Transcript Mathematical Functions, Characters, and Strings

CS 201
California State University, Los
Angeles
 Various
Mathematical Functions
 Characters
 Strings
 We
have a lot of various mathematical
methods in Java
 We’ve covered 2 so far:
• Pow
 exponent method
• Random
 service method
 There
(min, max, absolute)
are also many trigonometric
methods
• We will cover…
 Similar
to pow, these methods are all in
the Math (java)Class
• Format is the same:
 Math.methodName
 Math.pow
 Math.sin
• Note: the Math Class is in the java.lang package,
and therefore doesn’t have to be imported
 Everything in java.lang is implicitly included in a Java
program
 sin(r)
Value of sine in radians
 cos(r)
Value of cosine in radians
 tan(r)
Value of tangent in radians
 toRadians(d) Convert degrees into radians
 toDegree(r) Convert radians into degrees
• (Note: “degree” is singular!)
 asin(a)
Angle (in radians) of inverse sine
 acos(a) Angle (in radians) of inverse cosine
 atan(a)
Angle (in radians) of inverse
tangent
 Keep
in mind most trig method
arguments are angles measured in
radians
 Remember the range of radians:
• 0 to 2π
• Unit circle!
 The
Math Class also contains two
constants, PI and E
• Both are doubles
• Access both using Math.constantName
• Math.PI
 3.14159265358979323846f
• Math.E
 2.7182818284590452354f
 Simply
methods that are related to
exponents:
• From the Math Class
 Math.methodName
 exp(n)
Raises the value of e to the power n
 log(n)
Natural Logarithm of n
 log10(n)
Log10(n)
 pow(a,b)
Exponent, or ab
 sqrt(n)
The square root of n
 There are also methods to round
• Again, from the Math Class
 Math.methodName
 ceil(x)
Ceiling of x
 floor(x) Floor of x
 rint(x) x rounded up to nearest integer
numbers
 If x is equally close to two integers, the even one is returned as
a double
 round(x)
rounds
 (int)Math.floor(x+0.5) for integers
 (long)Math.floor(x + 0.5) for doubles
 Note: For exactly halfway values (4.5), round(x) rounds up
(5), while rint(x) rounds down (4)
 Contains
min, max, abs, random
• min(a,b)
 Returns the minimum of both numbers
 Works for int, long, float, double
• max(a,b)
 Returns the maximum of both numbers
 Works for int, long, float, double
• abs(x)
 Returns the absolute value of x
 Works for int, long, float, double
 Range
review
 a + Math.random() * b
• Returns a random number between a and a+b,
excluding a+b
• How do I get a random number between 15 and
20?
• 400 – 4000?
 Compute
• p123
the angles of a triangle
 Distance
• p124
Formula
 We
can include (and process) characters
in Java!
• We use the char data type
• We use character literals to specify characters
 Type in a character between single quotes
• Characters are stored in UNICODE
 Way to store international characters
 Each number is matched to a character (in a
language)
 Was 16-bit, but that wasn’t enough space (!!!)
 Unicode
• International Characters
• Now holds up to 1,112,064 characters
 ASCII
 (American Standard Code for Information
Interchange)
 8-bit encoding scheme
 Used in most computers
 (Western characters)
 If
you don’t want to input characters with
string literals, you can use Unicode
values
• Takes 2 bytes (both in hex), preceded by \u
 \u03b1
 \u03b2
• Note: The first 128 values in Unicode are exactly
the same in ASCII, making the characters
compatible
 Between \u0000 and \u007F
 You
can use either ASCII or Unicode
• Ex:
 char letter = ‘A’;
 char letter = ‘\u0041’;
• Note: You can also use increment and decrement
to get the previous or next character!
 char a = ‘a’;
 ++a;
 System.out.println(a);
 If
you want to use special characters that
are used by the system, computer, or
Java, you must use escape sequences
• Ex: (quotes, tabs, backslashes)
• These represent the characters without actually
writing them
• Use the backslash and then a specific character
to specify
 Backslash (\) called an escape character
 Different
• \b
• \t
• \n
• \f
• \r
• \\
• \”
escape sequences
backspace
Tab
Linefeed
Formfeed
Carriage return
Backslash
Double quote
 You
can cast a char into a numeric type
• Only the lower 16-bits of data are used
 You
can cast a number into a char
• Converted to Unicode
• Floating-point values are cast to int first
 Numbers
between 0 and FFFF in hex are
implicitly casted into a char
• Anything else must be explicitly casted
 You
can compare characters using
relational operators
 Results are generated using Unicode
values
• What is the result of:
• ‘a’ < ‘b’ ?
• ‘1’ < ‘2’
 There
are different methods of testing
characters in the Character class
• isDigit(ch)
• isLetter(ch)
• isLetterOrDigit(ch)
•
•
•
•
a digit
isLowerCase(ch)
isUpperCase(ch)
toLowerCase(ch)
toUpperCase(ch)
Returns true if ch is a digit
Returns true if ch is a letter
Returns true if ch is a letter or
Returns true if ch is lowercase
Returns true if ch is uppercase
Returns the lowercase version of ch
Returns the uppercase version of ch
 Keep
in mind that char represents only one
character!
 If you want to store multiple characters (or a
string of characters) you need a String data
type
• Ex: String message = “Strings can store a lot more than char”;
• The String data type is a reference type (not a
primitive)
 Predefined class in Java (like System and Scanner)
 Any Java class can be used as a reference type for a
variable

