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Quizzes > High School Quizzes > Technology

7.8.1 ArrayList Practice Quiz

Ace Your ArrayList Exam With Effective Practice Questions

Difficulty: Moderate
Grade: Grade 11
Study OutcomesCheat Sheet
Colorful paper art promoting a trivia quiz on Javas ArrayList operations for programming students.

What is the correct way to declare an ArrayList of Strings in Java?
ArrayList list = new ArrayList();
ArrayList list = new ArrayList();
ArrayList list = new ArrayList();
ArrayList list = new ArrayList();
This is the standard way to declare an ArrayList using generics. It ensures type safety by specifying that the list holds Strings.
Which import statement is required to use ArrayList in Java?
import java.util.List;
import java.util.ArrayList;
import java.io.ArrayList;
import java.ArrayList;
The ArrayList class is part of the java.util package, so you need to import it explicitly. This allows the Java compiler to locate the ArrayList class.
Which method is used to add an element to an ArrayList in Java?
add()
append()
insert()
put()
The add() method is specifically designed to insert elements into an ArrayList. Unlike other collection types, ArrayList does not use methods like append() or put().
How do you retrieve an element at a specific index in an ArrayList?
elementAt(index)
get(index)
retrieve(index)
access(index)
The get() method is used to fetch an element from an ArrayList at a specified index. This method provides direct access, similar to array indexing in a simple array.
Which method returns the number of elements in an ArrayList?
count()
length()
size()
total()
The size() method returns the number of elements currently stored in the ArrayList. The length() method is used with arrays, not with ArrayLists.
What is the difference between remove(int index) and remove(Object o) in an ArrayList?
The first method removes all matches of the object, while the second removes only one.
Both methods remove an element at a specific index.
The first removes an element at a specific index, while the second removes the first occurrence of the specified object.
There is no difference; they are overloaded with the same behavior.
remove(int index) operates by removing the element at the specified index, whereas remove(Object o) searches for the first occurrence of the provided object and removes it. Understanding this distinction is key when manipulating ArrayLists.
What will happen if you try to access an ArrayList with an index that is out of bounds?
It returns the first element.
It returns null.
It adds a new element automatically.
It throws an IndexOutOfBoundsException.
Accessing an element at an index that doesn't exist in the ArrayList will result in an IndexOutOfBoundsException. This is Java's built-in mechanism to signal invalid index accesses.
What method can be used to change the element at a specific index in an ArrayList?
change(index, element)
set(index, element)
replace(index, element)
update(index, element)
The set() method is used to replace the element at a specific index with a new element. This operation is fundamental when updating the contents of an ArrayList.
How does the ArrayList manage its internal storage when new elements are added beyond its current capacity?
It creates a new list each time an element is added.
It resizes its internal array automatically.
It uses a linked list for storage.
It never resizes; it has a fixed size.
ArrayList manages dynamic storage by automatically resizing its internal array when the existing capacity is exceeded. This dynamic resizing is a key feature that distinguishes it from fixed-size arrays.
Which method can be used to check if an ArrayList contains a specific element?
find(element)
exists(element)
contains(element)
has(element)
The contains() method is provided by ArrayList to check for the presence of an element. It returns true if the element is found, making it easy to verify membership within the list.
If an ArrayList is declared with a generic type, what happens if you try to add an element of a different type?
The incompatible element is simply ignored.
The element is automatically converted to the generic type.
A runtime error occurs.
A compile-time error occurs.
Generics enforce type constraints at compile time, preventing you from adding elements of an incompatible type. This feature helps catch errors early in the development cycle.
What does the trimToSize() method do in an ArrayList?
It clears the ArrayList of all elements.
It shortens the list by removing unused elements.
It trims the capacity of the ArrayList to its current size.
It reduces the size of each element in the list.
The trimToSize() method is used to adjust the capacity of the ArrayList so that it matches the current number of elements. This can help in saving memory if no additional elements are expected to be added.
What is the output of the following code? ArrayList numbers = new ArrayList<>(); numbers.add(10); numbers.add(20); System.out.println(numbers.get(1));
1
The code will not compile.
10
20
ArrayList is zero-indexed in Java, which means that numbers.get(1) returns the second element, 20. This demonstrates basic indexing in Java collections.
What happens when you remove an element from the middle of an ArrayList?
The entire ArrayList is reset.
Subsequent elements shift right, leaving a gap.
Subsequent elements shift left to fill the gap.
The removed element remains in the list as null.
When an element is removed from an ArrayList, all elements to its right shift left to maintain a contiguous sequence. This behavior ensures that the list does not have gaps between elements.
Which statement about ArrayList's performance is true?
Removing an element is always done in constant time (O(1)).
Searching for an element is faster than accessing by index.
Inserting an element in the middle always has constant time complexity (O(1)).
Accessing elements by index has constant time complexity (O(1)).
Random access in an ArrayList is an O(1) operation because it uses an underlying array. However, insertion and deletion may require shifting elements, leading to higher time complexities.
Consider an ArrayList of Integers declared as ArrayList list = new ArrayList<>(Arrays.asList(1,2,3,4,5)); What is the effect of calling list.subList(1,4).clear() on the list?
It throws an UnsupportedOperationException.
The elements 1, 2, and 3 are removed, resulting in [4, 5].
The call has no effect because subList returns a copy of the list.
The elements 2, 3, and 4 are removed, resulting in [1, 5].
The subList method creates a view of the original list between the specified indices. Calling clear() on this view removes the elements at index 1, 2, and 3, leaving the list as [1, 5].
How can you convert an ArrayList to an array of Strings in Java?
Using list.toArray(new String[0])
Using list.array()
Using list.toArray(String[].class)
Casting the list directly to (String[])
The toArray(T[] a) method is the standard way to convert an ArrayList to an array in Java. The idiom new String[0] is commonly used because it allows the method to return an array of the correct type.
In a multi-threaded environment, why might ArrayList be problematic and what alternative should be used?
ArrayList locks the entire collection on every operation, which is inefficient.
ArrayList allows concurrent modifications, making it thread-safe.
ArrayList is not thread-safe and Vector or CopyOnWriteArrayList should be used.
ArrayList automatically synchronizes on each method call.
ArrayList does not provide inherent synchronization, meaning it is not safe for concurrent modifications by multiple threads. Alternatives like Vector or CopyOnWriteArrayList are designed to handle concurrent access.
What is the time complexity of the add() operation in an ArrayList when the underlying array needs to be resized?
Always O(1) regardless of resizing.
O(n log n) due to element shifts.
Amortized O(1), but worst-case O(n).
Always O(n^2) due to resizing operations.
Typically, the add() operation works in constant time on average (amortized O(1)). However, when the internal array is full and needs resizing, the operation may require copying all elements, resulting in a worst-case time of O(n).
How would you safely remove elements from an ArrayList while iterating over it without causing a ConcurrentModificationException?
Create a copy of the ArrayList and iterate over the copy while modifying the original.
Use an Iterator and call its remove() method.
Use a traditional for loop and remove by index without precautions.
Use a for-each loop and call list.remove().
The safest way to remove elements during iteration is by using an Iterator and its remove() method. This avoids the ConcurrentModificationException that occurs with direct modifications during iteration.
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Study Outcomes

