String Manipulation Chapter 15 This chapter explains the String facilities. You have already seen some of the main methods of the String class

Introduction: Strings are very important. All programming languages have primitive character manipulation Java has a useful collection of methods associated with Strings. This chapter reviews the features covered earlier in the text and extends the study of String processing methods

Some situations where Strings are used: Display messages on screen Input text from user Store data on files (see Chapter 17) Searching web pages Hold text for word processing and editors

Using Strings: a recap Declare variables and provide initial values –String x, y; –String myName = “Parr” –String myCountry = new String (“Japan”); ( new is performed implicitly and explicitly – it does not have to be used) Strings may be assigned to other Strings –String x = “England”; String y = “France”; y = x; y = “ “; // zero length String

The concatenation operator int number = 123; textField.setText (“ Value is “ + number ); Java rule: when one item is a string the others are converted to String –int value = 2333 – textField.setText ( “ value is “ + ( )); –// value is 55 - what is displayed in Text field Appending x + “ something” // adds to end of x

Compare Strings if ( x.equals (y)) …// the.equals operator is used with String (not = = ) Arrays of Strings – String [ ] cities = new String [10]; – cities[ 1 ] = “Los Angles”;

The characters within Strings Double quote surround String x = “abc”; To display a double quote use \ character textField.setText ( “ A \“tricky “ \“ problem!”); \n is the newline character \t is the tab charcater

A note about the class type char Holds one item as a 16 bit unicode character. Can be compared as swiftly as int – char initial = ‘M’; –// note single quotes – char marker = ‘\n’; // \n is a single character Character type rarely used but is efficient

The String class String class methods An exception StringIndexOutOfBounds –Index too large or negative –See page 228 screenshot of StringTemplate program User keys in the Strings, result field tells if they are equal …if ( string1.equals(string2)) result = “They are equal.”; – else result = “They are not equal.”; …

Comparing Strings Methods: – equals, equalsIgnoreCase, compareTo equals: if (string1.equals (string2)) result = “They are equal”; –equalsIgnoreCase: “This string” vs. “this string” –compareTo returns a result of: 0 = equal negative = object precedes positive object that follows positive = object follows – n = ant.compareTo (“bee”); // returns a negative number (ANSI value for b greater that a)

Amending Strings replace – string1 = “Massassappi”.replace ( ‘i’, ‘a’); Produces Mississippi toLowerCase – string1 = “Version 1.1” ; – result = string1.toLowerCase ( ); –Produces version toUpperCase – string1 = “Java”; – result = string1.toUpperCase; –Produces JAVA

trim – string1 = “ Center “; Result = string1.trim ( ); Produces “Center” without leading/following spaces

Examining Strings length returns current number of characters – string1.length returns characters in string1 –.length often used in loops with arrays Substrings: Extracts a specified part of a string – string1 = “position”; – result = string1.substring (2,5) ; –Result = sit // remember start count at zero

charAt – char c1, c2; –Returns the character at a specified position string1 = “position”; c1 = string1.charAt(1); // c1 = o // remember start at zero!

indexOf Is a substring contained within a String – int n = “mississippi”.index(“is”,4); Sets n to 4 // start count at zero if we tried (“is”, 5) N set to -1 // not found lastIndexOf –Return rightmost occurrence of substring – int place = “//a.b.c/directory/file.lastIndexOf(“/”); –Value 17 returned – again start your count at zero

endsWith Does String end with a particular substring? boolean r = “ (“/”); //sets r to true

StringTokenizer class If data has repeated substrings seperated by special characters splitting with stringTokenizer class more easily done January , 6,7,10,10,12,13, 15, 21, 20, 19,8 Separators are spaces after January and commas after each number

nextToken ( ) String example1 = “January 21 5”; String month, day, hours; stingTokenizer senddata = new StingTokenizer (example1, “ “); month = sumData.nextToken( ); day = sumData.nextToken( ); hours = sumData.nextToken( );

hasMoreTokens( ) Returns true if there are more data for nextToken to fetch import.util.*; // whenever StringTokenizer class to be used

String conversions Primitive types: int, double, boolean, character may be used int n = 123; String s = Integer.toString (n); // s becomes “123” double d = 12.34; String s = Double.toString (d); // s becomes “12.34”

parseInt n = Integer(SomeTextField.getText( )); –Converts a String into an int – d = Double.parseDouble (s);

String parameters String any = “Hello”; … return any + any –Method returns concatenated String HelloHello Example of String processing: String class has replace method – only handels a single character at a time. See method replace page 288. Replaces substring

private String replace (String original, String from, String to) { …

String case study 1970 Joseph Weizenbaum’s program ELIZA simulates psychiatrist –See page 289 User keys in a statement Program responds – echoes users statement – asks why? –Program Psychiatrist pages –Program AskFraiser pages –Screenshot page 291 –See Summary Strings page 294