
• "schwifty".getClass().getSimpleName() == "String"
• "schwifty".getType().equals("String")
• "schwifty" instanceof String

Q19. What does this code print?

System.out.print("apple".compareTo("banana"));

• 0
• positive number
• negative number
• compilation error

Q20. You have an ArrayList of names that you want to sort alphabetically. Which approach would NOT work?

• names.sort(Comparator.comparing(String::toString))
• Collections.sort(names)
• names.sort(List.DESCENDING)
• names.stream().sorted((s1, s2) -> s1.compareTo(s2)).collect(Collectors.toList())

Q21. By implementing encapsulation, you cannot directly access the class's ___ properties unless you are writing code inside the class itself.

• private
• protected
• no-modifier
• public

Q22. Which is the most up-to-date way to instantiate the current date?

• new SimpleDateFormat("yyyy-MM-dd").format(new Date())
• new Date(System.currentTimeMillis())
• LocalDate.now()
• Calendar.getInstance().getTime()

Explanation: LocalDate is newest class added in java 8

Q23. Fill in the blank to create a piece of code that will tell wether int0 is divisible by 5:

boolean isDivisibleBy5 = _____

• int0 / 5 ? true: false
• int0 % 5 == 0
• int0 % 5 != 5
• Math.isDivisible(int0, 5)

Q24. How many times will this code print "Hello World!"?

class Main {
    public static void main(String[] args){
        for (int i=0; i<10; i=i++){
            i+=1;
            System.out.println("Hello World!");
        }
    }
}

• 10 times
• 9 times
• 5 times
• infinite number of times

Reason : Observe the loop increment. It's not an increment, it's an assignment(post).

Q25. The runtime system starts your program by calling which function first?

• print
• iterative
• hello
• main

Q26. What is the result of this code?

try{
    System.out.print("Hello World");
}catch(Exception e){
    System.out.println("e");
}catch(ArithmeticException e){
    System.out.println("e");
}finally{
    System.out.println("!")
}

• It will throw a runtime exception
• It will not compile
• Hello World!
• Hello World

Q27. Which statement is NOT true?

• An anonymous class may specify an abstract base class as its base type.
• An anonymous class does not require a zero-argument constructor.
• An anonymous class may specify an interface as its base type.
• An anonymous class may specify both an abstract class and interface as base types.

Q28. What will this program print out to the console when executed?

import java.util.LinkedList;

public class Main {
    public static void main(String[] args){
        LinkedList<Integer> list = new LinkedList<>();
        list.add(5);
        list.add(1);
        list.add(10);
        System.out.println(list);
    }
}

• [5, 1, 10]
• [10, 5, 1]
• [1, 5, 10]
• [10, 1, 5]

Q29. What is the output of this code?

class Main {
    public static void main(String[] args){
       String message = "Hello";
       for (int i = 0; i<message.length(); i++){
          System.out.print(message.charAt(i+1));
       }
    }
}

• "Hello"
• A runtime exception is thrown.
• The code does not compile.
• "ello"

Q30. Object-oriented programming is a style of programming where you organize your program around __ rather than __ and data rather than logic.

• functions; actions
• objects; actions
• actions; functions
• actions; objects

Q31. What statement returns true if "nifty" is of type String?

• "nifty".getType().equals("String")
• "nifty".getType() == String
• "nifty".getClass().getSimpleName() == "String"
• "nifty" instanceof String

Q32. What is the output of this code?

import java.util.*;
class Main {
	public static void main(String[] args) {
		List<Boolean> list = new ArrayList<>();
		list.add(true);
		list.add(Boolean.parseBoolean("FalSe"));
		list.add(Boolean.TRUE);
		System.out.print(list.size());
		System.out.print(list.get(1) instanceof Boolean);
	}
}

• A runtime exception is thrown.
• 3false
• 2true
• 3true

Q33. What is the result of this code?

1: class Main {
2: 		Object message(){
3: 			return "Hello!";
4: 		}
5: 		public static void main(String[] args) {
6: 			System.out.print(new Main().message());
7: 			System.out.print(new Main2().message());
8: 		}
9: }
10: class Main2 extends Main {
11: 	String message(){
12: 		return "World!";
13: 	}
14: }

• It will not compile because of line 7.
• Hello!Hello!
• Hello!World!
• It will not compile because of line 11.

Q34. What method can be used to create a new instance of an object?

• another instance
• field
• constructor
• private method

Q35. Which is the most reliable expression for testing whether the values of two string variables are the same?

