Java MCQ Questions – Page 182 of 200

Q: What does this code print?

A) Task started Caught NPE: Simulated NPE. The `executeTask` method throws a `NullPointerException` (a subclass of `RuntimeException`). The `main` method catches this specific exception first, so the `NullPointerException` catch block is executed.

Q: What is the output of this Java code?

A) myFile.txt. The `getName()` method returns the name of the file or directory denoted by this abstract pathname. For 'path/to/myFile.txt', it returns 'myFile.txt'.

Q: What is the result of compiling the following Java code, assuming 'somefile.txt' may or may not exist?

C) A compile-time error: unhandled exception type IOException.. The constructor `new FileReader("somefile.txt")` can throw a `FileNotFoundException` (which is an `IOException`). Since this is a checked exception and it's not handled in a `try-catch` block or declared in the `main` method's `throws` clause, it will result in a compile-time error.

Q: When a `break` statement is encountered inside a Java `for` loop, what is its immediate effect?

B) It terminates the innermost loop immediately and transfers control to the statement following the loop. The `break` statement is used to terminate the loop (for, while, do-while) or switch statement immediately, transferring control to the statement directly after the terminated construct.

Q: What is the compile-time error in this Java program?

A) Compile-time error: label 'unknownLabel' not found. A labeled `break` statement must refer to an enclosing labeled statement. In this case, 'unknownLabel' is not defined as an enclosing label for a loop or switch, resulting in a compile-time error.

Q: What compile-time error will occur when compiling this Java code?

B) Compile-time error: Incompatible types. Found: 'double', Required: 'char, byte, short, int, Character, Byte, Short, Integer, String, or an enum'. The 'switch' statement in Java does not support 'double' as a controlling expression type. It only accepts char, byte, short, int, their wrapper types, String, or enums.

Q: What does this code print?

A) London. The `get(index)` method retrieves the element at the specified position. In Java, list indices are 0-based, so `get(0)` returns the first element, which is "London".

Q: What does this code print?

B) 1. The `final` keyword applied to a reference variable (`names`) means that the reference itself cannot be reassigned to point to a different object. It does *not* make the object it refers to immutable. Since `ArrayList` is a mutable object, its contents can be modified. The code adds "Alice", then removes it, then adds "Bob". The final size of the list is 1.

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

A) true true false. For 4: (true && true) || true = true. For -2: (false && false) || true = true. For 11: (false && true) || false = false.

Q: What is the output of this code?

B) 2. The `equals` method considers items equal if their `id` is the same (e.g., (1, 'Apple') equals (1, 'Orange')). However, the `hashCode` method only uses the `name`, which is different for 'Apple' and 'Orange'. This violates the `hashCode`/`equals` contract, causing `HashSet` to place these logically equal objects into different hash buckets, thus storing both.

Q3621 medium code output

What does this code print?

java

class MyExecutor {
    static void executeTask() throws RuntimeException {
        System.out.println("Task started");
        throw new NullPointerException("Simulated NPE");
    }

    public static void main(String[] args) {
        try {
            executeTask();
        } catch (NullPointerException e) {
            System.out.println("Caught NPE: " + e.getMessage());
        } catch (RuntimeException e) {
            System.out.println("Caught RuntimeException: " + e.getMessage());
        }
    }
}

Q3622 easy code output

What is the output of this Java code?

java

import java.io.File;

public class FileTest {
    public static void main(String[] args) {
        File file = new File("path/to/myFile.txt");
        System.out.println(file.getName());
    }
}

Q3623 medium code error

What is the result of compiling the following Java code, assuming 'somefile.txt' may or may not exist?

java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class TestClass {
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new FileReader("somefile.txt"));
        System.out.println("File opened.");
        try {
            br.close();
        } catch (IOException e) {
            // Handle close exception
        }
    }
}

Q3624 medium

When a `break` statement is encountered inside a Java `for` loop, what is its immediate effect?

Q3625 medium code error

What is the compile-time error in this Java program?

java

public class Test {
    public static void main(String[] args) {
        outerLoop: for (int i = 0; i < 3; i++) {
            innerLoop: for (int j = 0; j < 3; j++) {
                if (i * j == 4) {
                    break unknownLabel;
                }
            }
        }
    }
}

Q3626 easy code error

What compile-time error will occur when compiling this Java code?

java

public class MyClass {
    public static void main(String[] args) {
        double value = 3.14;
        switch (value) {
            case 3.14:
                System.out.println("PI");
                break;
            default:
                System.out.println("Other value");
        }
    }
}

Q3627 easy code output

What does this code print?

java

import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<String> cities = new LinkedList<>();
        cities.add("London");
        cities.add("Paris");
        cities.add("Rome");
        System.out.println(cities.get(0));
    }
}

Q3628 hard code output

What does this code print?

java

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

public class Main {
    public static void main(String[] args) {
        final List<String> names = new ArrayList<>();
        names.add("Alice");
        names.remove(0);
        names.add("Bob");
        System.out.println(names.size());
    }
}

Q3629 medium code output

What is the output of this Java code snippet?

