Java MCQ Questions – Page 121 of 200

Q: Which of these primitive types can be implicitly converted to a `double`?

C) byte, short, int, long, float. A `double` is the largest floating-point type and can implicitly accommodate values from `byte`, `short`, `int`, `long`, and `float` without loss of magnitude (though precision might be affected for very large long values).

Q: What is the output of this code?

A) Description: null Quantity: 0 In Stock: false. When an object is created, its instance variables are automatically initialized to their default values if not explicitly assigned. For `String` (object type), the default is `null`; for `int` (numeric primitive), it's `0`; and for `boolean` (boolean primitive), it's `false`.

Q: What kind of error will occur when compiling or running the following Java code?

A) java.lang.StringIndexOutOfBoundsException. The `replace(int start, int end, String str)` method throws a `StringIndexOutOfBoundsException` if `start` is greater than `end`. In this case, `10 > 5` which violates the method contract.

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

A) Compilation error: Cannot assign a value to final variable 'sku'.. The 'sku' field is declared as 'final', meaning its value can only be assigned once, either at declaration or in the constructor. Attempting to reassign 'sku' in the 'renameProduct' method will cause a compilation error.

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

A) Compile-time error. The integer literal `30` can be widened to both `long` and `float`. Since neither `long` nor `float` is more specific than the other, the call is ambiguous, resulting in a compile-time error.

Q: What is the output of this code?

A) 20. The 'try' block sets 'value' to 10. Since there's no exception, the 'finally' block executes, overwriting 'value' to 20. This final value is then printed.

Q: What kind of error will occur when executing the following Java code?

D) Runtime Error: java.lang.IllegalMonitorStateException. Similar to `wait()`, the `notify()` method must be called within a `synchronized` block or method on the object whose monitor the current thread holds. Failing to do so throws a `java.lang.IllegalMonitorStateException`.

Q: What is the valid range for a thread's priority in Java, and what is its default value?

B) 1 to 10; default is 5.. Thread priorities in Java range from `Thread.MIN_PRIORITY` (1) to `Thread.MAX_PRIORITY` (10), with `Thread.NORM_PRIORITY` (5) being the default priority for a newly created thread.

Q: Given the following Java code snippet: java String s1 = "hello"; String s2 = "hello"; String s3 = new String("hello"); System.out.println(s1 == s2); System.out.println(s1 == s3); What will be the output?

B) true, false. `s1` and `s2` refer to the same literal string in the String pool, so `s1 == s2` is true. `s3` is created using `new String()`, which always creates a new object on the heap, making `s1 == s3` false as they are distinct objects.

Q: What is the content of 'auto_closed.txt' after this code executes?

C) This is automatically closed.. The try-with-resources statement ensures that the `FileWriter` resource is automatically closed at the end of the try block, even if an exception occurs. This automatic closing flushes and writes the content to the file.

Q2401 easy

Which of these primitive types can be implicitly converted to a `double`?

Q2402 medium code output

What is the output of this code?

java

class Item {
    String description;
    int quantity;
    boolean inStock;
}

public class Main {
    public static void main(String[] args) {
        Item item = new Item();
        System.out.println("Description: " + item.description);
        System.out.println("Quantity: " + item.quantity);
        System.out.println("In Stock: " + item.inStock);
    }
}

Q2403 hard code error

What kind of error will occur when compiling or running the following Java code?

java

public class SBError {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("JavaProgramming"); // Length 15
        String replacement = "Awesome";
        // Attempt to replace from index 10 to 5 (start > end)
        sb.replace(10, 5, replacement);
        System.out.println(sb);
    }
}

Q2404 medium code error

What is the error in the following Java code?

java

class Product {
    private final String sku;
    private String name;

    public Product(String sku, String name) {
        this.sku = sku;
        this.name = name;
    }

    public void renameProduct(String newName) {
        this.sku = newName; // Attempt to modify final field
    }

    public String getName() { return name; }
    public String getSku() { return sku; }
}

public class Inventory {
    public static void main(String[] args) {
        Product p = new Product("P123", "Laptop");
        p.renameProduct("Desktop");
    }
}