  1. Understand how to declare, instantiate, and initialize an ArrayList in Java.
  2. Analyze ArrayList methods such as add, remove, get, and set for effective element manipulation.
  3. Apply ArrayList operations to solve programming problems and modify data structures dynamically.
  4. Evaluate the advantages and limitations of using ArrayList compared to traditional arrays.
  5. Debug and optimize Java code that leverages ArrayList functionalities for improved performance.

7.8.1 ArrayList Quiz: Practice & Review Cheat Sheet

  1. Create an ArrayList - Skip fixed-size hassles by using ArrayList. Just write ArrayList<Type> listName = new ArrayList<Type>(); and enjoy a list that expands on demand. ArrayList (Java SE 24 & JDK 24)
    2. ArrayList (Java SE 24 & JDK 24)
  2. Add elements with add() - Stick new items at the end of your list with add(). Just call listName.add(element); and boom - your element joins the party instantly. It's that simple! ArrayList add(E) Method
    3. ArrayList add(E) Method
  3. Access elements with get() - Grab items from your ArrayList by using get(index). This returns the element at the chosen position, so you can read or manipulate it. Watch out for IndexOutOfBoundsException if you go too far! ArrayList get(int) Method
    4. ArrayList get(int) Method
  4. Remove elements with remove() - Toss out unwanted items with remove(index). This pulls the element at the given spot and shifts the rest back smoothly. Perfect for cleaning up your list on the fly. ArrayList remove(int) Method
    5. ArrayList remove(int) Method
  5. Replace elements with set() - Swap in fresh data using set(index, element). This replaces the existing item at your chosen position without changing list size. It's the fastest way to update data in place. ArrayList set(int, E) Method
    6. ArrayList set(int, E) Method
  6. Check for elements with contains() - Verify if the list has a specific item by calling contains(element). This returns true or false, ensuring you know if your search succeeded. Great for conditional logic before more operations. ArrayList contains(Object) Method
    7. ArrayList contains(Object) Method
  7. Find element index with indexOf() - Locate where an item lives using indexOf(element). You'll get the first occurrence's index or -1 if it's missing. Super handy for pinpointing data within your dynamic array. ArrayList indexOf(Object) Method
    8. ArrayList indexOf(Object) Method
  8. Get the size with size() - See how many items you've got with size(). This nifty method returns the current list count, so you can track your collection length. No more guessing or manual counts! ArrayList size() Method
    9. ArrayList size() Method
  9. Iterate with forEach or for-each loop - Loop through your list effortlessly using a for-each loop: for (Type item : listName) { /* process item */ }. You can also embrace functional flair with listName.forEach(...). Perfect for clean, concise iteration! ArrayList forEach(Consumer) Method
    10. ArrayList forEach(Consumer) Method
  10. Compare ArrayList and array - Remember: arrays are fixed-size, but ArrayLists flex as you add or remove elements. Use arrays for raw speed and low overhead, and ArrayLists for convenience and dynamic sizing. Picking the right tool makes your code both efficient and maintainable. The List Interface (Java Tutorials)
    11. The List Interface (Java Tutorials)
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