Java MCQ Questions – Page 184 of 200

Q: In highly constrained environments or low-level libraries, developers might consider creating custom `Error` subclasses instead of `Exception` subclasses. Under what specific, rare circumstances might creating a custom `Error` be justified over a custom `RuntimeException`?

C) When dealing with fundamental, unrecoverable system problems like JVM corruption, out-of-memory, or severe resource exhaustion that the application cannot reasonably handle.. Custom `Error` subclasses are extremely rare and typically reserved for situations mirroring JVM-level `Error`s (like `OutOfMemoryError`), signifying critical, unrecoverable system problems where the application's integrity is compromised and continuation is not feasible or safe.

Q: What is the output of this code?

A) 20, 10. This is a classic XOR swap algorithm without using a temporary variable. Initial: a=10, b=20. 1. `a = a ^ b;` => `a = 10 ^ 20` (binary `01010 ^ 10100 = 11110 = 30`). Now a=30, b=20. 2. `b = a ^ b;` => `b = 30 ^ 20` (binary `11110 ^ 10100 = 01010 = 10`). Now a=30, b=10. 3. `a = a ^ b;` => `a = 30 ^ 10` (binary `11110 ^ 01010 = 10100 = 20`). Now a=20, b=10. The values are swapped.

Q: What is the output of this code?

A) T1 started. Main joining T1... Main thread interrupted while joining! Main exiting.. The main thread interrupts *itself* using `Thread.currentThread().interrupt()` before calling `t1.join()`. As a result, `t1.join()` immediately throws an `InterruptedException` in the main thread because the main thread's interrupted status is already set. T1 is not interrupted and continues its sleep.

Q: To compare two arrays, `array1` and `array2`, for element-by-element equality in Java, which method should be used?

C) `java.util.Arrays.equals(array1, array2)`. `array1 == array2` checks if both variables refer to the *same* array object. `array1.equals(array2)` is not overridden for arrays and behaves like `==`. `Arrays.equals()` correctly compares the contents of two arrays element by element.

Q: What is the runtime error in the following Java code snippet?

A) Runtime error: java.lang.ClassCastException.. While using a raw `ArrayList` allows adding any object, attempting to cast a `String` (which was added) to an `Integer` during retrieval will result in a `ClassCastException` at runtime.

Q: What error occurs when running this Java code?

A) Runtime error: java.lang.RuntimeException: Exception from finally. When an exception is thrown from a `finally` block, it will suppress any previously pending exception (including one already caught and processed) and will be the exception that propagates out of the method. `RuntimeException` is unchecked, so it compiles, but causes a runtime error.

Q: What is the output of this Java code?

A) Produced 1 Consumed 1 Produced 2 Consumed 2. The `ArrayBlockingQueue` has capacity 1. `put()` blocks when full, `take()` blocks when empty. The `Thread.sleep(100)` orchestrates the output by letting the producer try to put before the consumer takes, unblocking the producer to put the next item, which the consumer then takes.

Q: What is the output of this code?

C) Child bar. An `Animal` reference `p` is upcasted to `Child` type `c`. This allows `c` to call methods specific to `Child`, such as `bar()`, which prints "Child bar".

Q: What is the output of this Java code?

A) 133. The `Integer::parseInt` method reference points to the static `parseInt` method of the `Integer` class. It converts the string "123" to an integer, which is then added to 10, resulting in 133.

Q: Assuming `System.getProperty("user.dir")` is `/tmp/path_resolution_base` (or similar temporary path) and the file is created, what is the output of this Java code snippet?

A) getPath(): true getAbsolutePath() contains '..': true getCanonicalPath() matches actual: true. `getPath()` returns the string used to create the File object, including `..` and `.`. `getAbsolutePath()` resolves the path relative to the current working directory but doesn't necessarily normalize `.` and `..`. `getCanonicalPath()` fully resolves all `.` `..` and symbolic links, resulting in the shortest, unambiguous path to the file, which will match the actual file's canonical path.

Q3661 hard

In highly constrained environments or low-level libraries, developers might consider creating custom `Error` subclasses instead of `Exception` subclasses. Under what specific, rare circumstances might creating a custom `Error` be justified over a custom `RuntimeException`?

Q3662 hard code output

What is the output of this code?

java

public class OperatorChallenge {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        a = a ^ b;
        b = a ^ b;
        a = a ^ b;
        System.out.println(a + ", " + b);
    }
}

Q3663 hard code output

What is the output of this code?

java

public class JoinInterruptTest {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            try {
                System.out.println("T1 started.");
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                System.out.println("T1 interrupted!");
            }
        });
        t1.start();
        Thread.sleep(100);
        try {
            System.out.println("Main joining T1...");
            Thread.currentThread().interrupt();
            t1.join();
        } catch (InterruptedException e) {
            System.out.println("Main thread interrupted while joining!");
        }
        System.out.println("Main exiting.");
    }
}

Q3664 medium

To compare two arrays, `array1` and `array2`, for element-by-element equality in Java, which method should be used?