• string1 == string2
• string1 = string2
• string1.matches(string2)
• string1.equals(string2)

Q36. Which letters will print when this code is run?

public static void main(String[] args) {
	try {
		System.out.println("A");
		badMethod();
		System.out.println("B");
	} catch (Exception ex) {
		System.out.println("C");
	} finally {
		System.out.println("D");
	}
}
public static void badMethod() {
	throw new Error();
}

• A, B, and D
• A, C, and D
• C and D
• A and D

Q37. What is the output of this code?

class Main {
	static int count = 0;
	public static void main(String[] args) {
		if (count < 3) {
			count++;
			main(null);
		} else {
			return;
		}
		System.out.println("Hello World!");
	}
}

• It will throw a runtime exception.
• It will not compile.
• It will print "Hello World!" three times.
• It will run forever.

Q38. What is the output of this code?

import java.util.*;
class Main {
	public static void main(String[] args) {
		String[] array = {"abc", "2", "10", "0"};
		List<String> list = Arrays.asList(array);
		Collections.sort(list);
		System.out.println(Arrays.toString(array));
	}
}

• [abc, 0, 2, 10]
• The code does not compile.
• [abc, 2, 10, 0]
• [0, 10, 2, abc]

Q39. What is the output of this code?

class Main {
	public static void main(String[] args) {
		String message = "Hello";
		print(message);
		message += "World!";
		print(message);
	}
	static void print(String message){
		System.out.print(message);
		message += " ";
	}
}

• Hello World!
• HelloHelloWorld!
• Hello Hello World!
• Hello HelloWorld!

Q40. What is displayed when this code is compiled and executed?

public class Main {
	public static void main(String[] args) {
		int x = 5;
		x = 10;
		System.out.println(x);
	}
}

• x
• null
• 10
• 5

Q41. Which approach cannot be used to iterate over a List named theList?

• A

for (int i = 0; i < theList.size(); i++) {
    System.out.println(theList.get(i));
}

• B

for (Object object : theList) {
    System.out.println(object);
}

• C

Iterator it = theList.iterator();
for (it.hasNext()) {
    System.out.println(it.next());
}

• D

theList.forEach(System.out::println);

Explanation: for (it.hasNext()) should be while (it.hasNext()).

Q42. What method signature will work with this code?

boolean healthyOrNot = isHealthy("avocado");

• public void isHealthy(String avocado)
• boolean isHealthy(String string)
• public isHealthy("avocado")
• private String isHealthy(String food)

Q43. Which are valid keywords in a Java module descriptor (module-infoJava)?

• provides, employs
• imports, exports
• consumes, supplies
• requires, exports

Q44. Which type of variable keeps a constant value once it is assigned?

• non-static
• static
• final
• private

Q45. How does the keyword _volatile_ affect how a variable is handled?

• It will be read by only one thread at a time.
• It will be stored on the hard drive.
• It will never be cached by the CPU.
• It will be preferentially garbage collected.

Q46. What is the result of this code?

char smooch = 'x';
System.out.println((int) smooch);

• an alphanumeric character
• a negative number
• a positive number
• a ClassCastException

Q47. You get a NullPointerException. What is the most likely cause?

• A file that needs to be opened cannot be found.
• A network connection has been lost in the middle of communications.
• Your code has used up all available memory.
• The object you are using has not been instantiated.

Q48. How would you fix this code so that it compiles?

public class Nosey {
	int age;
	public static void main(String[] args) {
		System.out.println("Your age is: " + age);
	}
}

• Make age static.
• Make age global.
• Make age public.
• Initialize age to a number.

Q49. Add a Duck called "Waddles" to the ArrayList ducks.

public class Duck {
	private String name;
	Duck(String name) {}
}

• Duck waddles = new Duck(); ducks.add(waddles);
• Duck duck = new Duck("Waddles"); ducks.add(waddles);
• ducks.add(new Duck("Waddles"));
• ducks.add(new Waddles());

Q50. If you encounter UnsupportedClassVersionError it means the code was ___ on a newer version of Java than the JRE ___ it.

• executed; interpreting
• executed; compiling
• compiled; executing
• compiled, translating

Q51. Given this class, how would you make the code compile?

public class TheClass {
    private final int x;
}

• A

public TheClass() {
    x += 77;
}

• B

public TheClass() {
    x = null;
}

• C

public TheClass() {
    x = 77;
}

• D

private void setX(int x) {
    this.x = x;
}
public TheClass() {
    setX(77);
}

Q52. How many times f will be printed?

public class Solution {
    public static void main(String[] args) {
        for (int i = 44; i > 40; i--) {
            System.out.println("f");
        }
    }
}

• 4
• 3
• 5
• A Runtime exception will be thrown

Q53. Which statements about abstract classes are true?

1. They can be instantiated.
2. They allow member variables and methods to be inherited by subclasses.
3. They can contain constructors.

• 1, 2, and 3
• only 3
• 2 and 3
• only 2

Q54. Which keyword lets you call the constructor of a parent class?

• parent
• super
• this
• new

Q55. What is the result of this code?

