Java MCQ Questions – Page 47 of 200

Q: What kind of runtime error or unexpected behavior will occur when running this Java code, primarily related to thread lifecycle?

C) The program will experience a deadlock and hang indefinitely.. The `Thread.suspend()` method (which is deprecated) does not release any locks that the target thread holds. In this scenario, `suspendedThread` acquires `lock` and then suspends itself while still holding the lock. When the main thread tries to acquire the same `lock`, it becomes `BLOCKED` indefinitely, leading to a deadlock as the main thread can never call `resume()`.

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

B) Incorrect syntax: the `do` block requires curly braces `{}` not parentheses `()`.`. The `do` statement requires its body to be enclosed in curly braces `{}`. Using parentheses `()` instead, as in `do (...)`, is a syntax error in Java for defining a block of code, leading to an 'unexpected token' compilation error.

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

A) Error: Cannot inherit from final class Vehicle. A class declared as 'final' cannot be extended. The 'Car' class attempts to extend 'Vehicle', which is a final class, leading to a compilation error.

Q: What is the output of this code?

A) ADnull. First `read()` prints 'A'. `skip(2)` skips 'B' and 'C'. The next `read()` prints 'D'. `skip(Long.MAX_VALUE)` skips all remaining characters ('EFG'). Finally, `readLine()` finds the end of the stream and returns `null`.

Q: What will be the output or error when running this code?

B) Compilation Error: variable `myCar` might not have been initialized. The reference `myCar` is declared but not initialized to an object or `null`. Java prevents using uninitialized local variables, resulting in a compilation error.

Q: What is the output of this Java code?

B) false true. Concatenation of `String` variables at runtime creates a new `String` object on the heap, so `s3 == s4` is `false`. However, `intern()` explicitly places the `String` into the string pool or returns the reference if it already exists, making `s3 == s5` `true`.

Q: Which method must a class implement when it implements the `Runnable` interface?

C) run(). The `Runnable` interface declares a single abstract method named `run()`, which contains the code that will be executed in the new thread.

Q: What compilation error will occur in the `Child` class?

A) `execute()` in `Child` cannot override `execute()` in `Parent`; overridden method does not throw `BaseException`.. When overriding a method, the subclass method cannot declare a checked exception that is a superclass of the exception declared in the superclass method. `BaseException` is a superclass of `SpecificException`, so `Child.execute()` cannot declare `throws BaseException` if `Parent.execute()` only declares `throws SpecificException`.

Q: What is the compile-time error in the following Java code?

A) Error: recursive constructor invocation. The constructor `MyClass()` calls `this(5)`, and the constructor `MyClass(int a)` in turn calls `this()`. This creates a direct cyclic dependency between the two constructors, which the Java compiler detects and flags as a 'recursive constructor invocation' error.

Q: What error occurs when running this code, assuming '.' is the current directory?

A) The program prints 'Error: . (Is a directory)' and exits.. A `FileReader` is designed to read actual files, not directories. Attempting to create a `FileReader` for a directory typically results in a `FileNotFoundException` (a subclass of `IOException`) with a message indicating it's a directory.

Q921 hard code error

What kind of runtime error or unexpected behavior will occur when running this Java code, primarily related to thread lifecycle?

java

public class SuspendResumeDemo {
    private static Object lock = new Object();
    private static Thread suspendedThread;

    public static void main(String[] args) throws InterruptedException {
        suspendedThread = new Thread(() -> {
            synchronized (lock) { // Acquires lock
                System.out.println("Suspended Thread acquired lock.");
                Thread.currentThread().suspend(); // Deprecated: doesn't release lock
                System.out.println("Suspended Thread resumed.");
            }
        }, "SuspendedThread");

        suspendedThread.start();
        Thread.sleep(100); // Give time for the thread to acquire lock and suspend
        System.out.println("Main thread attempting to acquire lock...");
        synchronized (lock) { // Problem line: main thread tries to acquire the same lock
            System.out.println("Main thread acquired lock.");
            suspendedThread.resume(); // This line might never be reached
        }
    }
}

Q922 easy code error

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

java

public class LoopError {
    public static void main(String[] args) {
        int a = 0;
        do (
            System.out.println(a);
            a++;
        ) while (a < 1);
    }
}

Q923 medium code error

What is the compilation error in the following code?

java

final class Vehicle {
    void honk() {
        System.out.println("Vehicle honks!");
    }
}

class Car extends Vehicle {
    void drive() {
        System.out.println("Car drives!");
    }
}

