Code Snippets-based MCQs

Loops

Table of contents

1. Easy Level MCQs
2. Slightly harder MCQs
3. Tricky MCQs

Easy Level MCQs

The questions are based on frequently used Java 8 String methods:

1. What will the following code print?

    String text = "Java Programming";
    System.out.println(text.substring(5));
   

   Programming
   Java Programming
   Jav
   Java
   
   Answer

   Programming
   (Explanation: substring(5) starts from index 5, returning the substring starting from ‘P’.)

2. What is the return type of the method toUpperCase() in the following code?

    String str = "hello";
    String result = str.toUpperCase();
   

   String
   char
   boolean
   int
   
   Answer

   String
   (Explanation: toUpperCase() returns a new string where all characters are converted to uppercase.)

3. Which method would you use to check if a string “Java” contains the substring “av”?

    String str = "Java";
   

   str.contains("av")
   str.indexOf("av")
   str.matches("av")
   str.equals("av")
   
   Answer

   str.contains(“av”)
   (Explanation: contains() checks if the substring exists within the string.)

4. What does the following code output?

    String str = "Java Programming";
    System.out.println(str.replace('a', 'o'));
   

   Jovo Progromming
   Jova Progromming
   Javo Progromming
   Jova Programming
   
   Answer

   Jovo Progromming
   (Explanation: replace('a', 'o') replaces all occurrences of ‘a’ with ‘o’.)

5. What is the return value of str.trim() when the string is “ Hello “?

    String str = "   Hello   ";
    System.out.println(str.trim());
   

   "Hello"
   " Hello"
   "Hello "
   " Hello "
   
   Answer

   “Hello”
   (Explanation: trim() removes leading and trailing whitespace from the string.)

6. What will the following code output?

    String str = "Java";
    System.out.println(str.charAt(2));
   

   J
   a
   v
   r
   
   Answer

   v
   (Explanation: charAt(2) returns the character at index 2, which is ‘v’.)

7. Which method should you use to split a string “Java Programming” into words?

    String str = "Java Programming";
   

   str.split(" ")
   str.split("")
   str.split(",")
   str.split("/")
   
   Answer

   str.split(“ “)
   (Explanation: split(" ") splits the string at spaces, resulting in words.)

8. What is the return type of the toLowerCase() method?

    String str = "HELLO";
    String result = str.toLowerCase();
   

   String
   char
   boolean
   int
   
   Answer

   String
   (Explanation: toLowerCase() returns a new string where all characters are converted to lowercase.)

9. What is the output of the following code?

    String str = "Java";
    System.out.println(str.indexOf('a'));
   

   0
   1
   2
   3
   
   Answer

   1
   (Explanation: indexOf('a') returns the index of the first occurrence of ‘a’, which is at index 1.)

10. What does the method String.format() do?

    String result = String.format("The number is: %d", 10);
    System.out.println(result);
    

    Converts numbers to string
    Formats the string to include variables
    Replaces all occurrences of a substring
    Appends strings
    
    Answer

    Formats the string to include variables
    (Explanation: String.format() allows formatting strings by inserting variables like numbers into placeholders.)

11. What will the following code print?

    String str = "  Hello World  ";
    System.out.println(str.trim().toUpperCase());
    

    HELLO WORLD
    Hello World
    HELLO WORLD
    Hello World
    
    Answer

    HELLO WORLD
    (Explanation: trim() removes leading and trailing spaces, and toUpperCase() converts the string to uppercase.)

12. What will the following code output?

    String str = "Java Programming";
    System.out.println(str.contains("Pro"));
    

    true
    false
    Error
    true false
    
    Answer

    true
    (Explanation: contains("Pro") checks if “Pro” is a part of the string and returns true.)

13. What does the following code do?

    String str = "Java";
    System.out.println(str.substring(1, 3));
    

    av
    Ja
    va
    J
    
    Answer

    av
    (Explanation: substring(1, 3) extracts the substring starting from index 1 and ending at index 3, which is “av”.)

