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 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

Q5. 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();

Q6. 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"

Q7. 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.

Q8. 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();
    }
}

Q9. 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

Q10. 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, because The import statements of the form:

import packageName.subPackage.*

is Type-Import-on-Demand Declarations, which never causes any other declaration to be shadowed.

Q11. 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: Compilation error at line 10 because of final methods cannot be overridden, and here message() is a final method, and also note that Non-static method message() cannot be referenced from a static context.

Q12. 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

Q13. 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.

Q14. 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!"

Q15. 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) {}

Q16. What does this code print?

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

0
positive number
negative number
compilation error

Q17. 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())

Q18. 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

Q19. 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 the newest class added in java 8

Q20. Fill in the blank to create a piece of code that will tell whether `int0` is divisible by `5`:

boolean isDivisibleBy5 = _____

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

Q21. 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

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

Q22. The runtime system starts your program by calling which function first?

print
iterative
hello
main

Q23. 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)

Note: This code won't compile, possibly broken code sample.

Q24. 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.

Q25. 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]

Q26. 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"

Q27. 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

Q28. What statement returns true if "nifty" is of type String?

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

Q29. 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

Q30. 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.

Q31. What method can be used to create a new instance of an object?

another instance
field
constructor
private method

Q32. 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)

Q33. 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

Explanation: Error is not inherited from Exception

Q34. 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.

Q35. 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]

Explanation: The java.util.Arrays.asList(T... a) returns a fixed-size list backed by the specified array. (Changes to the returned list "write through" to the array.)

Q36. 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!

Q37. 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

Q38. 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()).

Q39. 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)

Q40. Which are valid keywords in a Java module descriptor (module-info.java)?

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

Q41. Which type of variable keeps a constant value once it is assigned?

non-static
static
final
private

Q42. 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.

Q43. 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

Q44. 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.

Q45. 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.

Q46. 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());

Q47. 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

Q48. 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);
}

Explanation: final class members are allowed to be assigned only in three places: declaration, constructor or an instance-initializer block.

Q49. 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

Q50. 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

Q51. Which keyword lets you call the constructor of a parent class?

parent
super
this
new

Q52. 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.

Q53. 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.

Q54. Which keyword lets you use an interface?

extends
implements
inherits
import

Q55. 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.

Q56. 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;       //accuracy up to 15 digits
      float pi2 = 3.141F;           //accuracy up to 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.

Q57. 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();

Q58. What language construct serves as a blueprint containing an object's properties and functionality?

constructor
instance
class
method

Q59. 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

Q60. 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

Q61. Which is not a java keyword

finally
native
interface
unsigned

Explanation: native is a part of JNI interface

Q62. Which operator would you use to find the remainder after division?

%
//
/
DIV

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