Q924 medium code output

What is the output of this code?

java

import java.io.BufferedReader;
import java.io.StringReader;
import java.io.IOException;

public class BufferedReaderTest {
    public static void main(String[] args) {
        String data = "ABCDEFG";
        try (BufferedReader br = new BufferedReader(new StringReader(data))) {
            System.out.print((char) br.read());
            br.skip(2);
            System.out.print((char) br.read());
            br.skip(Long.MAX_VALUE);
            System.out.print(br.readLine());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q925 easy code error

What will be the output or error when running this code?

java

class Car {
    String model;
    void start() {
        System.out.println(model + " starting.");
    }
}

public class Main {
    public static void main(String[] args) {
        Car myCar;
        myCar.start();
    }
}

Q926 hard code output

What is the output of this Java code?

java

String s1 = "Java";
String s2 = "Interview";
String s3 = "JavaInterview";
String s4 = s1 + s2;
String s5 = (s1 + s2).intern();

System.out.println(s3 == s4);
System.out.println(s3 == s5);

Q927 easy

Which method must a class implement when it implements the `Runnable` interface?

Q928 medium code error

What compilation error will occur in the `Child` class?

java

public class BaseException extends Exception {
    public BaseException(String msg) { super(msg); }
}

public class SpecificException extends BaseException {
    public SpecificException(String msg) { super(msg); }
}

class Parent {
    public void execute() throws SpecificException {
        System.out.println("Parent executing.");
    }
}

class Child extends Parent {
    @Override
    public void execute() throws BaseException {
        System.out.println("Child executing.");
    }
}

public class TestExceptions {
    public static void main(String[] args) {
        // Won't compile
    }
}

Q929 medium code error

What is the compile-time error in the following Java code?

java

class MyClass {
    int a;
    boolean b;

    public MyClass() {
        this(5); // Calls constructor with int
    }

    public MyClass(int a) {
        this(); // Calls no-arg constructor, creating a cycle
        this.a = a;
    }

    public static void main(String[] args) {
        new MyClass();
    }
}

Q930 medium code error

What error occurs when running this code, assuming '.' is the current directory?

java

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

public class MyClass {
    public static void main(String[] args) {
        File directory = new File("."); // Represents the current directory
        try (FileReader reader = new FileReader(directory)) {
            System.out.println("Reader created for directory.");
        } catch (IOException e) {
            System.err.println("Error: " + e.getMessage());
        }
    }
}

Q931 easy code error

What error will this Java code produce during compilation?

java

public class ArrayError {
    public static void main(String[] args) {
        int[][] matrix = int[2][3];
    }
}

Q932 medium code output

What does this Java code print?

java

import java.util.TreeSet;
import java.util.Set;

public class Test {
    public static void main(String[] args) {
        Set<String> words = new TreeSet<>();
        words.add("Banana");
        words.add("Apple");
        words.add("Cherry");
        words.add("apple");
        System.out.println(words);
    }
}

Q933 easy

What happens if you try to overload a method by only changing its access modifier (e.g., from `public` to `private`)?

Q934 medium

`java.io.FileReader` is a subclass of which abstract class, indicating it operates on character streams?

Q935 hard code output

What is the output of this code?

java

public class Test {
    public static void main(String[] args) {
        String result = "";
        outer: for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (i == 1 && j == 1) {
                    continue outer;
                }
                result += "(" + i + "," + j + ")";
            }
        }
        System.out.print(result);
    }
}

Q936 medium

When is an explicit type cast NOT required for object references in Java?

Q937 hard code output

What is the output of this code?

java

public class DataTypeChallenge {
    public static void main(String[] args) {
        Integer a = 127;
        Integer b = 127;
        Integer c = 128;
        Integer d = 128;
        System.out.println(a == b);
        System.out.println(c == d);
    }
}

Q938 easy code output

What is the output of this Java code snippet?

java

import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
        TreeMap<Integer, String> treeMap = new TreeMap<>();
        treeMap.put(1, "One");
        treeMap.remove(1);
        System.out.println(treeMap.isEmpty());
    }
}

Q939 medium

What is the average time complexity for the `put`, `get`, and `remove` operations in a `TreeMap`?

Q940 medium

Which characteristic primarily differentiates `Runnable` from `Callable`?

☕ Java MCQ Questions – Page 47