Java MCQ for Placement Top 100: Strong Your Coding Interviews:

Q.1 What is the result of the following code snippet?
int x = 10;
int y = 20;
int z = (x > y) ? x++ : y–;
System.out.println(z);
a) 10
b) 20
c) 21
d) 19

Answer: a) 10
Explanation: The conditional operator evaluates to the value of the expression on the true side if the condition is true, otherwise to the value of the expression on the false side. Here, since x > y is false, y– is evaluated and the value of y (20) is assigned to z.

Q.2 Which of the following statements about Java interfaces is false?
a) Interfaces can have constructors.
b) Interfaces can extend other interfaces.
c) Interfaces can have static methods.
d) Interfaces can have default methods.

Answer: a) Interfaces can have constructors.
Explanation: Interfaces cannot have constructors because they cannot be instantiated directly. They are implemented by classes, which provide their own constructors.

Q.3 What will be the output of the following code snippet?
int[] array = {1, 2, 3};
int sum = 0;
for (int i = 0; i <= array.length; i++) {
sum += array[i];
}
System.out.println(sum);
a) 6
b) 7
c) Compilation error
d) ArrayIndexOutOfBoundsException

Answer: d) ArrayIndexOutOfBoundsException
Explanation: The loop condition should be i < array.length instead of i <= array.length to prevent accessing an index beyond the bounds of the array.

Q.4 Which of the following statements about Java generics is true?
a) Generics allow runtime type checking.
b) Generics can be used with primitive data types.
c) Generics support covariant arrays.
d) Generics cannot be used with collections.

Answer: b) Generics can be used with primitive data types.
Explanation: Generics in Java can be used with reference types, including wrapper classes for primitive types, but not with primitive types themselves.

Q.5 What is the purpose of the ‘volatile’ keyword in Java?
a) It prevents a variable from being modified by multiple threads.
b) It ensures that a variable is visible to all threads.
c) It ensures that a variable’s value is never cached thread-locally.
d) It guarantees that a variable is initialized before it is accessed.

Answer: c) It ensures that a variable’s value is never cached thread-locally.
Explanation: The ‘volatile’ keyword in Java ensures that the value of a variable is always read from and written to main memory, rather than being cached thread-locally.

Q.6 What is the output of the following code snippet?
String str1 = “hello”;
String str2 = “hello”;
System.out.println(str1 == str2);
a) true
b) false
c) Compilation error
d) Runtime error

Answer: a) true
Explanation: String literals with the same value are interned, meaning they refer to the same object in memory. Therefore, str1 and str2 point to the same object.

Q.7 What does the ‘transient’ keyword do in Java?
a) It specifies that a variable cannot be modified.
b) It specifies that a variable is not to be serialized.
c) It specifies that a variable can only be accessed by methods within its own class.
d) It specifies that a variable can have a value of null.

Answer: b) It specifies that a variable is not to be serialized.
Explanation: The ‘transient’ keyword in Java is used to indicate that a variable should not be included in the serialization process.

Q.8 What is the purpose of the ‘strictfp’ keyword in Java?
a) It ensures that a class cannot be subclassed.
b) It restricts access to a method or variable.
c) It forces floating-point calculations to adhere to the IEEE 754 standard.
d) It enables assertions for a class.

Answer: c) It forces floating-point calculations to adhere to the IEEE 754 standard.
Explanation: The ‘strictfp’ keyword in Java ensures that floating-point calculations are performed in accordance with the IEEE 754 standard, providing platform-independent results.

Q.9 Which of the following is not a valid declaration of a Java method?
a) void method();
b) int method(int x);
c) static void method();
d) final int method();

Answer: d) final int method();
Explanation: Methods cannot be declared as both ‘final’ and ‘void’ or ‘final’ and have a return type.

Q.10 What is the output of the following code snippet?
int x = 5;
System.out.println(x++ * ++x);
a) 25
b) 30
c) 35
d) 40

Answer: c) 35
Explanation: The expression evaluates to 5 * 7 because x++ is post-incremented, so it uses the current value of x (5), and ++x is pre-incremented, so it uses the incremented value of x (6).

Q.1 Which of the following statements about Java constructors is true?
a) Constructors can be inherited.
b) Constructors can have a return type.
c) Constructors can be declared as final.
d) Constructors can be overloaded.

Answer: d) Constructors can be overloaded.
Explanation: Constructors in Java can be overloaded, meaning a class can have multiple constructors with different parameter lists.

Q.2 What is the output of the following code snippet?
int x = 10;
System.out.println(x++ + ++x);
a) 21
b) 22
c) 23
d) 24

Answer: c) 23
Explanation: The expression evaluates to 10 + 12 because x++ is post-incremented, so it uses the current value of x (10

Answer: c) internal
Explanation: ‘internal’ is not a valid access modifier in Java. The correct modifiers are private, protected, and public.

Q.4 What is the output of the following code snippet?
int[] numbers = {1, 2, 3, 4, 5};
int sum = 0;
for (int i = 0; i < numbers.length; i++) {
if (i % 2 == 0) {
continue;
}
sum += numbers[i];
}
System.out.println(sum);
a) 3
b) 6
c) 9
d) 12

Answer: b) 6
Explanation: The loop iterates over odd indices (i % 2 == 0) and adds their values to the sum.

Q.5 What is the purpose of the ‘finally’ block in Java exception handling?
a) It ensures that certain code is always executed, regardless of whether an exception is thrown or caught.
b) It specifies code that is executed when an exception occurs.
c) It indicates a block of code that should be skipped if an exception occurs.
d) It catches exceptions thrown by try blocks.

