Java MCQ Questions – Page 58 of 200

Q: In a complex `if` condition like `if (a > 10 && b < 5 || c == 0)`, which logical operator has the lowest precedence and therefore is evaluated last?

D) `||`. In Java, comparison operators (`>`, `<`, `==`) have higher precedence than logical operators. Among logical operators, `&&` (logical AND) has higher precedence than `||` (logical OR). Thus, `||` is evaluated last.

Q: What kind of error will occur when executing the following Java code?

A) java.lang.IllegalStateException. For bounded queues like ArrayBlockingQueue, the `add()` method throws an IllegalStateException if the queue is full. The `offer()` method, in contrast, would return `false` without throwing an exception.

Q: Given `byte b1 = 100; byte b2 = 50;`, which of the following expressions will compile without error and produce an `int` result equal to `150`?

A) `int result = b1 + b2;`. Arithmetic operations on `byte` or `short` operands in Java automatically promote them to `int` before calculation. Therefore, `b1 + b2` results in an `int` value of `150`. Options B and C require explicit casting back to `byte` (and B won't compile without it), while D involves an unnecessary cast that might lead to truncation for larger values.

Q: In a class hierarchy, what is the correct order of constructor execution when an object of a subclass is created?

B) Superclass constructor first, then subclass constructor.. When a subclass constructor is invoked, it implicitly or explicitly calls a superclass constructor, and this chain continues up to `Object`'s constructor. Thus, superclass constructors execute before subclass constructors.

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

B) Error: Method does not override or implement a method from a supertype. Private methods are not inherited by subclasses, so they cannot be overridden. The `@Override` annotation correctly indicates a compilation error because 'confidentialMethod' in 'Child' is a new method, not an override.

Q: What is the output of this code?

B) 2. All objects will hash to the same bucket (0). `HashSet` will then rely on the `equals()` method to determine uniqueness. `ZeroHashItem(10)` and `ZeroHashItem(20)` are distinct by `equals()`, so both are added. The second `ZeroHashItem(10)` is a duplicate of the first, so it's not added. Performance is poor due to many collisions, but correctness is maintained.

Q: If an exception occurs in the `try` block and there is no matching `catch` block to handle it, what happens regarding the `finally` block?

B) The `finally` block executes, and then the exception is propagated up the call stack.. Even if an exception is not caught, the `finally` block will execute before the uncaught exception propagates further up the call stack, potentially terminating the thread.

Q: What does this code print?

A) A.f1() B.f2(). `final` methods cannot be overridden, so `obj.f1()` always calls `A.f1()` regardless of the actual object type. `f2()` is an instance method that is overridden in `B`, so `obj.f2()` invokes `B.f2()` due to dynamic method dispatch.

Q: What is the output of this Java program?

A) Instance: 1, Static: 200. Static fields are part of the class, not the object's state, and are not serialized. The deserialized object will reflect the `staticCount` value present in the JVM at the time of deserialization.

Q: What does this Java code print?

A) y. Arrays in Java are 0-indexed. `letters[1]` accesses the element at index 1, which is the character 'y'.

Q1141 hard

In a complex `if` condition like `if (a > 10 && b < 5 || c == 0)`, which logical operator has the lowest precedence and therefore is evaluated last?

Q1142 hard code error

What kind of error will occur when executing the following Java code?

java

import java.util.concurrent.ArrayBlockingQueue;
import java.util.Queue;

public class QError3 {
    public static void main(String[] args) {
        Queue<Integer> abq = new ArrayBlockingQueue<>(1);
        abq.add(10);
        abq.add(20);
        System.out.println(abq.element());
    }
}

Q1143 hard

Given `byte b1 = 100; byte b2 = 50;`, which of the following expressions will compile without error and produce an `int` result equal to `150`?

Q1144 medium

In a class hierarchy, what is the correct order of constructor execution when an object of a subclass is created?

