StringBuilder and Stringbuffer Flashcards
In Java, the _________ is used to
represent a group of characters.
String class
It is one of the most frequently
used classes in Java programming.
String
When a new string is created,
memory is ________ for it.
allocated
String Literals
Created using __________
Stored in the ____
double quotes
String Pool
If the same value already exists in the pool, Java
_______ it instead of creating a new one.
reuses
_________: Memory is allocated and
freed as the program runs.
Dynamic
________________________
Created using the new keyword or
__________.
Stored in the Heap (general memory area for
objects).
Each new keyword creates a new instance, even
if the value is the same.
Dynamically Constructed Strings
concatenation
The _______ is like a large warehouse
where Java stores data(e.g., Strings,
Cars, Dogs).
Heap
The Heap is like a ________
where Java stores data(e.g., Strings,
Cars, Dogs).
large warehouse
_________: Java
automatically ____________ to
free up memory.
Garbage Collection
removes unused data
_________ (String Constant Pool)
A special area within the _______ for __________
String Pool
Heap
storing strings
_________by reusing identical
strings.
Saves memory
__________ by avoiding
duplicate data.
Improves performance
__________ by avoiding
duplicate data.
Improves performance
Saves memory by reusing ______________.
identical
strings
Improves performance by avoiding
__________.
duplicate data
String Pool (String Constant Pool)
How It Works:
When a string literal is created (e.g.,
“Hello “), Java checks ___________ in the pool.
If it exists, Java returns a _________ to
the existing string.
If it doesn’t exist, Java creates a ____________ and returns its
reference.
if it already exists
reference
new
string in the pool
____________: General memory for ____, _________, and managed by _______.
Heap
data
dynamic
garbage collection
___________: Special memory for strings, optimized for
reuse and efficiency.
String Pool
Use _______ (“text”) for memory efficiency and
new for unique instances.
string literals
Use string literals (“text”) for ___________ and
new for _____________.
memory efficiency
unique instances
String Pool: __________ for strings, optimized for
________ and ________.
Special memory
reuse
efficiency
Strings in Java are ____________, meaning their
values cannot be changed after creation.
immutable
Any operation that seems to modify a string (e.g.,
concatenation, replacement) actually creates a
_________.
new string
This behavior can lead to_______________,
especially when performing frequent ______________.
higher memory usage
string manipulations
However, _____________ efficiently
manages memory by cleaning up _____________.
Java’s garbage collector
unused string data
Immutability means
You cannot change the content of the
box directly
________ is like giving a copy of the
toy to your friend.
Immutability
In Java, immutability ensures predictable
and ________________, especially when multiple
parts of a program use the same text.
safe behavior
Why It’s Important:
Prevents _____________ (two threads
updating the same data simultaneously).
Avoids _________________ (threads seeing
incorrect or partial data).
Prevents ______________ or
_________.
race conditions
data inconsistency
unexpected crashes
unpredictable behavior
______________ensures that multiple threads can
access shared data without causing errors or
corruption.
Thread safety
_______________________
Perform one task at a time.
Slower for multiple tasks.
Single-Threaded Programs
_______________
Perform multiple tasks simultaneously.
Faster and more efficient.
Multi-Threaded Programs
Use multi-thread for complex programs (e.g.,
video streaming, chat apps, web servers).
complex programs
In Java, a __________________ is a special method used
for initialization. A _____________ sets up the
initial state by assigning values or
allocating memory.
constructor
In Java, a constructor is a special method used
for ______________. A constructor sets up the
___________ by ____________ or
_________
initialization
initial state
assigning values
allocating memory
In terms of ___________, a constructor is
used to initialize a __________ with a
default or specified value. The _______ class provides several constructors that allow different ways to create
a _________ instance.
