Java MCQ Questions – Page 187 of 200

Q: What does this code print?

B) [2.2, 3.3]. Values 1.1 and 2.2 are added to the queue. `poll()` removes 1.1 (the head). Then 3.3 is offered. The queue now contains 2.2 followed by 3.3. The `toString()` method of ArrayDeque prints the elements in insertion order.

Q: What is the output of this code?

A) Before: 0 After: 5. BufferedWriter buffers data internally. Data is only written to the underlying StringWriter when flush() or close() is explicitly called or the buffer becomes full. Therefore, sw.toString() returns an empty string before bw.close(), and the full string after.

Q: What compilation error will this Java code produce?

A) Error: break with value is not allowed outside of switch expressions. Using `break` with a value (e.g., `break 10;`) is specific to `switch` *expressions* (Java 14+) where it acts like `yield`. In a `switch` *statement*, `break` does not accept a value and will cause a compilation error.

Q: What is the error in this Java code?

B) Compile-time error: cannot find symbol (method bark() on type Animal). Even though `myAnimal` refers to a `Dog` object, its declared type is `Animal`. The compiler only allows methods declared in the `Animal` class (or its supertypes) to be called directly through `myAnimal`.

Q: What error will this Java code produce during compilation?

A) Compilation Error: illegal start of expression / Array dimension missing. In Java, multi-dimensional arrays are accessed using separate square brackets for each dimension (e.g., `matrix[row][col]`), not a single set of brackets with a comma (`matrix[row,col]`). This is a syntax error detected by the compiler.

Q: What is the output of this Java code?

A) -126. When casting an int value 130 to a byte, which has a range of -128 to 127, an overflow occurs. The value wraps around, resulting in -126.

Q: What is the output of this Java code snippet?

A) Both conditions met. The outer `if` condition `x 5` (10 > 5) is also true, leading to 'Both conditions met' being printed.

Q: What is the output of this Java code?

A) [Apple, Cherry]. The code iterates through the list. When 'Banana' is encountered, `it.remove()` is called, which correctly removes the last element returned by `next()` from the underlying collection. The final list contains 'Apple' and 'Cherry'.

Q: Which requirement must `case` labels satisfy in a Java `switch` statement or expression?

B) They must be unique and compile-time constant values.. `case` labels must be unique constant values that can be determined at compile time. This includes literals, `final` variables initialized with a literal, or enum constants.

Q: In a traditional Java `for` loop, what happens if any of the three parts (initialization, condition, or update) are omitted?

C) The omitted initialization or update is simply skipped, and an omitted condition defaults to `true`. The initialization and update parts can be omitted, in which case nothing happens for that part. If the condition is omitted, it defaults to `true`, potentially creating an infinite loop.

Q3721 easy code output

What does this code print?

java

import java.util.ArrayDeque;
import java.util.Queue;

public class Main {
    public static void main(String[] args) {
        Queue<Double> values = new ArrayDeque<>();
        values.offer(1.1);
        values.offer(2.2);
        values.poll();
        values.offer(3.3);
        System.out.println(values);
    }
}

Q3722 hard code output

What is the output of this code?

java

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.StringWriter;

public class Test {
    public static void main(String[] args) throws IOException {
        StringWriter sw = new StringWriter();
        BufferedWriter bw = new BufferedWriter(sw);
        bw.write("Hello");
        String contentBeforeClose = sw.toString();
        bw.close();
        String contentAfterClose = sw.toString();
        System.out.println("Before: " + contentBeforeClose.length());
        System.out.println("After: " + contentAfterClose.length());
    }
}

Q3723 medium code error

What compilation error will this Java code produce?

java

public class SwitchError {
    public static void main(String[] args) {
        int day = 4;
        switch (day) {
            case 1: {
                System.out.println("Workday");
                break 10; // Incorrect usage of break with value in a statement
            }
            default:
                System.out.println("Other day");
        }
    }
}

Q3724 easy code error

What is the error in this Java code?

java

class Animal {
    public void eat() {
        System.out.println("Animal eats");
    }
}

class Dog extends Animal {
    public void bark() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myAnimal = new Dog();
        myAnimal.bark(); // Line 14
    }
}

Q3725 easy code error

What error will this Java code produce during compilation?

java

public class ArrayError {
    public static void main(String[] args) {
        int[][] matrix = {{1, 2}, {3, 4}};
        System.out.println(matrix[0,1]);
    }
}

Q3726 easy code output

What is the output of this Java code?

java

public class TypeCast {
    public static void main(String[] args) {
        int num = 130;
        byte b = (byte) num;
        System.out.println(b);
    }
}

Q3727 easy code output

What is the output of this Java code snippet?

java

public class Main {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        if (x < 10) {
            if (y > 5) {
                System.out.println("Both conditions met");
            }
        }
    }
}

Q3728 easy code output

What is the output of this Java code?

java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");
        Iterator<String> it = fruits.iterator();
        while (it.hasNext()) {
            String fruit = it.next();
            if (fruit.equals("Banana")) {
                it.remove();
            }
        }
        System.out.println(fruits);
    }
}

Q3729 medium

Which requirement must `case` labels satisfy in a Java `switch` statement or expression?

