Week 7-12

Question 1

What are the three different types of errors in java.

Answer 1

Internal errors - Unrecoverable. E.g. OutOfMemoryError
Unchecked exceptions - RuntimeException error in code. E.g. IllegalArgumentException
Checked exceptions - Something wrong outside of your control. E.g. FileNotFoundException.

Question 2

Distinguish between making a checked and unchecked exception.

Answer 2

checked: extend Exception class
unchecked: extend RuntimeException class

Question 3

Distinguish between function, statement, branch and condition coverage.

Answer 3

F: Every function has been tested at least once.
S: Every statement within code has been tested, all lines of code reached.
B: Every possibility for each statement is executed (true and false)
C: Every possibility for each part of the condition.

Question 4

Syntax for an anonymous inner class called area of type calculator.

Answer 4

Calculator area = new Calculator() {

@Override
public double calculate(double width, double height) {
return width * height;
}

};

Question 5

What is SAM?

Answer 5

Single abstract method. Essentially an anonymous function which implements a functional interface.

Question 6

What is a functional interface?

Answer 6

An interface with only one method.
Declared with @FunctionalInterface

Question 7

Syntax for a SAM called area of type calculator. Give both method without parameter typing and with.

Answer 7

Calculator area = (width, height) -> width * height;

Calculator area = (double width, double height) -> {
return width * height;
};

Question 8

What is advantage of switch with lambda?

Answer 8

Allows sets of values in case statement joined by coma.

E.g. case 1,2 -> sout(“Number less than three”);

Question 9

What is Person::compareTo?

Answer 9

A method reference.

Question 10

Syntax for stream API?

Answer 10

List<Type> listName = originalList.stream()
.instruction
.instruction ...
.collect(Collectors.toList());</Type>

Question 11

What are the two main challenges of threading and concurrency?

Answer 11

Deadlock: when threads are waiting for each other, but neither is running.
Livelock: when threads are running but not responding / updating some state.

Question 12

Explain thread methods. run, start, sleep, wait and join.

Answer 12

run: he process body of the Thread; defines what it will do
start: schedules the Thread and at some point calls run
sleep: suspends the Thread for n milliseconds
wait: suspends the Thread for a period of time, until some
other state is reached
join: suspend the Thread until some other Thread has terminated

Question 13

Why are lambda expressions used for threading?

Answer 13

Because runnable is a SAM interface.

Question 14

How you can stop threads counting the same thing twice? Two methods.

Answer 14

Make the mutator method synchronized with keyword after visibility before return type.

synchronized (counter) {
counter.increment();
counter.notifyAll();
}

Question 15

Which of the following best describes a principle of good object
design?

1. Using only primitive data types in a class to reduce memory
   overhead.
2. Ensuring all class methods are public to maximize reusability.
3. Designing classes so they depend on specific concrete
   implementations rather than abstractions.
4. Avoiding the use of constructors to allow greater flexibility in
   object creation.
5. Encapsulating behavior and data within a class to minimize
   interaction with unrelated classes.

Answer 15

5

Question 16

What is a key benefit of polymorphism in object-oriented
programming?
1. A. It allows a single method to accept many different types of
argument.
2. It eliminates the need for defining interfaces in code.
3. It enables a method or object to behave differently depending
on the runtime type of the object
4. It enforces strict compile-time type checking for all method
calls.
5. It enables the ability to override many methods in the super
class to provide flexibility.

Answer 16

3

Question 17

Which of the following statements about encapsulation in Java is correct?

1. Encapsulation is implemented by using final keyword with variables.
2. Encapsulation ensures that all methods in a class are public.
3. Encapsulation allows restricting access to internal data using access modifiers like private.
4. Encapsulation is only applicable to primitive data types.
5. Encapsulation requires using abstract classes and interfaces.

Answer 17

3

Question 18

Which of the following is a valid use of a functional interface in Java?

1. Defining a class that implements multiple methods from an interface.
2. Creating an anonymous class that overrides a single abstract method.
3. Using a functional interface to define constants for a class.
4. A functional interface can have more than one abstract method but must include static methods.
5. Lambda expressions can only be used with interfaces that extend Runnable

Answer 18

2

Question 19

What will happen if a subclass overrides a method declared final in the superclass?

1. The method in the subclass will be treated as a completely separate method.
2. The code will compile successfully, but the overridden method will not be executed.
3. The program will throw a runtime exception when the subclass method is called.
4. The code will fail to compile with a “cannot override final method” error.
5. The overridden method will still call the original superclass implementation.

Answer 19

4

Question 20

Principle of error handling in java.

Answer 20

Throw early, catch late.

Question 21

What happens when an exception is thrown in a try block but there is no matching catch block?

1. The program will terminate immediately without executing the finally block.
2. The exception is ignored, and the program continues execution.
3. The exception will propagate to the method’s caller.
4. The exception will be automatically handled by the JVM and execution will resume.
5. The program will execute the finally block and terminate gracefully.

Answer 21

3

Question 22

T or F. The finally block will always execute even if there is no matching catch.

Answer 22

True.