  1: int a = 1;
  2: int b = 0;
  3: int c = a/b;
  4: System.out.println(c);

• It will throw an ArithmeticException.
• It will run and output 0.
• It will not compile because of line 3.
• It will run and output infinity.

Q56. Normally, to access a static member of a class such as Math.PI, you would need to specify the class "Math". What would be the best way to allow you to use simply "PI" in your code?

• Add a static import.
• Declare local copies of the constant in your code.
• This cannot be done. You must always qualify references to static members with the class form which they came from.
• Put the static members in an interface and inherit from that interface.

Q57. Which keyword lets you use an interface?

• extends
• implements
• inherits
• import

Q58. Why are ArrayLists better than arrays?

• You don't have to decide the size of an ArrayList when you first make it.
• You can put more items into an ArrayList than into an array.
• ArrayLists can hold more kinds of objects than arrays.
• You don't have to decide the type of an ArrayList when you first make it.

Q59. Declare a variable that holds the first four digits of Π

• int pi = 3.141;
• decimal pi = 3.141;
• double pi = 3.141;
• float pi = 3.141;

Reasoning:

public class TestReal {
    public static void main (String[] argv)
    {
      double pi = 3.14159265;       //accuaracy upto 15 digits
      float pi2 = 3.141F;                //accuracy upto 6-7 digits

      System.out.println ("Pi=" + pi);
      System.out.println ("Pi2" + pi2;
    }
  }

The default Java type which Java will be using for a float variable will be double.
So, even if you declare any variable as float, what the compiler has to actually do is to assign a double value to a float variable,
which is not possible. So, to tell the compiler to treat this value as a float, that 'F' is used.

Q60. Use the magic power to cast a spell

public class MagicPower {
    void castSpell(String spell) {}
}

• new MagicPower().castSpell("expecto patronum")
• MagicPower magicPower = new MagicPower(); magicPower.castSpell();
• MagicPower.castSpell("expelliarmus");
• new MagicPower.castSpell();

Q61. What language construct serves as a blueprint containing an object's properties and functionality?

• constructor
• instance
• class
• method

Q62. What does this code print?

public static void main(String[] args) {
    int x=5,y=10;
    swapsies(x,y);
    System.out.println(x+" "+y);
}

static void swapsies(int a, int b) {
    int temp=a;
    a=b;
    b=temp;
}

• 10 10
• 5 10
• 10 5
• 5 5

Q63. What is the result of this code?

try {
    System.out.println("Hello World");
} catch (Exception e) {
    System.out.println("e");
} catch (ArithmeticException e) {
    System.out.println("e");
} finally {
    System.out.println("!");
}

• Hello World
• It will not compile because the second catch statement is unreachable
• Hello World!
• It will throw runtime exception

Q64. What is not a java keyword

• finally
• native
• interface
• unsigned

Q65. Which operator would you use to find the remainder after division?

• %
• //
• /
• DIV

Reference

Q66. Which choice is a disadvantage of inheritance?

• Overridden methods of the parent class cannot be reused.
• Responsibilities are not evenly distributed between parent and child classes.
• Classes related by inheritance are tightly coupled to each other.
• The internal state of the parent class is accessible to its children.

Reference

Q67. Declare and initialize an array of 10 ints.

• Array<Integer> numbers = new Array<Integer>(10);
• Array[int] numbers = new Array[int](10);
• int[] numbers = new int[10];
• int numbers[] = int[10];

Q68. Refactor this event handler to a lambda expression:

groucyButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("Press me one more time..");
    }
});

• groucyButton.addActionListener(ActionListener listener -> System.out.println("Press me one more time..."));
• groucyButton.addActionListener((event) -> System.out.println("Press me one more time..."));
• groucyButton.addActionListener(new ActionListener(ActionEvent e) {() -> System.out.println("Press me one more time...");});
• groucyButton.addActionListener(() -> System.out.println("Press me one more time..."));

Reference

Q69. Which functional interfaces does Java provide to serve as data types for lambda expressions?

• Observer, Observable
• Collector, Builder
• Filter, Map, Reduce
• Consumer, Predicate, Supplier

Reference

Q69. What is a valid use of the hashCode() method?

• encrypting user passwords
• deciding if two instances of a class are equal
• enabling HashMap to find matches faster
• moving objects from a List to a HashMap

Reference

Q70. What kind of relationship does "extends" denote?

• uses-a
• is-a
• has-a
• was-a

Reference

Q71. How do you force an object to be garbage collected?

• Set object to null and call Runtime.gc()
• Set object to null and call System.gc()
• Set object to null and call Runtime.getRuntime().runFinalization()
• There is no way to force an object to be garbage collected Reference

Q72. Java programmers commonly use design patterns. Some examples are the __, which helps create instances of a class, the __, which ensures that only one instance of a class can be created; and the __, which allows for a group of algorithms to be interchangeable.