14. What is the result of the following expression?

    String str = "Java";
    boolean result = str.startsWith("J");
    System.out.println(result);
    

    true
    false
    Error
    true false
    
    Answer

    true
    (Explanation: startsWith("J") checks if the string starts with the specified character ‘J’ and returns true.)

15. What is the return value of the following method call?

    String str = "Java";
    System.out.println(str.length());
    

    3
    4
    5
    0
    
    Answer

    4
    (Explanation: length() returns the number of characters in the string “Java”, which is 4.)

16. What will the following code print?

    String str = "Hello";
    System.out.println(str.equals("hello"));
    

    true
    false
    Error
    true false
    
    Answer

    false
    (Explanation: equals() is case-sensitive, so “Hello” is not equal to “hello”.)

17. What will the following code output?

    String str = "Java Programming";
    System.out.println(str.indexOf("Prog"));
    

    0
    1
    5
    -1
    
    Answer

    5
    (Explanation: indexOf("Prog") returns the index where the substring “Prog” begins, which is 5.)

18. What will this code print?

    String str = "Java";
    System.out.println(str.replace('a', 'o'));
    

    Jovo
    Jova
    Java
    Jovo
    
    Answer

    Jovo
    (Explanation: replace('a', 'o') replaces all occurrences of ‘a’ with ‘o’, resulting in “Jovo”.)

19. What is the return type of the method toCharArray()?

    String str = "Java";
    char[] result = str.toCharArray();
    

    String
    char[]
    char
    boolean
    
    Answer

    char[]
    (Explanation: toCharArray() converts the string into an array of characters and returns it.)

20. What does the method str.equalsIgnoreCase("java") return when the string is “JAVA”?

    String str = "JAVA";
    System.out.println(str.equalsIgnoreCase("java"));
    

    true
    false
    Error
    true false
    
    Answer

    true
    (Explanation: equalsIgnoreCase() compares two strings ignoring case, so “JAVA” equals “java”.)

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Slightly harder MCQs

Here are 20 more MCQs with code snippets that involve more than one method call, where the result of one method call is supplied to another:

1. What will the following code print?

    String str = "  Java Programming  ";
    System.out.println(str.trim().toUpperCase());
   

   JAVA PROGRAMMING
   Java Programming
   JAVA programming
   JAVA PROGRAMMING
   
   Answer

   JAVA PROGRAMMING
   (Explanation: trim() removes leading and trailing spaces, and toUpperCase() converts the string to uppercase.)

2. What will the following code output?

    String str = "Java Programming";
    System.out.println(str.substring(5).toLowerCase());
   

   programming
   Java programming
   JAVA PROGRAMMING
   Java programming
   
   Answer

   programming
   (Explanation: substring(5) extracts the substring starting at index 5, and toLowerCase() converts it to lowercase.)

3. What is the result of the following code?

    String str = "Java Programming";
    System.out.println(str.replace("Java", "Python").toLowerCase());
   

   python programming
   Python programming
   Java programming
   python Programming
   
   Answer

   python programming
   (Explanation: replace("Java", "Python") replaces “Java” with “Python” and toLowerCase() converts the string to lowercase.)

4. What will the following code print?

    String str = "    Hello World   ";
    System.out.println(str.trim().substring(0, 5));
   

   Hello
   Hello World
   Hello
   World
   
   Answer

   Hello
   (Explanation: trim() removes leading and trailing spaces, and substring(0, 5) extracts the first five characters.)

5. What is the output of the following code?

    String str = "Java Programming";
    System.out.println(str.substring(0, 4).toUpperCase());
   

   JAVA
   Java
   JAV
   JAVA programming
   
   Answer

   JAVA
   (Explanation: substring(0, 4) extracts “Java”, and toUpperCase() converts it to “JAVA”.)