StringBuilder
new StringBuilder
StringBuilder
StringBuilder
In terms of StringBuilder, a ____________ is
used to _____ a new StringBuilder with a
______ or __________. The StringBuilder class provides several constructors that allow different ways to create a StringBuilder instance.
constructor
initialize
default
specified value
Initializes an ___________ with a default
capacity of _________.
empty StringBuilder
16 characters
Creates a StringBuilder with a _________ (useful
when handling large strings to reduce memory reallocation).
custom capacity
Creates a StringBuilder initialized with the given _________.
string value
The initial capacity is ________ of the string.
16 + length
A _____________ is a general representation of character sequences (like String and StringBuffer).
CharSequence
A CharSequence is a ____________ of character sequences (like String and StringBuffer).
general representation
A CharSequence is a general representation of character sequences (like _________________).
String and StringBuffer
This constructor allows initializing a ______ using a __________ or another___________.
StringBuilder
StringBuffer
CharSequence
The ____________ in Java provides various methods to manipulate string sequences efficiently.
StringBuilder class
The StringBuilder class in Java provides various methods to ___________________________.
manipulate string sequences efficiently
Adds the specified text at the end of
the existing StringBuilder content.
append(String s)
The__________ method returns the same StringBuilder
instance, allowing method chaining.
append()
The append() method returns the same StringBuilder
instance, allowing__________.
method chaining
append() is _______ – modifies the existing
StringBuilder instead of creating a new data.
efficient
___________ – You can chain multiple append() calls.
Method chaining
_____________ – Works well with
Scanner for dynamically building text.
Ideal for user input processing
Inserts the specified text at the given
index (offset).
StringBuilder.insert(int offset, data);
____ → The index position where the data
should be inserted.
offset
_____ → The value to be inserted (can be a
String, char, int, double, etc.).
data
The _______ method modifies the existing
StringBuilder data without creating a new one.
insert()
insert() is _____ – allows adding new data at any
position without replacing existing content.
useful
___________– unlike replace(), it does not
overwrite characters.
Preserves existing text
__________– works well with
Scanner for building dynamic text.
Great for user input manipulation
Replaces the characters between start and end
indexes with the specified string.
replace(int start, int end, String str)
______→ The starting index (inclusive) where replacement begins.
start
______→ The ending index (exclusive) where replacement
stops.
end
____ → The new string that will replace the existing
characters in the given range.
str
The ________ method modifies the existing StringBuilder data without creating a new one
replace()
Initializes an ___________ with a default
capacity of 16 characters.
empty StringBuilder
Creates a StringBuilder with a ______________(useful
when handling large strings to reduce memory reallocation).
custom capacity
Creates a StringBuilder initialized with the__________.
given string value
The initial capacity is _______ of the string.
16 + length
The StringBuilder class in Java provides various ____________ to manipulate string sequences efficiently.
methods
replace() is ______ – modifies the existing
StringBuilder without creating a_______.
efficient
new data
It replaces only a portion of the text – unlike
__________, which changes a single character.
setCharAt()
Uses index positions – you must specify __ and ______for replacement.
start
end indexes
Deletes characters between the specified
start and end indexes.
delete(int start, int end)
Description: Deletes characters between the specified
start and end indexes.
______→ The starting index (inclusive) where deletion
begins.
______→ The ending index (exclusive) where deletion
stops.
______method modifies the existing StringBuilder
without creating a new one.
start
end
The delete()
delete(int start, int end)
Key Takeaways
✔ delete() _____________– modifies the
existing StringBuilder without creating a new Stringbuilder.
✔ It ________________ – unlike
setLength(0), which clears the entire content.
✔ Uses___________ – you must specify start and end
indexes for deletion.
✔ Works well for__________ – great for removing
______ from user input.
removes text efficiently
removes only a portion of the text
index positions
string manipulation
unnecessary words
______________
Description: Removes a single character at the
specified index.
________ → The position of the character to be
removed.
The ___________method modifies the existing
StringBuilder instead of creating a new one.
