Java MCQ Questions – Page 170 of 200

Q: What will be the result of compiling and running this Java code?

A) Compile-time error: Illegal forward reference to VALUE.. The `VALUE` field is declared `final` and initialized in the static block by calling `computeValue()`. However, `computeValue()` attempts to read `VALUE` before it has been definitely assigned, leading to a compile-time error known as an 'illegal forward reference'.

Q: What does this Java code print to the console?

A) 0 1 3 4. The 'continue' statement skips the rest of the current iteration when i is 2 and proceeds to the next iteration of the loop. Thus, 2 is not printed, but the loop continues for other values.

Q: For a `TreeMap` to work correctly using the natural ordering of its keys, what essential characteristic must the key objects possess?

C) They must implement the `Comparable` interface.. To use natural ordering, `TreeMap` requires that its keys implement the `Comparable` interface, allowing `TreeMap` to compare keys and maintain their sorted order. If a custom `Comparator` is provided, this requirement for keys is relaxed.

Q: What is the output of this code?

C) Either 'A B ' or 'B A '. Each `Item` object has its own intrinsic lock. Since `t1` and `t2` are calling synchronized methods on *different* objects (`itemA` and `itemB`), their executions are not mutually exclusive. They can run concurrently, and the print order depends on thread scheduling.

Q: What does this Java code print?

A) 6. Both `intToString.apply(100)` and `integerToString.apply(200)` convert the respective numbers to string representations "100" and "200". Each string has a length of 3. The sum of their lengths is 3 + 3 = 6.

Q: What is the content of 'new_file.txt' after this code executes, assuming 'new_file.txt' does not exist initially?

C) Content for a new file.. If the file specified in the FileWriter constructor does not exist, FileWriter will attempt to create it. Upon successful writing and closing (via try-with-resources), the file will contain the written content.

Q: What is the approximate default buffer size (in characters/bytes) used by `BufferedReader` if not specified in its constructor?

D) 8192 bytes. The default buffer size for `BufferedReader` (and many other buffered I/O classes in Java) is commonly 8192 bytes (8KB), which is a good balance for general-purpose I/O.

Q: What is the output of this code?

A) [10, 40]. First, `numbers.remove(new Integer(20))` calls `remove(Object o)`, removing the element `20`. The list becomes `[10, 30, 40]`. Then, `numbers.remove(1)` calls `remove(int index)`, removing the element at index 1 (which is `30`). The final list is `[10, 40]`.

Q: What will happen when this Java code is compiled and executed?

A) Compilation Error. The `process()` method catches an `IOException` and then re-throws it. Since `IOException` is a checked exception, the method must either handle it (which it does not for the re-throw) or declare it in its `throws` clause. As it doesn't, it results in a compilation error.

Q: What is the error in this Java code snippet?

A) Compile-time error: incompatible types: StringBuilder cannot be converted to String. A `StringBuilder` object cannot be directly assigned to a `String` reference. They are distinct types, and there is no implicit conversion. The `StringBuilder.toString()` method must be explicitly called to convert it to a `String`, resulting in a compile-time error.

Q3381 hard code error

What will be the result of compiling and running this Java code?

java

public class MyClass {
    private static final int VALUE;
    static {
        System.out.println("Static init block");
        VALUE = computeValue();
    }
    private static int computeValue() {
        return VALUE + 1; 
    }
    public static void main(String[] args) {
        System.out.println(MyClass.VALUE);
    }
}

Q3382 easy code output

What does this Java code print to the console?

java

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            if (i == 2) {
                continue;
            }
            System.out.print(i + " ");
        }
    }
}

Q3383 medium

For a `TreeMap` to work correctly using the natural ordering of its keys, what essential characteristic must the key objects possess?

