Java MCQ Questions – Page 114 of 200

Q: What error will occur when compiling and running the provided Java code?

A) Compile-time error: 'age' has private access in 'Person'. The 'age' field is declared as private within the 'Person' class, preventing direct modification from external classes like 'Main'. This is a core principle of encapsulation.

Q: What is the output of this code?

C) Waiting...In progress. (End). Due to fall-through, when `status` is `PENDING`, the code inside `case PENDING` executes, then without a `break`, execution continues into `case PROCESSING`. The `break` in `case PROCESSING` then exits the `switch` statement.

Q: What error occurs when compiling this Java code?

A) Compilation error: Unhandled exception type java.io.IOException. The `readFile` method throws a checked exception (`IOException`) but neither handles it with a try-catch block nor declares it in its signature using `throws IOException`. This results in a compile-time error.

Q: What exception will be thrown when executing this Java code snippet?

A) NoSuchElementException. The `remove()` method of the `Queue` interface (implemented by `LinkedList`) throws a `NoSuchElementException` if the queue is empty. In contrast, `poll()` would return `null`.

Q: Consider a scenario where a variable is declared exclusively within the `do` block of a `do-while` loop. If this variable is then referenced in the `while` condition, what is the outcome?

A) The code will result in a compile-time error due to the variable being out of scope in the `while` condition.. Variables declared within a block (like the `do` block) are local to that block. They cease to exist once the block's execution completes, making them inaccessible to the `while` condition which is outside the `do` block's scope.

Q: What does this code print?

A) Processing started. Executing specific task.. The anonymous inner class provides the implementation for `doProcess()`. The `process()` method then calls `doProcess()`, leading to the execution of both print statements in the specified order.

Q: What is the output of this code?

A) Caught error: Stream closed Final content: Initial data.. Calling `writer.close()` flushes the buffer and closes the stream. Any subsequent `write()` operation on a closed stream will throw an `IOException` (typically 'Stream closed'). The `StringWriter` will retain the data written before the close.

Q: A developer iterates over a `LinkedList` using its `iterator()` and simultaneously modifies the list's structure (e.g., by calling `list.add()` or `list.remove()`) outside the iterator's own `remove()` method. What is the most likely outcome?

C) A `ConcurrentModificationException` will be thrown on the next call to `iterator.next()` or `iterator.hasNext()`, as `LinkedList` iterators are fail-fast.. LinkedList's iterators are fail-fast. If the list is structurally modified (e.g., elements added or removed directly via the list's methods) while an iteration is in progress, the iterator will detect this and throw a `ConcurrentModificationException`.

Q: What is the output of this Java code?

A) Constructor called!. When `new MyClass()` is executed, the constructor of `MyClass` is invoked, which prints 'Constructor called!' to the console.

Q: What compile-time error will occur in the `main` method?

A) error: AbstractCustomException is abstract; cannot be instantiated. An `abstract` class cannot be directly instantiated using the `new` keyword. You can only create instances of concrete subclasses of an abstract class.

Q2261 easy code error

What error will occur when compiling and running the provided Java code?

java

class Person {
    private int age;
}

public class Main {
    public static void main(String[] args) {
        Person p = new Person();
        p.age = 30;
    }
}

Q2262 hard code output

What is the output of this code?

java

public class SwitchTest {
    enum Status { PENDING, PROCESSING, COMPLETED }
    public static void main(String[] args) {
        Status status = Status.PENDING;
        String desc = "";
        switch (status) {
            case PENDING:
                desc += "Waiting...";
            case PROCESSING:
                desc += "In progress.";
                break;
            case COMPLETED:
                desc += "Done!";
                break;
            default:
                desc += "Unknown.";
        }
        System.out.println(desc + " (End)");
    }
}

Q2263 medium code error

What error occurs when compiling this Java code?

java

import java.io.IOException;

public class ExceptionHandling {
    public static void readFile() {
        // Simulate an operation that might throw IOException
        throw new IOException("File not found");
    }

    public static void main(String[] args) {
        // Main method calls readFile
    }
}

Q2264 medium code error

What exception will be thrown when executing this Java code snippet?

java

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

public class QueueError {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        queue.remove(); // Attempt to remove from an empty queue
    }
}

Q2265 hard

Consider a scenario where a variable is declared exclusively within the `do` block of a `do-while` loop. If this variable is then referenced in the `while` condition, what is the outcome?