Usage: Useful for______________ without
affecting the rest of the string.
deleteCharAt(int index)
index
deleteCharAt()
deleting a single character
- deleteCharAt(int index)
Key Takeaways
✔ deleteCharAt() removes a____ efficiently
– modifies the StringBuilder directly.
✔_______ – unlike delete(), which removes a
range of characters.
✔ Useful for ______ – removing spaces,
typos, or unwanted characters.
✔ ________ is important – always check if the index
is valid before using deleteCharAt().
single character
Requires an index
correcting user input
Error handling
Useful for correcting user input – ___________,
_____, or ____________.
removing spaces
typos
unwanted characters
Error handling is important – always check if the index
is ______ before using deleteCharAt().
valid
_____
Description: Reverses the sequence of characters in
the StringBuilder.
This method modifies the existing StringBuilder in
place.
The __________ is transformed into its reversed
version
Usage: Helps in reversing strings for ___________- or
_____________.
reverse()
original string
palindromes
algorithmic processing
______ is useful for reversing words and sentences
– modifies the StringBuilder directly.
✔ _______ – does not create a new instance of the
variable, works in-place.
✔ Can be used for ____________ – reversing a
string and comparing it with the original.
✔ Works on any________ – words, sentences,
numbers, etc.
reverse()
Efficient
palindrome checking
text format
✔ Works on any text format – ______, _______,
________, etc.
words
sentences
numbers
________
Description: Returns the current capacity (________) of the StringBuilder.
___________ refers to the __________ the
StringBuilder can hold before it needs to
resize.
capacity()
storage size
Capacity
number of characters
_____________ = StringBuilder.capacity();
int currentCapacity
int currentCapacity =________________
StringBuilder.capacity();
____________ is 16 characters if created with
new StringBuilder().
Default capacity
When the capacity is exceeded, it expands
automatically using the formula:
_______________________________
New Capacity = (Old Capacity * 2) + 2
Default capacity is ___________ if created with
new StringBuilder().
16 characters
Unlike _______, which gives the actual number of
characters stored, capacity() tells how much
space is allocated.
length()
Unlike length(), which gives the _______________________, capacity() tells how much space is allocated.
actual number of
characters stored
Unlike length(), which gives the actual number of
characters stored, ___________ tells how much
space is allocated.
capacity()
Unlike length(), which gives the actual number of
characters stored, capacity() tells how much
___________________.
space is allocated
capacity()
Helps understand how much ______________________.
space is
allocated before resizing occurs
____________shows allocated storage space, not the
actual string length.
capacity()
capacity() shows__________________, not the
__________________.
allocated storage space
actual string length
______________→ Number of characters currently stored.
length()
Ensures that the StringBuilder has at least
minCapacity of storage, growing if necessary.
ensureCapacity(int minCapacity)
If __________ is greater than the _________________, the
capacity increases using the formula:
New Capacity = (Old Capacity * 2) + 2
minCapacity
current capacity
If minCapacity is greater than the current capacity, the
capacity increases using the formula:
____________________________
New Capacity = (Old Capacity * 2) + 2
If minCapacity is ________________ to the current
capacity, no change is made.
less than or equal
______________ → The minimum required capacity.
minCapacity
ensureCapacity()
This method does not ____________, only increases
it if necessary.
shrink capacity
ensureCapacity() only ____________________if necessary
– it does not decrease or shrink storage.
increases capacity
_____________ → Expands the storage if needed.
ensureCapacity()
Default capacity is 16, but it ___________ when
exceeded.
doubles plus 2
ensureCapacity():
Using a__________ can___________ when handling______________.
larger initial capacity
improve performance
large text data
Returns the number of characters in the
StringBuilder.
length()
_________________= StringBuilder.length();
int currentLength
int currentLength = _______________
StringBuilder.length();
_______→ Returns the actual number of
characters in the StringBuilder.
length()
The length changes dynamically as characters are
_______ or ________.
added
removed
Important for checking string size before performing
______________ like_______________.
operations
substring()
Returns the character at the specified
index
charAt(int index)
__________→ The position of the character to
retrieve.
index
Throws _____________ if
index is negative or greater than or equal to
length().
