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(min, max, absolute)  There 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 2 π Unit circle!

 The Math Class also contains two constants, PI and E Both are doubles Access both using Math.constantName Math.PI  f Math.E  f

 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)Log 10 (n)  pow(a,b)Exponent, or a b  sqrt(n)The square root of n

 There are also methods to round numbers 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  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 the angles of a triangle p123

 Distance Formula p124

 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 escape sequences \bbackspace \tTab \nLinefeed \fFormfeed \rCarriage 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)Returns true if ch is a digit isLetter(ch) Returns true if ch is a letter isLetterOrDigit(ch) Returns true if ch is a letter or a digit isLowerCase(ch) Returns true if ch is lowercase isUpperCase(ch) Returns true if ch is uppercase toLowerCase(ch) Returns the lowercase version of ch toUpperCase(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, s1 equal to s1 or >s1 compareToIgnoreCase(s1)Case insensitive verision of compareTo StartsWith(prefix)Returns true if the string starts with the prefix endsWith(suffix) Returns true if the strings ends with the suffix contains(s1)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 %bboolean value %ccharacter %ddecimal (integer) %f floating-point number %ea number in scientific notation %sa 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.