Strings And other things

Strings Overview The String Class and its methods The char data type and Character class StringBuilder, StringTokenizer classes Printf() method The StringBuffer class

What is a string A sequence of characters Representing alphanumeric data. Defined in the java.lang.String class String is a class and objects of String type are reference variables.

Making a string Declared as a typical object would be. String s= new String(“Hello”) Or using a short hand that java provides String s = “Hello”

The string class provides many methods. charAt(int idx) compareTo(string s) concat(string s) equals(string s) indexOf(int ch,int fromhere) lastIndexOf(int ch,int fromhere) length() replace(char old, char new) substring(int beginidx, int endidx) trim() toUpper(String s)

Joining strings Concatenation is the operation of joining one string on the end of another. S3 = S.concat(S2) Or S3 = S + S2 Java will implicitly type cast a numeric value as a string

String literals “Hello” “Good bye” “10,100” “576DSW” “ ” “Bill”

String equality String s1=“Hello” String s2=“Hello” If (s1==s2) System.out.print(“Equal”)  Not equal If (s1.equals(s2)) System.out.print(“Equal”)  Equal String s3=s1 If (s3==s1) System.out.print(“Equal”)  Equal

String comparisons If S1 < S2 may not work correctly If (S1.compareTo(s2)) < 0 System.out.print(“Less then”) If (S1.compareTo(s2)) == 0 System.out.print(“Equals”) If (S1.compareTo(s2)) > 0 System.out.print(“Greater then”)

Finding strings in strings indexOf(int ch,int fromhere) lastIndexOf(int ch,int fromhere) indexOf(String S, int fromhere) S1=“Hello” S1.indexof(‘l’)  Will return 2 S1.lastindexof(‘l’)  Will return 3

String Conversions String.valueof(number)  Returns a string And Integer.parseint(String)  Return a number

Converting Strings ToLowerCase() ToUppercase()

The stringbuffer class Like the string class Why 2 string classes? Other methods:.delete(int loc, int toloc).reverse().capacity() the size of the stringbuffer

Char data type A char is a single unicode value Unicode is a code used to specify character data. char c; char[] carray = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’ }; A character array can be used to build a string String s= new String(carray)

Command line arguments Command line arguments are passed to the args array in the main method. We can find the length of this array and process these arguments in our program.

That Character class A wrapper class  These are likes like Double and Integer which can be used in place of the primitive data types.  There is one for each primitive data type Provides methods like:  compareTo( char)  equals(char)  Character.isDigit(char) // a static method  Also: isLetter(char) and isLowerCase()…

StringBuilder An object that can be created to manipulate strings values mutably then store the result back into a string. Methods: append( String) insert(index, String) deleteCharAT( index) replace( startindex, endindex, string) toString()

StringTokenizer Used to break strings apart. This process is also known as parsing a string. A token is a special character used to delimit the parts of a string.  nextToken()  countTokens() The default token is set to “ \t\n\r\f” the white space characters. We can change this using the optional constructor..  StringTokenizer( string, tokenString)

Formatting data The printf() method of PrintStream class Format specifiers:  %.2f - a double value, 2 decimals  %d - an integer  %x- hexvalue System.out.printf(“data = %.2f”, data); Formatting dates:  %tA, %tB, %td, %tY  For day, month, dayof month, year

Argument index value System.out.printf(“%1$d, %2$.2f”, int, double) The 1$ and 2$ are used to specify the index of the parameter to use. By default the value of 1 is used. Field width: %3d- specifies the integer with room for 3 digits

Justification %-15s- left justify a string of 15 characters %15s- default right justify the string The format method  Formatter f = new Formatter()  F.format( “formatstring”, args…) Or  outstring =String.format( formatstring, args…)

Summary Strings Characters Char Format and sprint methods Importance of API documentation