Answer: a) It ensures that certain code is always executed, regardless of whether an exception is thrown or caught.
Explanation: The ‘finally’ block in Java is used to ensure that certain code is always executed, regardless of whether an exception is thrown or caught.

Q.6 What is the correct syntax for a conditional (ternary) operator in Java?
a) if (condition) ? value1 : value2;
b) condition ? value1 : value2;
c) if (condition) then value1 else value2;
d) condition then value1 else value2;

Answer: b) condition ? value1 : value2;
Explanation: The ternary operator in Java has the syntax: condition ? value1 : value2.

Q.7 Which of the following statements about Java collections is true?
a) Arrays are part of the Java Collections Framework.
b) HashSet allows duplicate elements.
c) LinkedList is a synchronized collection.
d) TreeMap is not a sorted collection.

Answer: a) Arrays are part of the Java Collections Framework.
Explanation: Arrays are part of the Java Collections Framework, but they are not part of the java.util package.

Q.8 What is the purpose of the ‘static’ keyword in Java?
a) It makes a variable constant.
b) It enables methods and variables to belong to the class rather than an instance.
c) It ensures that a method cannot be overridden.
d) It allows access to the superclass methods and variables.

Answer: b) It enables methods and variables to belong to the class rather than an instance.
Explanation: The ‘static’ keyword in Java is used to declare methods and variables that belong to the class itself, rather than to instances of the class.

Q.9 Which of the following is not a valid Java identifier?
a) _variableName
b) 2variable
c) $variable
d) variableName

Answer: b) 2variable
Explanation: Java identifiers cannot start with a digit.

Q.10 What is the output of the following code snippet?
String str = “Hello”;
str.concat(” World”);
System.out.println(str);
a) Hello
b) World
c) Hello World
d) Null

Answer: a) Hello
Explanation: Strings in Java are immutable, so the concat() method returns a new string without modifying the original one.

What is an exception in Java?
a) A syntax error detected by the compiler
b) An event occurring during the execution of a program that disrupts the normal flow of instructions
c) A warning issued by the Java Virtual Machine (JVM)
d) An error caused by hardware malfunction

Answer: b) An event occurring during the execution of a program that disrupts the normal flow of instructions
Explanation: An exception in Java is an event that occurs during the execution of a program and disrupts the normal flow of instructions.

Which keyword is used to handle exceptions in Java?
a) try
b) catch
c) throw
d) all of the above

Answer: d) all of the above
Explanation: In Java, exceptions are handled using the try-catch blocks, and exceptions can also be thrown using the ‘throw’ keyword.

What is the purpose of the ‘finally’ block in exception handling?
a) To catch exceptions
b) To define code that will always be executed, regardless of whether an exception occurs or not
c) To throw exceptions
d) To handle checked exceptions

Answer: b) To define code that will always be executed, regardless of whether an exception occurs or not
Explanation: The ‘finally’ block in Java is used to define code that will always be executed, regardless of whether an exception occurs or not.

Which of the following exceptions is a checked exception in Java?
a) ArithmeticException
b) NullPointerException
c) IOException
d) ArrayIndexOutOfBoundsException

Answer: c) IOException
Explanation: IOException is a checked exception in Java, which means that it must be either caught or declared to be thrown by the method in which it may occur.

What is the output of the following code snippet?
try {
int num = Integer.parseInt(“ABC”);
System.out.println(num);
} catch (NumberFormatException e) {
System.out.println(“NumberFormatException occurred”);
}
a) ABC
b) NumberFormatException occurred
c) 0
d) Compilation error

Answer: b) NumberFormatException occurred
Explanation: The parseInt() method throws a NumberFormatException if the string cannot be parsed as an integer, so the catch block will be executed, printing “NumberFormatException occurred”.

Which of the following is NOT a standard exception class in Java?
a) RuntimeException
b) Exception
c) Throwable
d) Error

Answer: a) RuntimeException
Explanation: RuntimeException is a subclass of Exception and is used to represent exceptions that occur during the normal operation of the Java Virtual Machine (JVM).

What happens if an exception is thrown from within a ‘finally’ block?
a) The exception is caught by the nearest enclosing try-catch block.
b) The program terminates.
c) The exception is ignored.
d) The finally block is not executed.

Answer: a) The exception is caught by the nearest enclosing try-catch block.
Explanation: If an exception is thrown from within a ‘finally’ block, it is caught by the nearest enclosing try-catch block that can handle it.

Which keyword is used to explicitly throw an exception in Java?
a) try
b) catch
c) throw
d) throws

Answer: c) throw
Explanation: The ‘throw’ keyword is used to explicitly throw an exception in Java.

What is the difference between checked and unchecked exceptions in Java?
a) Checked exceptions are checked at compile time, while unchecked exceptions are checked at runtime.
b) Checked exceptions are checked at runtime, while unchecked exceptions are checked at compile time.
c) Checked exceptions are subclasses of RuntimeException, while unchecked exceptions are not.
d) Checked exceptions can be caught using a try-catch block, while unchecked exceptions cannot.

Answer: a) Checked exceptions are checked at compile time, while unchecked exceptions are checked at runtime.
Explanation: Checked exceptions are checked at compile time, meaning that the compiler ensures that they are either caught or declared to be thrown. Unchecked exceptions, on the other hand, are not checked at compile time and are typically subclasses of RuntimeException.

What is the superclass of all exception classes in Java?
a) Error
b) Throwable
c) Exception
d) RuntimeException

Answer: b) Throwable
Explanation: Throwable is the superclass of all exception classes in Java. Both exceptions and errors are subclasses of Throwable.