6. What will be the output of this code?

    String str = "Hello";
    System.out.println(str.toLowerCase().replace('h', 'j'));
   

   hello
   jello
   Hello
   Jello
   
   Answer

   jello
   (Explanation: toLowerCase() converts “Hello” to “hello”, and replace('h', 'j') replaces ‘h’ with ‘j’.)

7. What does the following code print?

    String str = "Java";
    System.out.println(str.concat(" Programming").toUpperCase());
   

   JAVA
   Java Programming
   JAVA PROGRAMMING
   Java Programming
   
   Answer

   JAVA PROGRAMMING
   (Explanation: concat(" Programming") adds “ Programming” to “Java”, and toUpperCase() converts the result to uppercase.)

8. What will the output of the following code be?

    String str = "Java";
    System.out.println(str.substring(1).replace('a', 'o'));
   

   Jova
   Java
   Jovo
   Jaa
   
   Answer

   Jovo
   (Explanation: substring(1) removes the first character ‘J’, resulting in “ava”, and replace('a', 'o') changes ‘a’ to ‘o’, resulting in “Jovo”.)

9. What does the following code print?

    String str = "  Hello World  ";
    System.out.println(str.trim().substring(0, 4).toUpperCase());
   

   HELLO
   Hello
   Hell
   WORLD
   
   Answer

   HELL
   (Explanation: trim() removes the spaces, substring(0, 4) extracts “Hell”, and toUpperCase() converts it to “HELL”.)

10. What is the result of the following?

    String str = "Java Programming";
    System.out.println(str.substring(5, 15).toLowerCase().replace("programming", "rocks"));
    

    programming rocks
    programming
    rocks
    programming
    
    Answer

    rocks
    (Explanation: substring(5, 15) gives “Programming”, toLowerCase() converts it to “programming”, and replace("programming", "rocks") changes it to “rocks”.)

11. What will the following code output?

    String str = "Java";
    System.out.println(str.toUpperCase().substring(1, 3));
    

    JA
    AV
    VA
    JAVA
    
    Answer

    VA
    (Explanation: toUpperCase() converts “Java” to “JAVA”, and substring(1, 3) extracts “VA”.)

12. What does the following code print?

    String str = "  Hello World  ";
    System.out.println(str.trim().replace("World", "Java").toLowerCase());
    

    hello world
    hello java
    hello WORLD
    hello java world
    
    Answer

    hello java
    (Explanation: trim() removes leading/trailing spaces, replace("World", "Java") replaces “World” with “Java”, and toLowerCase() converts it to lowercase.)

13. What is the result of this code?

    String str = "Java Programming";
    System.out.println(str.replace("a", "o").substring(5));
    

    ovo Progrmming
    oJava Programming
    Java Programming
    oProgrmming
    
    Answer

    o Progrmming
    (Explanation: replace("a", "o") changes “Java Programming” to “Jovo Progrmming”, and substring(5) removes the first 5 characters.)

14. What will the output be of this code?

    String str = "Java Programming";
    System.out.println(str.substring(5).replace('a', 'o'));
    

    Java Progrogramming
    Jovo Progrogramming
    Progrogramming
    Progrogramming
    
    Answer

    Jovo Progrogramming
    (Explanation: substring(5) extracts “Programming”, and replace('a', 'o') changes ‘a’ to ‘o’.)

15. What does the following code print?

    String str = "Hello";
    System.out.println(str.concat(" World").toUpperCase());
    

    HELLO WORLD
    hello world
    HELLO
    Hello World
    
    Answer

    HELLO WORLD
    (Explanation: concat(" World") appends “ World” to “Hello”, and toUpperCase() converts it to “HELLO WORLD”.)

16. What will the following code output?

    String str = "Java";
    System.out.println(str.toLowerCase().replace('a', 'o').substring(1, 3));
    

    vo
    Oa
    va
    Jo
    
    Answer

    vo
    (Explanation: toLowerCase() converts “Java” to “java”, replace('a', 'o') changes ‘a’ to ‘o’, and substring(1, 3) extracts “vo”.)