Q1145 medium code error

What is the compilation error in the following code?

java

class Parent {
    private void confidentialMethod() {
        System.out.println("Parent's confidential method");
    }
}

class Child extends Parent {
    @Override
    public void confidentialMethod() {
        System.out.println("Child's confidential method");
    }
}

Q1146 hard code output

What is the output of this code?

java

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

class ZeroHashItem {
    int value;
    public ZeroHashItem(int value) { this.value = value; }
    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ZeroHashItem that = (ZeroHashItem) o;
        return value == that.value;
    }
    @Override public int hashCode() { return 0; } // Constant hashCode
}

public class Main {
    public static void main(String[] args) {
        HashSet<ZeroHashItem> set = new HashSet<>();
        set.add(new ZeroHashItem(10));
        set.add(new ZeroHashItem(20));
        set.add(new ZeroHashItem(10));
        System.out.println(set.size());
    }
}

Q1147 medium

If an exception occurs in the `try` block and there is no matching `catch` block to handle it, what happens regarding the `finally` block?

Q1148 hard code output

What does this code print?

java

class A {
    public final void f1() { System.out.println("A.f1()"); }
    public void f2() { System.out.println("A.f2()"); }
}
class B extends A {
    @Override
    public void f2() { System.out.println("B.f2()"); }
}
public class Test {
    public static void main(String[] args) {
        A obj = new B();
        obj.f1();
        obj.f2();
    }
}

Q1149 easy code output

What is the output of this Java program?

java

import java.io.*;

class Counter implements Serializable {
    private int instanceCount;
    public static int staticCount = 0;

    public Counter(int i) {
        this.instanceCount = i;
        staticCount++;
    }

    public String toString() {
        return "Instance: " + instanceCount + ", Static: " + staticCount;
    }
}

public class Main {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Counter obj1 = new Counter(1);
        Counter.staticCount = 100; // Change static field before serialization

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(obj1);
        oos.close();

        Counter.staticCount = 200; // Change static field before deserialization

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        Counter deserializedObj = (Counter) ois.readObject();
        ois.close();

        System.out.println(deserializedObj);
    }
}

Q1150 easy code output

What does this Java code print?

java

public class ArrayTest {
    public static void main(String[] args) {
        char[] letters = {'x', 'y', 'z'};
        System.out.println(letters[1]);
    }
}

Q1151 hard code output

What is the output of this Java code?

java

import java.util.TreeMap;
import java.util.Iterator;
import java.util.Set;

public class Test {
    public static void main(String[] args) {
        TreeMap<Integer, String> map = new TreeMap<>();
        map.put(1, "One");
        map.put(2, "Two");
        map.put(3, "Three");

        Set<Integer> keys = map.keySet();
        Iterator<Integer> it = keys.iterator();
        while (it.hasNext()) {
            Integer key = it.next();
            if (key == 2) {
                map.put(4, "Four"); // Modifying map directly
            }
        }
        System.out.println(map.size());
    }
}

Q1152 medium

What happens if an exception is thrown from within a `finally` block, and there was already an exception pending from the `try` block?

Q1153 easy code error

What is the primary issue with this Java code snippet?

java

public class LoopError5 {
    public static void main(String[] args) {
        int x = 0;
        while (x < 2); // Semicolon here
            System.out.println("X: " + x);
        x++; // This statement is after the infinite empty loop
    }
}

Q1154 easy

What happens if a non-serializable object is referenced by a field in a serializable class, and that field is not marked `transient`?

Q1155 easy code output

What is the output of this code?

java

import java.util.HashSet;

public class Test {
    public static void main(String[] args) {
        HashSet<String> data = new HashSet<>();
        data.add("Hello");
        data.add(null);
        data.add("World");
        data.add(null); // Duplicate null
        System.out.println(data.size());
    }
}

Q1156 medium

Consider a Java class with an instance variable `int count` and a method that also declares a local variable `int count`. If `count` is referenced within that method without `this.`, which variable is accessed?

Q1157 easy code error

What compilation error will occur when compiling this Java code?

java

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

public class MyClass {
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new FileReader("nonexistent.txt"));
    }
}

Q1158 hard code error

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

java

public class Main {
    public static void main(String[] args) {
        var greeting = () -> System.out.println("Hello from lambda");
        greeting.run();
    }
}

Q1159 easy code output

What is the output of this code?

java

public class DataTypeTest {
    public static void main(String[] args) {
        char grade = 'A';
        System.out.println(grade);
    }
}

Q1160 hard

Which statement regarding method overriding and exception declarations in Java is true?

☕ Java MCQ Questions – Page 58