Character and string Methods Flashcards
A ___________ is not a simple data type but a reference—it holds a memory address, not the actual
value.
String variable
A String variable is _____________ but a reference—it holds a memory address, not the actual
value.
not a simple data type
A String variable is not a simple data type but a _________—it holds a memory address, not the actual
value.
reference
A String variable is not a simple data type but a reference—it holds a _____________, not the___________.
memory address
actual value
When you use __ to compare two
Strings, you’re comparing their _____________, not their ________.
==
memory addresses
actual values
_________ usually want to compare the values
of Strings, not their memory addresses.
Programmers
Programmers usually want to compare the ___________, not their___________.
values of Strings
memory addresses
______________:
Holds a single character
Character Class
Character Class:
Holds a _________
single character
______________:
Provides methods to manipulate and inspect
single-character data.
Character Class
Character Class:
Holds a single character (e.g., ‘A’, ‘8’, ‘$’).
Provides methods to ________ and ______________.
manipulate
inspect single-character data
___________:
Used for fixed (unchanging) text data made
up of one or more characters.
Offers many methods to simplify working with
Strings.
String Class
String Class:
Used for_______________ made
up of _______________.
Offers many methods to simplify working with
Strings.
fixed (unchanging) text data
one or more characters
The _____________:
Used to store a single character, such as a
letter, digit, or punctuation mark.
char Data Type
The char Data Type:
Used to _____________, such as a
letter, digit, or punctuation mark.
store a single character
The char Data Type:
Used to store a single character, such as a
_______,________, or_____________.
letter
digit
punctuation mark
char literals are written inside_______________
single quotation
marks
Since char is a _____________, it holds
actual values (not memory addresses).
primitive data type
Since char is a primitive data type, it holds
___________ (_________).
actual values
not memory addresses
You can compare char values using _______________ like == and >.
relational operators
Comparisons are based on the ________ value of
each character.
Unicode
These comparisons work as you’d expect—
_____________.
alphabetically
Java also provides a _________ for working
with characters.
Character class
This class includes useful methods for_______ and
__________ character values.
testing
manipulating
This __________ includes useful methods for testing and
manipulating character values.
class
The ____________ is part of the____________, which is automatically imported into
every Java program.
Character class
java.lang package
Checks if the given character is a letter
(uppercase or lowercase).
isLetter(char ch)
Checks if the given character is a digit
isDigit(char ch)
Checks if the given character is a
whitespace (space, tab, newline, etc.).
isWhitespace(char ch)
Converts the given character to its
uppercase equivalent.
toUpperCase(char ch)
Converts the given character to its
lowercase equivalent.
toLowerCase(char ch)
Checks if the given character is an
uppercase letter.
isUpperCase(char ch)
Checks if the given character is a
lowercase letter.
isLowerCase(char ch)
Converts the given character to a
String.
toString(char ch)
Checks if the given character is a letter
or a digit.
isLetterOrDigit(char ch)
Compares two characters numerically
based on their Unicode values.
compare(char x, char y)
Compares two characters numerically based on their _______________.
Unicode values
_____________ are one of the most common
dataType in Java.
Strings
Strings are one of the most common
______ in Java.
dataType
Primitive Types (e.g., int):
When you declare int x = 10;, the __________ of x
holds the value 10.
If you update x to 45, the _____ replaces the old
one at the same memory address.
memory address
new value
When you declare String aGreeting = “Hello”;,
aGreeting holds the ____________ of the String “Hello”, not the ________.
memory address
actual characters
You cannot choose _________; they are assigned by the
__________.
memory addresses
operating system
Strings are ____________they are never
changed. Instead, new Strings are
created, and references are updated to
point to the new memory addresses.
immutable
Strings are immutable—they are never
changed. Instead, ________ are
created, and _________ are updated to
point to the ______________.
new Strings
references
new memory addresses
Comparing Strings with < or > will cause a ________________. These operators cannot be used with Strings.
compilation error
Use the + operator to combine (concatenate) Strings.
Concatenating Strings
Created using double quotes with no characters
inside.
Empty Strings
Refers to a memory address where no characters are
stored.
Empty String
Refers to a_________ where _________ are
stored.
Can be used with String methods like ________.
memory address
no characters
.equals()
_________:
Created by assigning null to a String.
Null Strings
A _________ does not reference any memory address.
null String
Cannot be used with String methods like___________
—it will cause an error.
.equals()
Others find it ________ since unassigned Strings are
null by default.
redundant
Returns the number of characters in a String.
length()
Finds the position of a character or substring in a String.
indexOf()
Returns the character at a specific position.
charAt()
Extracts part of a String.
substring()
The __________ method takes_______________—a start position and an end position—that are both based on the fact that a String’s first position is position zero.
substring()
two integer arguments
The_________________ is the difference between the second integer and the first integer; if you call the method without a second integer argument, the substring extends to the end of the original string.
length of the extracted substring
The length of the extracted substring is the difference between the _________________; if you call the method without a second integer argument, the substring extends to the end of the original string.
second integer and the first integer
Checks if a String starts with a specific substring.
startsWith()
Checks if a String ends with a specific substring
endsWith()
Replaces all occurrences of a character or String/substring.
replace()
Checks if a String contains a specific substring.
contains()
Converts current dataType to a String (implicitly used in print() and println()).
toString()
Finds the position of a substring starting from a specific index.
indexOf(String, int)
Checks if a String is empty or contains only whitespace.
isBlank()
Checks if a String has no characters.
isEmpty()
Converts the String to lowercase.
toLowerCase()
Converts the String to uppercase.
toUpperCase()
Removes leading and trailing whitespace.
strip()
Removes leading and trailing whitespace (similar to strip() but available in older Java versions).
trim()
Why Convert Strings to Numbers?
perform arithmetic operations.
It provides the _______________ method,
which takes a String and returns its integer value.
parseInt()
parseInt() is a static method, so you call it using the class name (___________).
Integer.parseInt()
It provides the ___________method, which takes a
String and returns its double values.
parseDouble()
indexOf(): Finds the position of a character or substring
in a String. Returns ______ if not found.
-1
Converts a String to a float.
Float.parseFloat():
Converts a String to a long.
Long.parseLong()
Forgetting to handle null Strings, leading to ____________.
runtime errors
Misusing methods like charAt() with invalid positions (causing ______________________).
StringIndexOutOfBoundsException