17. What will the following code print?

    String str = "Java Programming";
    System.out.println(str.substring(5, 10).toUpperCase().concat(" is fun"));
    

    PROGRAMMING is fun
    PROGR is fun
    Program is fun
    PROGRAM is fun
    
    Answer

    PROGRAM is fun
    (Explanation: substring(5, 10) extracts “Progr”, toUpperCase() converts it to “PROGR”, and concat(" is fun") appends “ is fun”.)

18. What does this code print?

    String str = "  Hello World  ";
    System.out.println(str.trim().substring(6).toLowerCase());
    

    world
    hello world
    Hello world
    hello
    
    Answer

    world
    (Explanation: trim() removes spaces, substring(6) extracts “World”, and toLowerCase() converts it to “world”.)

19. What will the following code print?

    String str = "Hello";
    System.out.println(str.substring(1).toUpperCase().replace('E', 'O'));
    

    Ollo
    Ollo
    HELLO
    HOLO
    
    Answer

    Ollo
    (Explanation: substring(1) extracts “ello”, toUpperCase() converts it to “ELLO”, and replace('E', 'O') changes ‘E’ to ‘O’, resulting in “Ollo”.)

20. What is the result of the following code?

    String str = "Java Programming";
    System.out.println(str.substring(5, 10).toLowerCase().replace('r', 'l'));
    

    progLamming
    proGLamming
    programming
    proLamming
    
    Answer

    proglamming
    (Explanation: substring(5, 10) extracts “Prog”, toLowerCase() converts it to “prog”, and replace('r', 'l') changes ‘r’ to ‘l’, resulting in “proglamming”.)

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Tricky MCQs

Here are 20 tricky and slightly confusing questions based on Java String methods:

1. What does the following code print?

    String str = "Java";
    System.out.println(str.substring(2, 2));
   

   Empty string
   J
   a
   Error
   
   Answer

   Empty string
   (Explanation: substring(2, 2) extracts from index 2 to index 2, so no characters are selected, resulting in an empty string.)

2. What is the result of the following code?

    String str = "Java Programming";
    System.out.println(str.substring(5, 20));
   

   Programming
   Error
   Java Programming
   Progr
   
   Answer

   Error
   (Explanation: substring(5, 20) will throw an error because the second index exceeds the length of the string.)

3. What is the output of the following code?

    String str = "Java Programming";
    System.out.println(str.replace('a', 'o').substring(4, 10));
   

   Progra
   Progr
   Prorg
   Prora
   
   Answer

   Prorg
   (Explanation: replace('a', 'o') replaces ‘a’ with ‘o’, so “Java Programming” becomes “Jovo Progromming”. substring(4, 10) extracts “Prorg”.)

4. What will the output be?

    String str = "Java";
    System.out.println(str.indexOf('a', 2));
   

   1
   2
   3
   -1
   
   Answer

   3
   (Explanation: indexOf('a', 2) starts searching from index 2, and the next ‘a’ is at index 3.)

5. What is the output of this code?

    String str = "Java";
    System.out.println(str.charAt(5));
   

   Error
   a
   J
   IndexOutOfBoundsException
   
   Answer

   Error
   (Explanation: charAt(5) is out of bounds since the string “Java” has a length of 4.)

6. What will the output of this code be?

    String str = "Java";
    System.out.println(str.substring(4));
   

   Empty string
   Java
   a
   Error
   
   Answer

   Empty string
   (Explanation: substring(4) starts at index 4, but the string has only 4 characters, so it returns an empty string.)

7. What will the following code print?

    String str = "Java";
    System.out.println(str.replace("av", "o"));
   

   Jo
   Java
   Joo
   Javo
   
   Answer

   Joo
   (Explanation: replace("av", "o") replaces “av” with “o”, resulting in “Joo”.)

