Test Study Weeks 4-7

Question 1

What are the two types of methods in Java?

Answer 1

Void methods perform a task and terminate, while value-returning methods return a value to the caller.

Question 2

What are the key components of a method declaration?

Answer 2

Modifiers, return type, method name, and parameter list.

Question 3

What is a method signature?

Answer 3

A method’s name and parameter list (number, type, and order of parameters).

Question 4

How do you call a method in Java?

Answer 4

By using its name followed by parentheses: methodName();

Question 5

What is the difference between arguments and parameters?

Answer 5

Arguments are values passed to a method; parameters are the variables that receive those values.

Question 6

How does Java pass primitive data types to a method?

Answer 6

By value, meaning a copy of the value is passed, and modifications inside the method do not affect the original variable.

Question 7

What happens when an object reference is passed to a method?

Answer 7

The memory address of the object is passed, so changes made inside the method affect the original object.

Question 8

Why are Strings immutable in Java?

Answer 8

Once created, String objects cannot be modified. Changing a String creates a new object.

Question 9

What is a local variable?

Answer 9

A variable declared inside a method that is accessible only within that method.

Question 10

How do you return a value from a method?

Answer 10

Using the return statement followed by a value. Example: return number * 2;

Question 11

What is an array in Java?

Answer 11

A collection of elements of the same data type, stored in contiguous memory locations.

Question 12

How do you declare and initialize an array?

Answer 12

int[] numbers = new int[5]; or int[] numbers = {1, 2, 3, 4, 5};

Question 13

What is zero-based indexing?

Answer 13

Arrays start indexing at 0, so the first element is at index 0.

Question 14

Can you change the size of an array after creation?

Answer 14

No, arrays have a fixed size once initialized.

Question 15

How do you access an array element?

Answer 15

Using its index: numbers[0] = 10; assigns 10 to the first element.

Question 16

What happens if you access an array out of bounds?

Answer 16

Java throws an ArrayIndexOutOfBoundsException.

Question 17

How do you find the length of an array?

Answer 17

Using the length property: array.length;

Question 18

What is an off-by-one error?

Answer 18

A common mistake where a loop iterates one index too far, causing an exception.

Question 19

How do you iterate over an array?

Answer 19

Using a for loop: for (int i = 0; i < array.length; i++) or an enhanced for loop: for (int num : array).

Question 20

How do you copy an array correctly?

Answer 20

Using a loop: for (int i = 0; i < arr1.length; i++) arr2[i] = arr1[i];

Question 21

What happens when you assign one array reference to another?

Answer 21

Both references point to the same array, not a copy.

Question 22

How do you compare two arrays for equality?

Answer 22

Using Arrays.equals(arr1, arr2) for content comparison (not ==, which checks references).

Question 23

What is a partially filled array?

Answer 23

An array where some elements are unused, tracked with a separate counter variable.

Question 24

What is a two-dimensional array?

Answer 24

An array of arrays, arranged in rows and columns. Example: int[][] matrix = new int[3][4];

Question 25

What is a ragged array?

Answer 25

A 2D array where rows have different lengths.

Question 26

How do you sum all elements in a 2D array?

Answer 26

Using nested loops: for (int row = 0; row < matrix.length; row++) for (int col = 0; col < matrix[row].length; col++) total += matrix[row][col];

Question 27

What is a class in Java?

Answer 27

A blueprint for creating objects, containing fields (data) and methods (behavior).

Question 28

What is an object?

Answer 28

An instance of a class with unique values for its fields.

Question 29

What are instance variables?

Answer 29

Variables that belong to each object of a class and store its state.

Question 30

What are instance methods?

Answer 30

Methods that operate on an object's instance variables.

Question 31

What is data hiding?

Answer 31

A principle where instance variables are kept private and accessed through methods.

Question 32

What are accessor and mutator methods?

Answer 32

Accessors (getters) return field values, and mutators (setters) modify them.

Question 33

What is a constructor?

Answer 33

A special method that initializes an object when it is created.

Question 34

What are the characteristics of a constructor?

Answer 34

1) Same name as the class. 2) No return type. 3) Called automatically when an object is created.

Question 35

What is a no-arg constructor?

Answer 35

A constructor with no parameters that sets default values.

Question 36

What is constructor overloading?

Answer 36

Defining multiple constructors with different parameter lists.

Question 37

What is method overloading?

Answer 37

Defining multiple methods with the same name but different parameters.

Question 38

What is the this keyword used for?

Answer 38

Refers to the current object, useful for distinguishing between instance variables and parameters.

Question 39

What is the toString method?

Answer 39

A method that returns a string representation of an object.

Question 40

What happens when toString is not overridden?

Answer 40

It prints the memory address of the object.

Question 41

What is the equals method used for?

Answer 41

Compares object contents instead of memory addresses.

Question 42

What is a copy constructor?

Answer 42

A constructor that creates a new object as a copy of an existing one.

Question 43

What is object aggregation?

Answer 43

When an object contains a reference to another object ("has-a" relationship).

Question 44

What is method chaining?

Answer 44

Calling multiple methods on the same object in one statement: obj.method1().method2();

Question 45

What is the static keyword used for?

Answer 45

Declares class-level variables and methods shared among all instances.

Question 46

How do you call a static method?

Answer 46

Using the class name: Math.sqrt(25);

Question 47

What is garbage collection?

Answer 47

Automatic memory management that removes unreferenced objects.

Question 48

What is a null reference?

Answer 48

A reference that does not point to any object.

Question 49

How do you check if a reference is null?

Answer 49

if (obj != null) { ... }

Question 50

What is shadowing in Java?

Answer 50

When a local variable has the same name as an instance variable, hiding it.

Question 51

What is a package in Java?

Answer 51

A way to organize related classes in separate namespaces.

Question 52

How do you import a package?

Answer 52

import java.util.Scanner; or import java.util.*;

Question 53

What is the difference between == and .equals() in Java?

Answer 53

== compares memory addresses, while .equals() compares actual content.

Question 54

What is a deep copy vs. a shallow copy?

Answer 54

A deep copy creates a new object with copied values; a shallow copy copies the reference.

Question 55

What is the purpose of the super keyword?

Answer 55

Calls a parent class's constructor or method.

Question 56

What is polymorphism?

Answer 56

The ability of different classes to use the same method names, often through method overriding.

Question 57

What is an interface in Java?

Answer 57

A collection of abstract methods that a class can implement.