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Strings

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  1. Strings And other things

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

  3. 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.

  4. 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”

  5. 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)

  6. 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

  7. String literals • “Hello” • “Good bye” • “10,100” • “576DSW” • “700-6000” • “Bill”

  8. 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

  9. 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”)

  10. 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

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

  12. Converting Strings • ToLowerCase() • ToUppercase()

  13. 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

  14. 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)

  15. 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.

  16. 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()…

  17. 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()

  18. 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)

  19. 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

  20. 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

  21. 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…)

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

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