Q3665 easy code error

What is the runtime error in the following Java code snippet?

java

import java.util.ArrayList;

public class Question9 {
    public static void main(String[] args) {
        ArrayList rawList = new ArrayList(); // Using raw type
        rawList.add("Hello");
        Integer val = (Integer) rawList.get(0);
        System.out.println(val);
    }
}

Q3666 medium code error

What error occurs when running this Java code?

java

import java.io.IOException;

public class FinallyBehavior {
    public static void main(String[] args) {
        try {
            System.out.println("Inside try");
            throw new IOException("Original IOException");
        } catch (IOException e) {
            System.out.println("Caught IOException: " + e.getMessage());
        } finally {
            System.out.println("Inside finally");
            throw new RuntimeException("Exception from finally");
        }
    }
}

Q3667 hard code output

What is the output of this Java code?

java

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

public class QueueTest {
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(1);

        new Thread(() -> {
            try {
                queue.put(1);
                System.out.println("Produced 1");
                queue.put(2);
                System.out.println("Produced 2");
            } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
        }).start();

        Thread.sleep(100);

        new Thread(() -> {
            try {
                System.out.println("Consumed " + queue.take());
                System.out.println("Consumed " + queue.take());
            } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
        }).start();

        Thread.sleep(500);
    }
}

Q3668 easy code output

What is the output of this code?

java

class Parent {
    public void foo() { System.out.print("Parent foo"); }
}

class Child extends Parent {
    public void foo() { System.out.print("Child foo"); }
    public void bar() { System.out.print("Child bar"); }
}

public class Main {
    public static void main(String[] args) {
        Parent p = new Child();
        Child c = (Child) p;
        c.bar();
    }
}

Q3669 medium code output

What is the output of this Java code?

java

import java.util.function.Function;

public class MethodRefTest {
    public static void main(String[] args) {
        Function<String, Integer> parser = Integer::parseInt;
        int result = parser.apply("123") + 10;
        System.out.println(result);
    }
}

Q3670 hard code output

Assuming `System.getProperty("user.dir")` is `/tmp/path_resolution_base` (or similar temporary path) and the file is created, what is the output of this Java code snippet?

java

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public class PathResolution {
    public static void main(String[] args) throws IOException {
        // Setup temporary directory structure for predictable results
        Path tempDir = Files.createTempDirectory("path_resolution_base");
        Path innerDir = Files.createDirectory(tempDir.resolve("inner"));
        Path targetFile = Files.createFile(innerDir.resolve("data.txt"));

        // File object constructed with '..' and '.'
        File complexPathFile = new File(innerDir.toFile(), "../inner/./data.txt");
        File actualFile = targetFile.toFile();

        System.out.println("getPath(): " + complexPathFile.getPath().contains("../inner/./data.txt"));
        System.out.println("getAbsolutePath() contains '..': " + complexPathFile.getAbsolutePath().contains(".."));
        System.out.println("getCanonicalPath() matches actual: " + complexPathFile.getCanonicalPath().equals(actualFile.getCanonicalPath()));

        Files.delete(targetFile);
        Files.delete(innerDir);
        Files.delete(tempDir);
    }
}

Q3671 medium

When the `read()` method of a `FileReader` returns -1, what does it signify?

Q3672 easy code error

What error will occur when running this Java code, assuming the file 'data.ser' was successfully created previously by serializing an `Integer` object?

java

import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("data.ser"))) {
            String data = (String) ois.readObject(); // Assume data.ser contains an Integer
            System.out.println("Deserialized: " + data);
        } catch (IOException | ClassNotFoundException e) {
            System.err.println(e.getClass().getSimpleName() + ": " + e.getMessage());
        }
    }
}

Q3673 hard code output

What is the output of this Java code?

java

import java.util.TreeMap;
import java.util.NavigableMap;

public class Test {
    public static void main(String[] args) {
        TreeMap<Integer, String> map = new TreeMap<>();
        map.put(10, "Ten");
        map.put(20, "Twenty");
        map.put(30, "Thirty");
        map.put(40, "Forty");

        NavigableMap<Integer, String> head = map.headMap(20, true); // <= 20
        NavigableMap<Integer, String> tail = map.tailMap(30, false); // > 30
        NavigableMap<Integer, String> emptyTail = map.tailMap(50, false); // No keys > 50

        System.out.println(head.keySet() + " " + tail.keySet() + " " + emptyTail.isEmpty());
    }
}

Q3674 easy code output

What does this Java code snippet print to the console?

java

public class LoopTest {
    public static void main(String[] args) {
        int repeat = 0;
        String message = "";
        do {
            message += "Java ";
            repeat++;
        } while (repeat < 2);
        System.out.print(message);
    }
}

Q3675 medium

Under what condition does a Java `while` loop continue its execution?

Q3676 easy code error

What error will this code produce?

java

public class LoopError {
    public static void main(String[] args) {
        int counter = 0;
        for (int counter = 0; counter < 3; counter++) {
            System.out.println(counter);
        }
    }
}

Q3677 medium code error

What is the result when compiling and running this Java code snippet?

java

import java.util.LinkedList;
import java.util.Queue;

public class QueueError {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        queue.addFirst("Hello"); // Method 'addFirst' is not part of the Queue interface
    }
}

Q3678 easy

Which method compares two strings for equality, ignoring case differences?

Q3679 easy code output

What is the output of this code?

java

public class StringTest {
    public static void main(String[] args) {
        String s = "  Hello World  ";
        System.out.println(s.trim());
    }
}

Q3680 hard code output

What does this Java code print, illustrating correct encapsulation using defensive copying in a getter?

java

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

class SecureData {
    private final List<String> dataLines;
    public SecureData(List<String> initialLines) {
        this.dataLines = new ArrayList<>(initialLines);
    }
    public List<String> getDataLines() {
        return new ArrayList<>(this.dataLines);
    }
}

public class Main {
    public static void main(String[] args) {
        List<String> originalLines = new ArrayList<>(List.of("Line 1", "Line 2"));
        SecureData data = new SecureData(originalLines);
        System.out.println("Initial internal data: " + data.getDataLines());
        
        List<String> retrievedLines = data.getDataLines();
        retrievedLines.add("Line 3 - external");
        
        System.out.println("Data after external modification attempt: " + data.getDataLines());
    }
}

☕ Java MCQ Questions – Page 184