The String class has its own methods.
• You can access these methods by using the dot (.)
operator
• Methods:
 length()
Returns the number of characters in the
string
 charAt(index) Returns the character at the index value
 concat(s1)
Returns a new string that concatenates the
current string with string s1
 toUpperCase() Returns a new string with all letters in
uppercase
 toLowerCase() Returns a new string with all letters in
lowercase
 trim()
Returns a new string with whitespace
(spaces) trimmed (removed) on both sides
 The
previous methods can only be used
after a string object has been created
(instantiantion)
• Methods are called instance methods
• Variable.methodName(arguments)
 The
Math methods can be used without
creating a Math class
• These methods are called static methods
• ClassName.methodName(arguments)
 String
Length
 Getting
Characters
 Concatenation
 Converting
Case
 You
can read in a String through console
in (Scanner)
• input.next();
 Reads in everything to a whitespace character
• nextLine()
 Reads in the entire line of text
• Important! Do not use nextLine() after
nextByte(), int, double, etc.
 To
read in a char, use nextLine(), then use
the method charAt(0); to return a
character

There are methods to Compare Strings:
• equals(s1) Returns true if the string is equal to s1
• equalsIgnoreCase(s1)
Case-insensitive version of equals
• compareTo(s1)
Returns an integer >0, =0, <0 if the string is >s1
• compareToIgnoreCase(s1)
Case insensitive verision of compareTo
equal to s1 or >s1
• StartsWith(prefix)
Returns true if the string starts with the prefix
• endsWith(suffix)
• contains(s1)
Returns true if the strings ends with the suffix
Returns true if s1 is a substring
 Note: You
may be tempted to use the
comparison operator (==) in order to
compare strings
• DO NOT DO THIS!!!!!!!
• Just checks if the strings are the same object!
 Do
not use relational operators(<,>,=,
etc) to compare strings!
 You
may need to get substrings from your
string
• Substrings = Strings within strings
• substring(beginIndex)
 Returns substring that begins with the character at
the index
 Note: The first index is 0
• substring(beginIndex, endIndex)
 Returns substring the begins with the character at
index, and ends at endIndex - 1

There are many different methods that find the position
(index) of a character or substring within a string
 These methods will return -1 if unmatched
 indexOf(ch)
Returns the index of the first occurrence of ch in the
string.
 indexOf(ch, fromIndex)
Returns the index of the first occurrence of ch
in the string after fromIndex.
 indexOf(s) Returns the index of the first occurrence of the string s1.
 indexOf(s, fromIndex)
Returns the index of the first occurrence of the
string s1.
 lastindexOf(ch)
Returns the index of the last occurrence of ch in the
string.
 lastindexOf(ch, fromIndex)
Returns the index of the last occurrence of ch
in the string after fromIndex.
 lastindexOf(s) Returns the index of the last occurrence of the string s1.
 lastindexOf(s, fromIndex)
Returns the index of the last occurrence of the
string s1.
 You
can convert a numeric string into a
number
• Use the Integer.parseInt() method
 From the Integer class
 Static method
• Can also use Double.parseDouble()
 Static method
 You
can use System.out.printf() to display
formatted output on the console
 Within the text use different format
specifiers
•
•
•
•
•
•
%b
%c
%d
%f
%e
%s
boolean value
character
decimal (integer)
floating-point number
a number in scientific notation
a string
 If
you put different variables in the printf,
append them after the string using
commas
• System.out.printf(“The Length is %d, area is
%f”,length, area);
 You
can format different precisions using
System.out.printf()
• P147
• Let’s do some examples!
 For character (c) and boolean (b)
• %[width]c
• %[width]b
• This separates out the number of spaces displayed in
the area. Value is displayed on the left
 Called the width
• Ex:
 %5c
 Specifies 5 spaces for the character. (Adds 4 spaces, then
displays the character
 %6b
 Specifies 6 spaces for the result (Adds 1 extra space for false, 2
spaces for true)
 For floating-point values:
• %[width].[number_of_decimals]f
• %[width].[number_of_decimals]e
• First number specifies the minimum width
• Next number specifies the number of decimals
shows
 Note: The decimal is included in the width!
• Ex: %5.2f
 Displays at least 5 spaces for width, and only 2 after
the decimal (if there are more digits left of the
decimal, they will be displayed
 For
integers and strings:
• %[width]d
• %[width]s
• Displays a minimum width for displaying
integers or strings
• If int or string is wider than minimum, it will
automatically expand.