Java MCQ Questions – Page 101 of 200

Q: What kind of error will occur when this Java code is executed?

C) Compilation Error: no suitable constructor found for StringBuilder(char[]). The `StringBuilder` class does not have a constructor that directly accepts a `char[]`. You would typically convert the `char[]` to a `String` first, e.g., `new StringBuilder(new String(chars))`.

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

B) Compilation Error: `display()` in `Sub` cannot override `display()` in `Super`; overridden method is final.. A method declared as `final` cannot be overridden by subclasses. Attempting to do so results in a compile-time error.

Q: When you perform an operation like `str.concat("suffix")` on a String `str`, what is the outcome?

B) A new String object is created with the concatenated content.. Due to String immutability, `concat()` and similar methods always return a new String object containing the result, rather than modifying the original.

Q: What is wrong with this Java code?

B) The `Supplier ` expects a `String` return type, but the lambda returns an `int`.. The `Supplier ` interface expects its `get()` method to return a `String`. The lambda expression `() -> 123` returns an `int`, leading to a type mismatch error during compilation.

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

A) Apple,Banana,. The enhanced `for` loop iterates through each element in the `fruits` array. Each `fruit` is printed followed by a comma, all on the same line.

Q: Which `StringBuffer` method is used to append the string representation of an argument to the sequence?

A) `append()`. The `append()` method is specifically designed in `StringBuffer` (and `StringBuilder`) to add new characters or string representations to the end of the existing sequence.

Q: What is the output of this code?

B) catcat1. A `PriorityQueue` allows duplicate elements. With natural string ordering, 'cat' comes before 'dog'. So, 'cat' is polled first, then the other 'cat' is polled. Finally, 'dog' remains, making the size 1.

Q: What is the most significant difference when choosing between `String.replace(CharSequence target, CharSequence replacement)` and `String.replaceAll(String regex, String replacement)` for replacing all occurrences of a literal substring?

A) `replace()` offers better performance as it treats arguments as literals, avoiding the regex engine overhead.. `String.replace(CharSequence, CharSequence)` treats its arguments as literal sequences and does not use a regular expression engine, making it more performant for simple literal replacements than `replaceAll()`, which always interprets its first argument as a regular expression.

Q: What is the output of this Java code?

A) Red Blue. Each object (car1 and car2) holds its own independent copy of the 'color' instance variable, initialized by its respective constructor call.

Q: What is the output of this Java code?

C) 32 0 1. `compareTo()` performs lexicographical comparison based on Unicode values. 'a' has a higher Unicode value than 'A', so `s1.compareTo(s2)` is positive (32). `compareToIgnoreCase()` ignores case, so `apple` and `Apple` are considered equal (0 difference). 'banana' comes after 'apple', so `s3.compareTo(s1)` yields a positive value (e.g., 1).

Q2001 easy code error

What kind of error will occur when this Java code is executed?

java

public class Test {
    public static void main(String[] args) {
        char[] chars = {'J', 'a', 'v', 'a'};
        StringBuilder sb = new StringBuilder(chars);
        System.out.println(sb);
    }
}

Q2002 hard code error

What is the error in the following Java code?

java

class Super {
    final void display() {
        System.out.println("Super display");
    }
}

class Sub extends Super {
    void display() { // Attempting to override final method
        System.out.println("Sub display");
    }
}

Q2003 easy

When you perform an operation like `str.concat("suffix")` on a String `str`, what is the outcome?

Q2004 easy code error

What is wrong with this Java code?

java

import java.util.function.Supplier;

public class Test {
    public static void main(String[] args) {
        Supplier<String> supplier = () -> 123;
    }
}

Q2005 easy code output

What is the output of this Java code snippet?

java

public class ArrayTest {
    public static void main(String[] args) {
        String[] fruits = {"Apple", "Banana"};
        for (String fruit : fruits) {
            System.out.print(fruit + ",");
        }
    }
}

Q2006 medium

Which `StringBuffer` method is used to append the string representation of an argument to the sequence?