Q3384 easy code output

What is the output of this code?

java

class Item {
    private String name;
    public Item(String name) { this.name = name; }
    public synchronized void process() {
        System.out.print(name + " ");
    }
}

public class MyProgram {
    public static void main(String[] args) throws InterruptedException {
        Item itemA = new Item("A");
        Item itemB = new Item("B");
        Thread t1 = new Thread(() -> itemA.process());
        Thread t2 = new Thread(() -> itemB.process());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }
}

Q3385 medium code output

What does this Java code print?

java

import java.util.function.IntFunction;
import java.util.function.Function;

public class Test {
    public static void main(String[] args) {
        IntFunction<String> intToString = String::valueOf;
        Function<Integer, String> integerToString = String::valueOf;

        String result1 = intToString.apply(100);
        String result2 = integerToString.apply(200);

        System.out.println(result1.length() + result2.length());
    }
}

Q3386 medium code output

What is the content of 'new_file.txt' after this code executes, assuming 'new_file.txt' does not exist initially?

java

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

public class FileCreationTest {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("new_file.txt")) {
            writer.write("Content for a new file.");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Q3387 medium

What is the approximate default buffer size (in characters/bytes) used by `BufferedReader` if not specified in its constructor?

Q3388 hard code output

What is the output of this code?

java

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(10); 
        numbers.add(20); 
        numbers.add(30); 
        numbers.add(40); 

        numbers.remove(new Integer(20)); 
        numbers.remove(1); 

        System.out.println(numbers);
    }
}

Q3389 easy code error

What will happen when this Java code is compiled and executed?

java

class MyClass {
    public void process() {
        try {
            throw new java.io.IOException("Issue");
        } catch (java.io.IOException e) {
            throw e; 
        }
    }
}

Q3390 hard code error

What is the error in this Java code snippet?

java

public class BuilderError {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Mutable");
        String s = sb;
        System.out.println(s);
    }
}

Q3391 easy code output

What does this code print to the console?

java

public class Main {
    public static void main(String[] args) {
        int p = 7;
        p += 3;
        System.out.println(p);
    }
}

Q3392 easy code error

What is the expected error when compiling and running the following Java code?

java

import java.util.LinkedList;

public class MyClass {
    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<>();
        list.add("A");
        list.add("B");
        for (String s : list) {
            if (s.equals("A")) {
                list.add("C"); // Modifying list while iterating with a for-each loop
            }
        }
    }
}

Q3393 hard code error

What is the runtime error encountered when executing this Java code snippet?

java

import java.util.HashSet;
import java.util.Iterator;

public class Main {
    public static void main(String[] args) {
        HashSet<String> set = new HashSet<>();
        set.add("A");
        set.add("B");
        Iterator<String> iterator = set.iterator();
        while (iterator.hasNext()) {
            String element = iterator.next();
            if (element.equals("A")) {
                set.remove(element);
            }
        }
    }
}

Q3394 hard

What is the primary architectural purpose of the `ThreadGroup` class in Java?

Q3395 easy code error

What is the output or error of the following Java code?

java

public class ExceptionTest {
    public static void main(String[] args) {
        try {
            System.out.println("Inside try block");
        }
    }
}

Q3396 hard

You have a `TreeMap<Integer, String> map` containing `{1="A", 5="E", 10="J"}`. You create a `NavigableMap<Integer, String> sub = map.subMap(1, true, 5, true);`. If you then call `sub.remove(1);`, what will be the state of the original `map`?

Q3397 hard

Given the following Java code structure (without curly braces): `if (condition1) if (condition2) statementA; else statementB;`. To which `if` statement does `else statementB;` logically belong according to Java's rules?

Q3398 hard code error

What compile-time error will this Java code produce?

java

public class OperatorError3 {
    public static void main(String[] args) {
        int x = 5;
        double y = 10.0;
        int result = (x > y) ? x : "Hello"; // Error line
        System.out.println(result);
    }
}

Q3399 easy code error

What compilation error will occur when compiling this Java code?

java

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

public class MyClass {
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(System.in);
        try {
            String line = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Q3400 medium code output

What is the outcome of running this code?

java

public class Main {
    private static Object lock1 = new Object();
    private static Object lock2 = new Object();

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> {
            synchronized (lock1) {
                System.out.println("Thread 1: Holding lock 1...");
                try { Thread.sleep(100); } catch (InterruptedException e) {}
                synchronized (lock2) {
                    System.out.println("Thread 1: Holding lock 1 & 2");
                }
            }
        });

        Thread t2 = new Thread(() -> {
            synchronized (lock2) {
                System.out.println("Thread 2: Holding lock 2...");
                try { Thread.sleep(100); } catch (InterruptedException e) {}
                synchronized (lock1) {
                    System.out.println("Thread 2: Holding lock 1 & 2");
                }
            }
        });

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

☕ Java MCQ Questions – Page 170