8. What will the following code output?

    String str = "Java";
    System.out.println(str.indexOf("va", 1));
   

   1
   2
   3
   -1
   
   Answer

   2
   (Explanation: indexOf("va", 1) starts searching from index 1, and “va” is found starting at index 2.)

9. What is the output of this code?

    String str = "Java";
    System.out.println(str.replace("a", "o").substring(1, 3));
   

   Jovo
   ovo
   Ova
   Jo
   
   Answer

   vo
   (Explanation: replace("a", "o") changes “Java” to “Jovo”, and substring(1, 3) extracts “vo”.)

10. What will be the output of this code?

    String str = "Java";
    System.out.println(str.charAt(str.length() - 1));
    

    J
    a
    Error
    IndexOutOfBoundsException
    
    Answer

    a
    (Explanation: str.length() - 1 calculates the index of the last character, which is ‘a’.)

11. What is the output of this code?

    String str = "Java Programming";
    System.out.println(str.substring(5, 5));
    

    Programming
    Empty string
    Java Programming
    Error
    
    Answer

    Empty string
    (Explanation: substring(5, 5) extracts a substring starting and ending at index 5, so the result is an empty string.)

12. What will be the output of this code?

    String str = "Java";
    System.out.println(str.toLowerCase().concat(" Programming").substring(0, 10));
    

    java Program
    java progra
    Java Program
    java program
    
    Answer

    java program
    (Explanation: toLowerCase() converts “Java” to “java”, concat(" Programming") appends “ Programming”, and substring(0, 10) extracts “java progra”.)

13. What does this code output?

    String str = "Hello World";
    System.out.println(str.indexOf('o', 5));
    

    5
    7
    4
    6
    
    Answer

    7
    (Explanation: indexOf('o', 5) searches for ‘o’ starting from index 5, and the next ‘o’ is at index 7.)

14. What will this code print?

    String str = "Java Programming";
    System.out.println(str.replace(" ", ""));
    

    Java Programming
    JavaProgramming
    Error
    Java
    
    Answer

    JavaProgramming
    (Explanation: replace(" ", "") removes all spaces from the string.)

15. What is the output of this code?

    String str = "Java Programming";
    System.out.println(str.replace("a", "o").substring(5, 15).toUpperCase());
    

    OPROGRAMMING
    PROGR OGRAMMING
    PROGR OGRAMMING
    PROGRAMMING
    
    Answer

    OPROGRAMMING
    (Explanation: replace("a", "o") replaces “a” with “o”, then substring(5, 15) extracts “Programming”, and toUpperCase() converts it to uppercase.)

16. What is the result of the following?

    String str = "Hello";
    System.out.println(str.substring(1, 3).toUpperCase());
    

    EL
    He
    lo
    HEL
    
    Answer

    EL
    (Explanation: substring(1, 3) extracts “el”, and toUpperCase() converts it to “EL”.)

17. What will this code print?

    String str = "Java Programming";
    System.out.println(str.indexOf("Java") == 0);
    

    true
    false
    Error
    false
    
    Answer

    true
    (Explanation: indexOf("Java") == 0 checks if “Java” starts at index 0, which is true.)

18. What does this code print?

    String str = "Java";
    System.out.println(str.charAt(str.length()));
    

    a
    Error
    Java
    IndexOutOfBoundsException
    
    Answer

    Error
    (Explanation: charAt(str.length()) causes an error because index str.length() is out of bounds.)

19. What will the following code print?

    String str = "   Hello ";
    System.out.println(str.trim().length());
    

    5
    6
    7
    4
    
    Answer

    5
    (Explanation: trim() removes the spaces, leaving “Hello”, and the length is 5.)

20. What does this code print?

    String str = "Java Programming";
    System.out.println(str.substring(5, 20));
    

    Error
    Progr
    Programming
    Program
    
    Answer

    Error
    (Explanation: The second argument in substring(5, 20) is greater than the length of the string, so it throws an error.)

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