java

import java.util.function.Predicate;

public class Test {
    public static void main(String[] args) {
        Predicate<Integer> isEven = num -> num % 2 == 0;
        Predicate<Integer> isPositive = num -> num > 0;
        Predicate<Integer> isLessThanTen = num -> num < 10;

        Predicate<Integer> combined = isEven.and(isPositive).or(isLessThanTen);

        System.out.println(combined.test(4));
        System.out.println(combined.test(-2));
        System.out.println(combined.test(11));
    }
}

Q3630 hard code output

What is the output of this code?

java

import java.util.HashSet;
import java.util.Objects;

class ItemA {
    int id;
    String name;
    public ItemA(int id, String name) { this.id = id; this.name = name; }
    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ItemA itemA = (ItemA) o;
        return id == itemA.id; // Only compares id
    }
    @Override public int hashCode() { return Objects.hash(name); } // Only hashes name
}

public class Main {
    public static void main(String[] args) {
        HashSet<ItemA> set = new HashSet<>();
        set.add(new ItemA(1, "Apple"));
        set.add(new ItemA(1, "Orange"));
        System.out.println(set.size());
    }
}

Q3631 medium code error

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

java

import java.util.TreeSet;
import java.util.SortedSet;

public class Main {
    public static void main(String[] args) {
        TreeSet<Integer> originalSet = new TreeSet<>();
        originalSet.add(10);
        originalSet.add(20);
        originalSet.add(30);

        SortedSet<Integer> sub = originalSet.subSet(25, 15);
        System.out.println(sub.size());
    }
}

Q3632 medium

In Java, when are nested `if` statements typically most appropriate?

Q3633 easy

Functional interfaces are primarily designed to be target types for which Java 8 feature?

Q3634 hard code error

What is the result of compiling and running the following Java code snippet?

java

import java.util.List;

public class StringError {
    public static void main(String[] args) {
        List<Integer> numbers = List.of(1, 2, 3);
        String result = String.join("-", numbers);
        System.out.println(result);
    }
}

Q3635 hard code error

What is the output of this code?

java

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

public class FilterRuntimeException {
    public static void main(String[] args) {
        File dir = new File("."); // Current directory
        FilenameFilter brokenFilter = (currentDir, name) -> {
            if (name.contains("error")) {
                throw new RuntimeException("Filter processing failed for: " + name);
            }
            return true;
        };

        try {
            File errorFile = new File(dir, "file_with_error_in_name.txt");
            errorFile.createNewFile();

            String[] files = dir.list(brokenFilter); // This call will trigger the filter
            System.out.println("Files listed: " + (files != null ? files.length : "null"));
            
            errorFile.delete();
        } catch (RuntimeException e) {
            System.out.println("Caught RuntimeException: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("Caught IOException: " + e.getClass().getSimpleName());
        }
    }
}

Q3636 hard code output

Consider this Java code. What is the output?

java

public class ThreadLocalRunnable {
    private static ThreadLocal<String> threadLocalVar = ThreadLocal.withInitial(() -> "Default");

    public static void main(String[] args) throws InterruptedException {
        Runnable task = () -> {
            System.out.println(Thread.currentThread().getName() + " Initial: " + threadLocalVar.get());
            threadLocalVar.set(Thread.currentThread().getName() + " Value");
            try { Thread.sleep(50); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
            System.out.println(Thread.currentThread().getName() + " Final: " + threadLocalVar.get());
        };

        Thread t1 = new Thread(task, "Thread-1");
        Thread t2 = new Thread(task, "Thread-2");

        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }
}

Q3637 medium code output

What does the following Java code print to the console?

java

import java.util.HashSet;
import java.util.Set;

class MutableItem {
    private int value;
    public MutableItem(int value) { this.value = value; }
    public void setValue(int value) { this.value = value; }
    @Override public int hashCode() { return value; }
    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MutableItem that = (MutableItem) o;
        return value == that.value;
    }
}

public class Main {
    public static void main(String[] args) {
        Set<MutableItem> items = new HashSet<>();
        MutableItem item1 = new MutableItem(10);
        items.add(item1);
        item1.setValue(20); 
        System.out.println(items.contains(item1));
    }
}

Q3638 hard code output

What is the output of this code?

java

import java.io.*;

public class Test {
    public static void main(String[] args) throws IOException {
        String data = "ABC\r\nDEF\nGH\rI";
        BufferedReader br = new BufferedReader(new StringReader(data));
        System.out.println(br.readLine());
        System.out.println(br.readLine());
        System.out.println(br.readLine());
        System.out.println(br.readLine());
        br.close();
    }
}

Q3639 easy

In Java polymorphism, can a reference variable of a superclass type hold an object of its subclass?

Q3640 medium code output

What does this code print?

java

import java.util.TreeMap;
import java.util.Map;

public class TreeMapNullValue {
    public static void main(String[] args) {
        TreeMap<String, String> map = new TreeMap<>();
        map.put("one", "1");
        map.put("two", null);
        map.put("three", "3");
        System.out.println(map.containsKey("two") + "," + map.containsValue(null));
    }
}

☕ Java MCQ Questions – Page 182