Q3730 medium

In a traditional Java `for` loop, what happens if any of the three parts (initialization, condition, or update) are omitted?

Q3731 easy code error

What kind of error will occur when compiling this Java code?

java

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        BufferedWriter bw;
        try {
            // bw is not guaranteed to be initialized here before use
            bw.write("Hello");
            bw = new BufferedWriter(new FileWriter("output.txt"));
            bw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q3732 medium code output

What is printed by this Java code?

java

class LoginFailedException extends Exception {
    public LoginFailedException(String message, Throwable cause) {
        super(message, cause);
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            try {
                Integer.parseInt("abc"); // Throws NumberFormatException
            } catch (NumberFormatException e) {
                throw new LoginFailedException("Login service unavailable", e);
            }
        } catch (LoginFailedException e) {
            System.out.println("Root Cause: " + e.getCause().getClass().getSimpleName());
        }
    }
}

Q3733 medium code error

What error will occur when running this Java code snippet?

java

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Test {
    public static void main(String[] args) {
        Map<String, String> config = new HashMap<>();
        config.put("setting1", "value1");
        config.put("setting2", "value2");
        config.put("setting3", "value3");

        Iterator<Map.Entry<String, String>> iterator = config.entrySet().iterator();
        
        if (iterator.hasNext()) {
            iterator.next(); // Move to the first element
            iterator.remove(); // Remove the first element
            iterator.remove(); // Attempt to remove again without calling next()
        }
        System.out.println(config.size());
    }
}

Q3734 hard code error

What is the output of this code?

java

import java.io.File;
import java.io.IOException;

public class MkdirParentAsFile {
    public static void main(String[] args) {
        File parentFile = new File("parent_as_file.txt");
        File childDir = new File(parentFile, "child_dir");
        try {
            parentFile.createNewFile(); // Create a regular file at parent path
            boolean success = childDir.mkdir(); // Attempt to create a directory with a file as its parent
            System.out.println("mkdir success: " + success);
        } catch (IOException e) {
            System.out.println("Error: " + e.getClass().getSimpleName() + ": " + e.getMessage());
        } finally {
            parentFile.delete(); // Clean up
        }
    }
}

Q3735 easy code error

Identify the compile-time error in the provided Java snippet related to method overloading.

java

import java.io.IOException;

class Worker {
    void performTask() {
        System.out.println("Task performed.");
    }

    void performTask() throws IOException {
        System.out.println("Task with potential IO error performed.");
    }
}

Q3736 easy code output

What will be the content of the file 'output.txt' after this code executes?

java

import java.io.FileWriter;
import java.io.IOException;

public class FileWriterTest {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt")) {
            writer.write(65);
            writer.write(97);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q3737 hard code error

What compilation error will occur in the `calculateValue` method?

java

class Test {
    public int calculateValue() {
        int i = 0;
        do {
            i++;
            // No explicit return statement within the loop
        } while (true); // An infinite loop
        // The compiler expects a reachable return statement here
    }
}

Q3738 medium

What does the `mark()` method in `BufferedReader` allow you to do?

Q3739 hard code error

What is the error encountered when running this Java code?

java

import java.io.FileReader;
import java.io.IOException;
import java.io.File;

public class FileReaderError4 {
    public static void main(String[] args) {
        File file = new File("test_fr4.txt");
        try {
            file.createNewFile();
            try (FileReader fr = new FileReader(file)) {
                // FileReader typically does not support mark/reset
                if (!fr.markSupported()) {
                    fr.mark(10); // Attempt to mark when not supported
                }
                System.out.println("Mark set");
            }
        } catch (IOException e) {
            System.err.println(e.getClass().getSimpleName() + ": " + e.getMessage());
        } finally {
            file.delete();
        }
    }
}

Q3740 hard code error

What is the error in the execution of this Java code snippet?

java

public class BuilderError {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("World");
        sb.replace(10, 5, "Hello");
        System.out.println(sb);
    }
}

☕ Java MCQ Questions – Page 187