Q2007 medium code output

What is the output of this code?

java

import java.util.PriorityQueue;
import java.util.Queue;

public class PriorityQueueDuplicates {
    public static void main(String[] args) {
        Queue<String> pq = new PriorityQueue<>();
        pq.offer("cat");
        pq.offer("dog");
        pq.offer("cat");
        System.out.print(pq.poll());
        System.out.print(pq.poll());
        System.out.print(pq.size());
    }
}

Q2008 hard

What is the most significant difference when choosing between `String.replace(CharSequence target, CharSequence replacement)` and `String.replaceAll(String regex, String replacement)` for replacing all occurrences of a literal substring?

Q2009 medium code output

What is the output of this Java code?

java

class Car {
    String color;
    Car(String c) {
        this.color = c;
    }
}
public class Main {
    public static void main(String[] args) {
        Car car1 = new Car("Red");
        Car car2 = new Car("Blue");
        System.out.println(car1.color + " " + car2.color);
    }
}

Q2010 hard code output

What is the output of this Java code?

java

String s1 = "apple";
String s2 = "Apple";
String s3 = "banana";

System.out.println(s1.compareTo(s2));
System.out.println(s1.compareToIgnoreCase(s2));
System.out.println(s3.compareTo(s1));

Q2011 medium code output

What is the output of this code?

java

import java.util.HashMap;

class MyKey {
    int id;
    public MyKey(int id) { this.id = id; }
}

public class Test {
    public static void main(String[] args) {
        HashMap<MyKey, String> map = new HashMap<>();
        MyKey k1 = new MyKey(1);
        MyKey k2 = new MyKey(1); // Different object, same 'id'
        map.put(k1, "First Value");
        System.out.println(map.get(k2));
    }
}

Q2012 hard code error

What compile-time error occurs when attempting to compile this Java code?

java

final class Immutable {
    public String name;
    public Immutable(String name) {
        this.name = name;
    }
}

class SubImmutable extends Immutable {
    public SubImmutable(String name) {
        super(name);
    }
}

Q2013 easy

Which method is used to add an element to the tail of a Queue and throws an exception if the operation fails (e.g., if the queue is full)?

Q2014 medium code error

What error occurs when compiling this Java code?

java

public class LoopTest {
    public static void main(String[] args) {
        int data;
        do {
            System.out.println("Processing...");
        } while (data < 10);
    }
}

Q2015 hard code error

What runtime error will this Java code snippet throw?

java

public class Test {
    public static void main(String[] args) {
        Object[][] matrix = new String[2][2];
        matrix[0][0] = "Java";
        matrix[1][0] = new Integer(100);
        System.out.println(matrix[1][0]);
    }
}

Q2016 hard code error

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

java

import java.util.function.Function;

class Processor {
    public String process(Integer i) {
        return "Processed: " + i;
    }
}

public class Main {
    public static void main(String[] args) {
        Function<Integer, String> func = Processor::process;
        System.out.println(func.apply(10));
    }
}

Q2017 medium code output

What is the output of this code?

java

public class StringBufferTest {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        sb.append("Hello");
        sb.ensureCapacity(30);
        sb.append("World");
        System.out.print(sb.capacity() + " " + sb.length());
    }
}

Q2018 hard code output

What is the output of this code?

java

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

class AlwaysTrueEqualsItem {
    int id;
    public AlwaysTrueEqualsItem(int id) { this.id = id; }
    @Override public boolean equals(Object o) { return true; } // Always returns true
    @Override public int hashCode() { return Objects.hash(id); }
}

public class Main {
    public static void main(String[] args) {
        HashSet<AlwaysTrueEqualsItem> set = new HashSet<>();
        set.add(new AlwaysTrueEqualsItem(1));
        set.add(new AlwaysTrueEqualsItem(2));
        System.out.println(set.size());
    }
}

Q2019 medium code error

What is the output of this Java code?

java

public class ExceptionFlow4 {
    public static void main(String[] args) {
        System.out.println(testMethod());
    }

    public static String testMethod() {
        try {
            System.out.println("Try block");
            throw new RuntimeException("Test exception");
        } catch (RuntimeException e) {
            System.out.println("Catch block");
            return "Returned from catch";
        } finally {
            System.out.println("Finally block");
        }
    }
}

Q2020 medium code error

Consider the following Java code. What will be the compilation error?

java

public class UninitializedVariable {
    public static void main(String[] args) {
        int x;
        int y = x + 10;
        System.out.println(y);
    }
}

☕ Java MCQ Questions – Page 101