StringIndexOutOfBoundsException
charAt(int index):
Helps_____________ from the StringBuilder
retrieve a specific character
charAt(int index)
Key Takeaways
✔ charAt(int index) retrieves a specific character from
StringBuilder.
✔ _________________ – should be between 0 and length()
- 1.
✔ Throws____________________if the
index is out of range.
✔ Useful for ______________ – extracting characters,
checking initials, etc.
Validates the index
StringIndexOutOfBoundsException
processing strings
charAt(int index):
Useful for processing strings –______________,
________________, etc.
extracting characters
checking initials
Changes the character at the specified index to
the given char c.
setCharAt(int index, char c)
setCharAt(int index, char c)
Description: Changes the character at the specified index to
the given char c.
StringBuilder.setCharAt(int index, char c);
_______→ The position of the character to be replaced.
___→ The new character that will replace the existing
one at the_____.
This method modifies the _______ directly (inplace).
Throws StringIndexOutOfBoundsException if index is
negative or greater than or equal to length().
Usage: Useful for modifying ______________without modifying the whole string.
index
c
given index
StringBuilder
individual characters
______________ modifies a specific character directly in StringBuilder.
✔ _____________– must be between 0 and length()
- 1.
__________________ – capitalizing letters,
modifying punctuation, fixing typos, etc.
setCharAt(int index, char c)
Validates the index
Useful for text formatting
Returns a new String starting from start
index to the end.
substring(int start)
substring(int start)
Description: Returns a new String starting from start
index to the end.
______________ = StringBuilder.substring(int start);
______ → The index from which the substring begins
(inclusive).
________ (does not modify
StringBuilder).
Throws StringIndexOutOfBoundsException if
start is negative or greater than length().
String subStr
start
Returns a new String
___________ extracts part of the string starting
from start.
substring(int start)
substring(int start, int end)
Throws StringIndexOutOfBoundsException if:
start is _______.
end is _______________.
start is______________.
negative
greater than length()
greater than end
substring:
✔ Useful for extracting _____, _____, _____, ______
______, etc.
names
dates
words
file
extensions
Converts the StringBuilder data into a
String.
toString()
toString()
Description: Converts the StringBuilder data into a
String.
String str = ____________________
Returns a new String containing the same
sequence of characters as in StringBuilder.
Unlike StringBuilder, which is _______, String is
__________.
Useful when you need an immutable version of
the string, such as when returning the final result.
Usage: Since StringBuilder is mutable, this method is used when we need an immutable String representation.
StringBuilder.toString();
mutable
immutable
___________ converts StringBuilder into an immutable
String.
✔ Useful when the ____________ should not be modified.
✔ __________ (e.g., storing data, printing results)
often require String instead of StringBuilder.
✔ Does not modify the StringBuilder, just returns a ______.
toString()
final result
String operations
new String
____________ and ___________
have the same methods.
StringBuilder
StringBuffer
the keydifference is that StringBuffer is _____________ (synchronized) but ____________, while
StringBuilder is ___________ but not___________
threadsafe
slower
faster
threadsafe.
______________ does not use ___________,
making it more efficient in______________.
StringBuilder
synchronization
single-threaded environments
____________ uses _______ methods,
making it ____________.
StringBuffer
synchronized
thread-safe but slower
Since String is immutable, converting it
to StringBuffer or StringBuilder allows
__________.
modifications
Since StringBuffer and StringBuilder are
mutable, converting them to String gives an
_______________.
immutable version
Use StringBuffer and StringBuilder when
____________ are needed.
modifications
Use ________ to make strings immutable before
storing them.
toString()
In Java, working with different string types—String,
StringBuffer, and StringBuilder—is important for handling ______________.
text efficiently
