Chapter 4.4 Strings Flashcards
Define a string
A string is a sequence of characters.
A string value is enclosed in matching double quotes (“).
Strings are known as a ___ type not an ___
The String type is not a primitive type. It is known as a reference type. Any Java class can be used as a reference type for a variable.
Strings must be surrounded by ___
and they contain most characters except:
- Must be surrounded double quotes.
String literals (values) have the quotation marks removed when displayed.
- Strings can contain most characters except enter, backspace, tab, and backslash.
These characters must be escaped by using an escape sequence which consists of the escape character () followed by a character or a combination of digits.
Strings can have up to ___ characters
Potentially up to 2,147,483,647 characters is allowed.
The minimum number of characters is zero “”, which is called the empty string.
Backspace
Escape sequence:
Unicode:
Decimal value:
\b
\u0008
8
Tab
Escape sequence:
Unicode:
Decimal value:
\t
\u0009
9
Linefeed
Escape sequence:
Unicode:
Decimal value:
\n
\u000C
10
Formfeed
Escape sequence:
Unicode:
Decimal value:
\f
\u000C
12
Carriage return
Escape sequence:
Unicode:
Decimal value:
\r
\u000D
13
Backlash
Escape sequence:
Unicode:
Decimal value:
\u005C
92
Double quote:
Escape sequence:
Unicode:
Decimal value:
"
\u0022
34
Syntax for a simple method for String objects
referenceVariable.methodName(arguments)
ex:
String message = “Welcome to Java”;
System.out.println(“The length of “ + message + “ is “ +message.length());
What is the String method to return the number of characters in the String
length() or length() - 1
What is the String method to return the character at the specified index from this string
charAt(index)
The charAt(index) method can be used to retrieve a specific character in a string s,
where the index is between 0 and length()–1.
What is the String method to return a new String that concatenates
concat(s1)
What is the String method to return a new string with all letters uppercase
What is the String method to return a new string with all letters lowercase
toUpperCase()
toLowerCase()
What is the String method to return a new string with whitespace characters trimmed on both sides
trim()
Java uses the + operator for both addition and concatenation.
If one of the operands is a nonstring (e.g., an integer), the nonstring value is converted into a string and concatenated with the other string.
If neither of the operands is a string, the plus sign (+) is the addition operator that adds two numbers.
Reading a String from the console
To read a string from the console, invoke the next() method on a Scanner object.
The next() method reads a string that ends with a whitespace character.
Scanner input = new Scanner(System.in);
System.out.print(“Enter three words separated by spaces: “);
String s1 = input.next();
String s2 = input.next();
String s3 = input.next();
System.out.println(“s1 is “ + s1);
System.out.println(“s2 is “ + s2);
System.out.println(“s3 is “ + s3);
You can use the ___ method to read an entire line of text.
You can use the nextLine() method to read an entire line of text. The nextLine() method reads a string that ends with the Enter key pressed.
Scanner input = new Scanner(System.in);
System.out.println(“Enter a line: “);
String s = input.nextLine();
System.out.println(“The line entered is “ + s);
Note:
To avoid input errors, be cautious using line-based input after a token-based input in theprogram.
Comparing Strings: returns true if this String is equal to string s1
equals(s1)
Comparing Strings: returns true if this string is equal to string s1
equalsIgnoreCase(s1)
Return an integer greater than 0, equal to 0, or less than 0 to indicate whether this string is greater than, equal to, or less than s1
compareTo(s1)
Same to compareTo except that the comparison is case sensitive
compareToIgnoreCase(s1)
Returns true if this String starts with the specified prefix
startsWith(prefix)
Returns true if this string ends with the specified suffix
endWith(suffix)
Returns this substring that begins with the character at the specified beginIndex and extends to the end of the string
substring(beginindex)
Returns this String’s substring that begins at the specified beginIndex and extends to the character at the endIndex is not part of the substring
substring(beginIndex, endIndex)
Returns the index of the of the first occurrence of the ch in the string
indexOf(ch)
Returns the index of the first occurrence of ch after fromIndex in the String, Returns -1 if not matched
indexOf(ch, fromIndex)
Returns the index of the first occurrence of the of string s in the String. Returns -1 if not matched
indexOf(s)
Returns the index of the first occurrence of String s in this string after fromIndex. Returns true if not matched.
indexOf(s, fromIndex)
Returns the index of the last occurrence of ch in the String. Returns -1 if not matched.
lastIndexOf(ch)
Returns the index of the last of the last occurrence of ch before fromIndex in this string. Return -1 if not matched.
lastIndexOf(ch, fromIndex)
Return the index of the last occurrence of string s. Returns -1 if not matched.
lastIndexOf(s)
Returns the index of the last occurrence of string s before fromIndex. Returns -1 if not matched.
lastIndexOf(s, fromIndex)
To convert a string into an int value, use the ___ method:
To convert a string into an int value, use the Integer.parseInt method:
int intValue = Integer.parseInt(intString);
To convert a string into a double value, use the ___ method:
To convert a string into a double value, use the Double.parseDouble method:
double doubleValue = Double.parseDouble(doubleString);
If the string is not a numeric string, conversion would cause a runtime error.
To convert a number into a string use the string concatenating operator as follows:
To convert a number into a string use the string concatenating operator as follows:
String str = intValue + “ “ + doubleValue;
Formatting output: how to display numbers in a certain format (Strings)
Often, it is desirable to display numbers in a certain format. To do that we can use the printf statement:
System.out.printf(format, items);
Where format is a string that may consist of substrings and format specifiers.
What type does an item have to be to format output
- An item may be a numeric value, character, boolean value, or a string.
What does a format specifier specifier do
A format specifier specifies how an item should be displayed.
How to format output
Each specifier begins with a percent sign (%).
To output a literal % in the format string, use %%
Items must match the format specifiers in order, in number, and in exact type.
You can specify the field width and precision in a format specifier.
By default, the output is right justified. You can put the minus sign (−) in the format specifier to specify that the item is left justified in the output within the specified field.
%b output and example
boolean
T or F
%c output and example
a character
‘a’
%d output and example
a decimal integer
200
%f output and example
a floating point number
45.46000
%e output and example
a number in standard scientific notation
4.556000e+01
format syntax
1.2f
1 = field width
2 = precision
f = conversion code
Character method to: return the lowercase of the specified character
Math.pow(a, b)
