Java Collections Quiz

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Questions and Answers

What keyword is used to declare a new array in programming?

array

create

define

new (correct)

What will the first index of an array always be?

0 (correct)

-1

What is the default value of elements in a new String array when using the new method?

null (correct)

zero

empty string

undefined

What is an example of a perfect size array?

An array that holds fixed values like the days of the week Signup and view all the answers

What occurs when you attempt to store an int in a String array?

It generates a runtime error. Signup and view all the answers

What does it mean when an array is said to be a 'perfect size' array?

The array has a size fixed by the program context and element count matches allocated memory. Signup and view all the answers

How are perfect size arrays passed to methods in programming?

Using only the array’s reference Signup and view all the answers

Which of the following describes the use of initializer lists in array creation?

They set both the array's length and initialize its elements to specified values. Signup and view all the answers

What does the term 'indices' refer to in the context of an array?

The positions of elements within the array Signup and view all the answers

What default value does an integer array initialize its elements to when using the 'new' method?

0.0 Signup and view all the answers

What will be the output when printing an array without specifying an index?

The memory location of the array Signup and view all the answers

Which of the following is a common error when working with arrays?

ArrayIndexOutOfBoundsException Signup and view all the answers

How would you modify an element in an array?

Find the element's index and assign a new value to it Signup and view all the answers

What happens to a String array when initialized using the 'new' method?

It consists of null elements Signup and view all the answers

What is the final output when the cars ArrayList is processed?

A Prius is available. Signup and view all the answers

What will happen if grades.set(0, 42) is added after grades.add(98);?

The first grade will be replaced with 42. Signup and view all the answers

If you attempt to access an index that is out of range for an array, what is typically the result?

A runtime error will be thrown Signup and view all the answers

What does the following code snippet print: System.out.println(double[] decimals = new double)?

A reference to decimals in memory Signup and view all the answers

Which of the following would correctly modify the code to find the maximum grade?

int max = grades.get(0); for (int i : grades) { if (i > max) { max = i; } } Signup and view all the answers

What is the purpose of the line letters.remove(0) in the reversing code?

To remove the first letter in each iteration. Signup and view all the answers

Why is an enhanced for loop suitable for finding the minimum grade?

It does not change the elements of the ArrayList. Signup and view all the answers

What will the output be after reversing the letters ArrayList?

[E, D, C, B, A] Signup and view all the answers

What is the initial value of min before searching for the minimum grade?

The first element in the grades ArrayList. Signup and view all the answers

What is a key difference between the methods used to find the minimum and maximum grades?

Minimum uses less than, maximum uses greater than. Signup and view all the answers

What is the primary purpose of a 2D array?

To represent data in rows and columns like a table. Signup and view all the answers

When defining a 2D array, which syntax correctly initializes a 2D array with 3 rows and 2 columns?

String[][] names = new String[3][2]; Signup and view all the answers

Which statement correctly accesses the element in the second row and third column of a 2D array named 'data'?

data[1][2]; Signup and view all the answers

What is the correct way to print the number of columns in the first row of a 2D array named 'records'?

System.out.println(records[0].length); Signup and view all the answers

What does the following code snippet do: 'System.out.println(names.length + " rows");'?

Prints the number of rows in the 'names' 2D array. Signup and view all the answers

What technique is commonly used to populate a 2D array during its declaration?

Using an initializer list. Signup and view all the answers

How do you iterate through a 2D array using a regular for loop?

Using two nested for loops for rows and columns. Signup and view all the answers

Which of the following statements about 2D arrays is false?

The length property on a 2D array returns total elements in the array. Signup and view all the answers

What are 'formal parameters' in the context of a constructor?

Data types and names listed in the constructor header Signup and view all the answers

Which method call would move the turtle backward by 10 pixels?

t1.backward() Signup and view all the answers

What happens when a method call is executed in a program?

The statements within the method are executed before any following lines Signup and view all the answers

In the constructor example provided, what do (300,300) represent?

Actual parameters passed to the constructor Signup and view all the answers

What is indicated by the term 'call by value'?

Formal parameters receive copies of actual parameters Signup and view all the answers

Which of the following methods is used to change the color of the turtle?

t1.fillColor(Color.blue) Signup and view all the answers

What is the effect of a method's return value on control flow?

Control flow is returned to the point after the method was called Signup and view all the answers

Which statement correctly describes how programmers interact with methods?

Programmers can use methods based on understanding their purpose Signup and view all the answers

Study Notes

Working with ArrayLists

ArrayList Creation: Initialize an ArrayList with ArrayList cars = new ArrayList();
Element Addition: Use cars.add(element) to add elements like "Corolla", "Camry", "Prius", etc.
Element Availability Check: Use an enhanced for loop to determine if a specific element (e.g., "Prius") is available and update a string accordingly.
Printing Elements: Print the status of availability using System.out.println(Prius);.

Finding Minimum and Maximum Values

Finding Minimum: Set initial min to the first element of the grades ArrayList. Loop through elements and update min if a smaller value is found.
Finding Maximum: Similar to minimum, initialize max and check for larger values during iteration.
Enhanced for Loop: Utilizes a simpler syntax for iterating through collections.

Reversing ArrayList Elements

Element Access: Use regular for loops in reverse order to add elements back into the ArrayList.
Element Removal: Remove original elements from the ArrayList to keep only the reversed elements.
Index Management: Important to use remove(0) to continuously access the first element without skipping any.

Array Basics

Declaration: Declare an array with a name followed by new and defined data type (e.g., String[] names = new String[5];).
Default Values: New arrays automatically initialize to default values (null for strings, 0 for integers).
Array Indices: Start at 0; trying to access out-of-bounds results in ArrayIndexOutOfBoundsException.

Perfect Size Arrays

Definition: A perfect size array has a number of elements equal to the allocated memory.
Usage: Ideal for fixed data, such as days of the week where the size won’t change.
Array Method Parameters: Pass by reference, indicating the location in memory rather than the contents.

Modifying and Accessing Arrays

Element Modification: Access array elements using their index to assign new values.
2D Arrays: Defined with two sets of brackets (e.g., String[][] names = new String[rows][columns];).
Accessing in 2D Arrays: Use two indices to access and manipulate element positions within the array.

Array Method Calls

Method Functionality: Methods define behaviors for objects, including how to manipulate variables or perform actions.
Control Flow: Method calls interrupt sequence, executing all statements in the method before resuming.

Turtle Class Example

Method Examples: Methods like forward(), backward(), right(), and left() control the movement of a Turtle object.
Understanding Methods: Programmers can utilize methods without understanding their implementation, focusing on input-output behavior instead.

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Description

Test your knowledge of Java ArrayLists with questions on adding elements, searching for specific values, and finding minimum or maximum values. This quiz covers practical examples and common methods used with collections in Java.