Question 23

What is serialization in java?

Answer 23

The conversion of the state of an object into a byte stream.

Question 24

When is a nullPointerException thrown?

Answer 24

At runtime, when we attempt to dereference an object with value NULL.

Question 25

If you attempt to catch an Exception and then catch a more specific exception such as IllegalArgument what will happen?

Answer 25

Code will not compile

Question 26

What will happen if a Serializable class does not implement the Serializable interface and you attempt to serialize an instance of it? 1. The program will compile, but serialization will fail at runtime with a NotSerializableException. 2. The program will fail to compile due to missing Serializable implementation. 3. The program will compile and serialize the object without any issues. 4. The program will throw a runtime exception when the object is serialized. 5. The program will throw a ClassCastException at compile time.

Answer 26

1 Because Serializable has no methods.

Question 27

Which of the following is a valid way to define a lambda expression for the Runnable interface in Java? (Multiple correct) 1. Runnable r = () -> { System.out.println("Running!"); }; 2. Runnable r = { System.out.println("Running!"); }; 3. Runnable r = () -> System.out.println("Running!"); 4. Runnable r = (String msg) -> System.out.println(msg); 5. Runnable r = () -> { System.out.println("Running!"); return; };

Answer 27

1 and 3, runnable interface has no parameters

Question 28

What is loose coupling in java?

Answer 28

Classes depend on each other but are unaware of each other’s implementation details.

Question 29

What is the factory method pattern?

Answer 29

To create objects in a superclass but allow subclasses to alter the type of objects that will be created.

Question 30

What happens if a class implements two interfaces with conflicting default methods? 1. The class will be forced to override the conflicting methods. 2. The class will compile, but the default methods will be ignored. 3. The class will inherit both default methods, and no compilation error will occur. 4. The class will not compile unless one of the interfaces is removed. 5. The class will throw an exception at runtime.

Answer 30

1

Question 31

What is true about the variables used in a lambda expression? 1. Lambda expressions can only use local variables that are final or effectively final. 2. Lambda expressions can modify local variables. 3. Lambda expressions cannot access variables outside their scope. 4. Variables used in lambda expressions must be static. 5. Variables used in lambda expressions must be declared as final.

Answer 31

1

Question 32

Which of the following is true about inheritance in Java? 1. A subclass can inherit private members of its superclass. 2. A subclass can access only public members of its superclass. 3. A subclass can inherit both public and private members of its superclass. 4. A subclass can override the constructor of its superclass. 5. A subclass cannot inherit members from its superclass.

Answer 32

2

Question 33

Which of the following is an example of polymorphism using an interface in Java? 1. A class implements multiple interfaces and overrides the methods from all of them. 2. A subclass inherits all methods from its superclass. 3. A method in a subclass is called even though it is defined in an interface. 4. A method in a class overrides a method in the interface without using the implements keyword. 5. An interface can inherit another interface and provide default method implementations.

Answer 33

1

Question 34

What happens when a serialized class is changed (e.g., field added or removed) between serialization and deserialization? 1. The deserialization will fail if the serial version UID is changed. 2. Deserialization will succeed and ignore the new fields. 3. The new field will be automatically assigned a default value during deserialization. 4. The system will throw a ClassNotFoundException. 5. It causes a ClassCastException at runtime.

Answer 34

1

Question 35

What is the primary advantage of using buffered streams (like BufferedReader and BufferedWriter) over unbuffered streams? 1. They provide automatic handling of exception cases. 2. They offer faster reading and writing by reducing the number of read/write operations on the disk. 3. They can handle both binary and text data seamlessly. 4. They automatically close the file when reading or writing is complete. 5. They support serialization of objects.

Answer 35

2

Question 36

Which class is used for reading bytes directly from a file in Java? BufferedReader FileReader FileInputStream ObjectInputStream Scanner

Answer 36

FileInputStream

Question 37

Which of the following classes in Java is used to serialize objects? ObjectOutputStream ObjectInputStream FileOutputStream PrintStream DataOutputStream

Answer 37

Object output stream (serializes) Object input stream (deserializes)

Question 38

Which class in Java is used to get metadata information about a class at runtime using reflection? Class Object Reflection Method Constructor

Answer 38

Class

Question 39

Which of the following methods in the Class class can be used to create a new instance of a class dynamically using reflection? newInstance() getConstructor() newObject() getClass() invoke()

Answer 39

newInstance()

Question 40

String s1 = "abc"; String s2 = "abc"; System.out.println(s1 == s2); What is the output?

Answer 40

true

Question 41

Define abstraction.

Answer 41

Hiding implementation details using interfaces.

Question 42

Define overloading.

Answer 42

Creating multiple methods with the same name but different parameters.

Question 43

Define polymorphism.

Answer 43

Allowing objects to take many forms based on their behaviour.

Question 44

Define encapsulation.

Answer 44

Involves hiding implemention details by combining data and methods that operate on that data into a single unit called a class. While still allowing external access to the methods.

Question 45

Which keyword is used in Java to achieve runtime polymorphism?

Answer 45

override