• static factory method; singleton; strategy pattern
• strategy pattern; static factory method; singleton
• creation pattern; singleton; prototype pattern
• singleton; strategy pattern; static factory method

Q73. Using Java's Reflection API, you can use __ to get the name of a class and __ to retrieve an array of its methods.

• this.getClass().getSimpleName(); this.getClass().getDeclaredMethods()
• this.getName(); this.getMethods()
• Reflection.getName(this); Reflection.getMethods(this)
• Reflection.getClass(this).getName(); Reflection.getClass(this).getMethods()

Q74. What is a valid use of the hashCode() method?

• moving objects from a List to a HashMap
• deciding if two instances of a class are equal
• enabling HashMap to find matches faster
• encrypting user passwords

Q75. Which access modifier makes variables and methods visible only in the class where they are declared?

• public
• protected
• nonmodifier
• private

Q76. What type of variable can be assigned to only once?

• private
• non-static
• final
• static

Q77. How would you convert a String to an Int?

• "21".intValue()
• String.toInt("21")
• Integer.parseInt("21")
• String.valueOf("21")

Q78. What method should be added to the Duck class to print the name Moby?

public class Duck {
    private String name;

    Duck(String name) {
        this.name = name;
    }

    public static void main(String[] args) {
        System.out.println(new Duck("Moby"));
    }
}

• public String toString() { return name; }
• public void println() { System.out.println(name); }
• String toString() { return this.name; }
• public void toString() { System.out.println(this.name); }

Q79. Which operator is used to concatenate Strings in Java

• -
• &
• .
• -

Q80. How many times does this loop print "exterminate"?

for (int i = 44; i > 40; i--) {
    System.out.println("exterminate");
}

• two
• four
• three
• five

Q81. What is the value of myCharacter after line 3 is run?

1: public class Main {
2:   public static void main (String[] args) {
3:     char myCharacter = "piper".charAt(3);
4:   }
5: }

• p
• r
• e
• i

Q82. When should you use a static method?

• when your method is related to the object's characteristics
• when you want your method to be available independently of class instances
• when your method uses an object's instance variable
• when your method is dependent on the specific instance that calls it

Q83. What phrase indicates that a function receives a copy of each argument passed to it rather than a reference to the objects themselves?

• pass by reference
• pass by occurrence
• pass by value
• API call

Q84. In Java, what is the scope of a method's argument or parameter?

• inside the method
• both inside and outside the method
• neither inside nor outside the method
• outside the method

Q85. What is the output of this code?

public class Main {
  public static void main (String[] args) {
    int[] sampleNumbers = {8, 5, 3, 1};
    System.out.println(sampleNumbers[2]);
  }
}

• 5
• 8
• 1
• 3

Q86. Which change will make this code compile successfully?

1: public class Main {
2:   String MESSAGE ="Hello!";
3:   static void print(){
4:     System.out.println(message);
5:   }
6:   void print2(){}
7: }

• Change line 2 to public static final String message
• Change line 6 to public void print2(){}
• Remove the body of the print2 method and add a semicolon.
• Remove the body of the print method.

Q87. What is the output of this code?

import java.util.*;
class Main {
  public static void main(String[] args) {
    String[] array = new String[]{"A", "B", "C"};
    List<String> list1 = Arrays.asList(array);
    List<String> list2 = new ArrayList<>(Arrays.asList(array));
    List<String> list3 = new ArrayList<>(Arrays.asList("A", new String("B"), "C"));
    System.out.print(list1.equals(list2));
    System.out.print(list1.equals(list3));
  }
}

• falsefalse
• truetrue
• falsetrue
• truefalse

Q88. Which code snippet is valid?

• ArrayList<String> words = new ArrayList<String>(){"Hello", "World"};
• ArrayList words = Arrays.asList("Hello", "World");
• ArrayList<String> words = {"Hello", "World"};
• ArrayList<String> words = new ArrayList<>(Arrays.asList("Hello", "World"));

Q89. What is the output of this code?

class Main {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("hello");
    sb.deleteCharAt(0).insert(0, "H")." World!";
    System.out.println(sb);
  }
}

• A runtime exception is thrown.
• "HelloWorld!"
• "hello"
• ????

90. What code would you use in Constructor A to call Constructor B?

public class Jedi {
  /* Constructor A */
  Jedi(String name, String species){}
  
  /* Constructor B */
  Jedi(String name, String species, boolean followsTheDarkSide){}
  }

• Jedi(name, species, false)
• new Jedi(name, species, false)
• this(name, species, false)
• super(name, species, false)

Q91. Which is not a valid lambda expression?

• a -> false;
• (a) -> false;
• String a -> false;
• (String a) -> false;

Q92. By implementing encapsulation, you cannot directly access the class's ______ properties unless you are writing code inside the class itself.

• private
• package-private (no explicit modifier)
• public
• protected