Q2405 easy code output

What is the output of this Java code snippet?

java

public class OverloadDemo6 {
    void execute(long l) {
        System.out.println("Executing long: " + l);
    }
    void execute(float f) {
        System.out.println("Executing float: " + f);
    }
    public static void main(String[] args) {
        OverloadDemo6 obj = new OverloadDemo6();
        obj.execute(30);
    }
}

Q2406 easy code output

What is the output of this code?

java

public class Main {
    public static void main(String[] args) {
        int value = 0;
        try {
            value = 10;
        } finally {
            value = 20;
        }
        System.out.println(value);
    }
}

Q2407 easy code error

What kind of error will occur when executing the following Java code?

java

public class MyNotifier {
    private final Object lock = new Object();

    public void signalWaitingThread() {
        // Calling notify() without holding the monitor for 'lock'
        lock.notify();
    }

    public static void main(String[] args) {
        MyNotifier notifier = new MyNotifier();
        new Thread(notifier::signalWaitingThread).start();
    }
}

Q2408 medium

What is the valid range for a thread's priority in Java, and what is its default value?

Q2409 medium

Given the following Java code snippet: java String s1 = "hello"; String s2 = "hello"; String s3 = new String("hello"); System.out.println(s1 == s2); System.out.println(s1 == s3); What will be the output?

Q2410 medium code output

What is the content of 'auto_closed.txt' after this code executes?

java

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

public class TryWithResourcesTest {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("auto_closed.txt")) {
            writer.write("This is automatically closed.");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
        // No explicit close() is called here.
    }
}

Q2411 hard code error

What is the output of this code?

java

import java.util.LinkedList;
import java.util.Arrays;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<Double> values = new LinkedList<>(Arrays.asList(1.1, 2.2, 3.3));
        values.remove(values.size()); // Invalid index for remove
        System.out.println(values);
    }
}

Q2412 easy

When creating a thread by extending the `Thread` class, which of the following is a mandatory step?

Q2413 hard code error

What is the error encountered when running this Java code?

java

public class PrimitiveArrayCastError {
    public static void main(String[] args) {
        Object obj = new Integer[]{1, 2, 3};
        int[] intArray = (int[]) obj;
        System.out.println(intArray[0]);
    }
}

Q2414 medium code output

What does this Java code print to the console?

java

import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;

public class Test {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        Consumer<String> addToList = names::add;
        Consumer<String> printName = System.out::println;

        addToList.accept("Alice");
        printName.accept("Bob");
        System.out.println(names.size());
    }
}

Q2415 medium code output

What is the output of this Java code?

java

class DaemonTask implements Runnable {
    public void run() {
        try {
            System.out.println("Daemon thread started.");
            Thread.sleep(1000); // Simulate long running task
            System.out.println("Daemon thread finished.");
        } catch (InterruptedException e) {
            System.out.println("Daemon interrupted.");
        }
    }
}
public class Main {
    public static void main(String[] args) throws InterruptedException {
        Thread daemonThread = new Thread(new DaemonTask());
        daemonThread.setDaemon(true);
        daemonThread.start();
        Thread.sleep(50); // Give daemon a chance to start
        System.out.println("Main thread exiting.");
    }
}

Q2416 medium code output

What will this Java code print?

java

public class StringBufferTest {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Test");
        String s = "Java";
        sb.append(s).insert(sb.length(), "!");
        System.out.print(sb.length() + " " + sb.capacity());
    }
}

Q2417 easy code error

What error will occur when compiling the following Java code?

java

public class Main {
    public static void main(String[] args) {
        int x = 7;
        if (5 < x < 10) {
            System.out.println("X is between 5 and 10.");
        } else {
            System.out.println("X is not between 5 and 10.");
        }
    }
}

Q2418 easy

How do you create a new single-dimensional integer array of size 5 named `scores`?

Q2419 easy

What does a `Thread` object represent in Java?

Q2420 hard

Considering memory footprint and garbage collection overhead, how does `java.util.LinkedList` compare to `java.util.ArrayList` for storing a large number of objects?

☕ Java MCQ Questions – Page 121