Q2266 hard code output

What does this code print?

java

abstract class AbstractProcessor {
    public void process() {
        System.out.println("Processing started.");
        doProcess();
    }
    protected abstract void doProcess();
}

public class Main {
    public static void main(String[] args) {
        AbstractProcessor processor = new AbstractProcessor() {
            @Override
            protected void doProcess() {
                System.out.println("Executing specific task.");
            }
        };
        processor.process();
    }
}

Q2267 easy code output

What is the output of this code?

java

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

public class Main {
    public static void main(String[] args) {
        StringWriter stringWriter = new StringWriter();
        try (BufferedWriter writer = new BufferedWriter(stringWriter)) {
            writer.write("Initial data.");
            writer.close(); // Explicitly closing the writer
            writer.write("Attempt to write after close.");
        } catch (IOException e) {
            System.out.println("Caught error: " + e.getMessage());
        }
        System.out.print("Final content: " + stringWriter.toString());
    }
}

Q2268 hard

A developer iterates over a `LinkedList` using its `iterator()` and simultaneously modifies the list's structure (e.g., by calling `list.add()` or `list.remove()`) outside the iterator's own `remove()` method. What is the most likely outcome?

Q2269 easy code output

What is the output of this Java code?

java

class MyClass {
    MyClass() {
        System.out.println("Constructor called!");
    }
}
public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
    }
}

Q2270 easy code error

What compile-time error will occur in the `main` method?

java

abstract class AbstractCustomException extends Exception {
    public AbstractCustomException(String message) { super(message); }
}

public class Main {
    public static void main(String[] args) {
        try {
            throw new AbstractCustomException("Cannot instantiate"); 
        } catch (AbstractCustomException e) {
            System.out.println(e.getMessage());
        }
    }
}

Q2271 easy

Which of the following wrapper classes is NOT traditionally supported as an expression in a standard Java `switch` statement?

Q2272 hard

How do non-static inner classes impact the encapsulation of their outer class?

Q2273 hard code output

What is the output of this code?

java

class Parent {
    protected void printInfo() {
        System.out.println("Parent Info");
    }
}

class Child extends Parent {
    @Override
    void printInfo() {
        System.out.println("Child Info");
    }
}

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

Q2274 hard code error

What is the error encountered when running this Java code?

java

public class ArrayCopyError {
    public static void main(String[] args) {
        int[] source = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int[] dest = source;
        System.arraycopy(source, 5, dest, 0, 8);
    }
}

Q2275 hard code output

What is the output of this code?

java

class Overload {
    Overload(Object o) { System.out.print("Object "); }
    Overload(String s) { System.out.print("String "); }
    Overload(Integer i) { System.out.print("Integer "); }
    Overload(Number n) { System.out.print("Number "); }
}
public class Main {
    public static void main(String[] args) {
        new Overload(null);
        new Overload(5);
        new Overload("hello");
    }
}

Q2276 easy code output

What is the output of this code?

java

public class Main {
    public static String testMethod() {
        try {
            System.out.print("Try ");
            return "Return from try";
        } finally {
            System.out.print("Finally ");
        }
    }
    public static void main(String[] args) {
        System.out.println(testMethod());
    }
}

Q2277 hard code error

What exception is thrown when the `oos.writeObject(child)` line is executed in the `main` method?

java

import java.io.*;

class NonSerializableParent {
    private String parentData;
    public NonSerializableParent(String parentData) { this.parentData = parentData; }
    public String getParentData() { return parentData; }
}

class SerializableChild extends NonSerializableParent implements Serializable {
    private static final long serialVersionUID = 1L;
    private String childData;
    public SerializableChild(String parentData, String childData) {
        super(parentData);
        this.childData = childData;
    }
    public String getChildData() { return childData; }
}

public class SerializationError2 {
    public static void main(String[] args) throws IOException {
        SerializableChild child = new SerializableChild("Parent", "Child");
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(child); // Error occurs here
        oos.close();
    }
}

Q2278 medium code error

What is the error in this Java code related to method overloading?

java

public class OverloadChecker {
    public void printValue(int a) {
        System.out.println("Int: " + a);
    }

    public int printValue(int a) { // This line causes the error
        return a;
    }

    public static void main(String[] args) {
        OverloadChecker oc = new OverloadChecker();
        oc.printValue(10);
    }
}

Q2279 easy code output

What does this code print?

java

public class MyClass {
    public static void callerMethod() {
        try {
            System.out.println("Caller: In try");
            throw new IllegalStateException("State issue");
        } catch (IllegalStateException e) {
            System.out.println("Caller: Caught " + e.getMessage());
        }
    }

    public static void main(String[] args) {
        System.out.println("Main: Before call");
        callerMethod();
        System.out.println("Main: After call");
    }
}

Q2280 easy

When creating a `FileReader` object, which specific Java class instance can be passed to its constructor, besides a `String` path?

☕ Java MCQ Questions – Page 114