Introduction to Programming G50PRO University of Nottingham Unit 10 : Strings

1. Introduction to ProgrammingG50PROUniversity of NottinghamUnit 10 : Strings Essam Eliwa http://www.cs.nott.ac.uk/~eoe eoe@cs.nott.ac.uk Room B49

2. Overview • Java String classes • The String Class • Example : StringDemo • Concatenating Strings • StringBuffer Class • Example : ReverseString • Converting Strings to Numbers • String valueOf Method http://www.cs.nott.ac.uk/~eoe

3. Java String classes • Two java classes that store and manipulate Strings: • String, for constant strings.(Java strings are immutable;  once a string object has a value, it cannot be changed) • StringBuffer, is like a String, but can be modified. http://www.cs.nott.ac.uk/~eoe

4. creating String and StringBuffer objects  : • String • String str = new String(“hello”); • String str = “hello”; • char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.'}; String helloString = new String(helloArray); • StringBuffer • StringBuffer dest = new StringBuffer();// Constructs a string buffer with no characters in it and an initial capacity of 16 characters. • StringBuffer dest = new StringBuffer(“hello”);// Constructs a string buffer initialized to hello Check Java API for all String and StringBuffer Constructors http://www.cs.nott.ac.uk/~eoe

5. The String Class • The String class is defined in the java.lang package (and isimplicitly imported by default) • Many helpful methods are defined in the String class such as • length() • equals(String) • toUpperCase() • toLowerCase() • indexOf(String) • subString(int begin) • subString(int begin, int end) • charAt(int index) http://www.cs.nott.ac.uk/~eoe

6. Example : StringDemo public class StringDemo { public static void main(String[] args) { String str = “HELLO"; int len = str.length(); char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an array of chars for (int i = 0; i < len; i++) { tempCharArray[i] = str.charAt(i); } // reverse array of chars for (int j = 0; j < len; j++) { charArray[j] = tempCharArray[len - 1 - j]; } String revStr = new String( charArray ); System.out.println(revSTR); }//end of main }//end of class http://www.cs.nott.ac.uk/~eoe

7. Concatenating Strings • The String class includes a method for concatenating two strings: • string1.concat(string2); //This returns a new string that is string1 with string2 added to it at the end. • Strings are more commonly concatenated with the + operator, as in: • String str = "Hello," + " world" + "!" // which sets str value to "Hello, world!" http://www.cs.nott.ac.uk/~eoe

8. StringBuffer Class • StringBuffer represents extendable and writable character sequences. • The main operations on a StringBuffer are the append and insert methods: • The append method always adds these characters at the end of the buffer • The insert method adds the characters at a specified point. http://www.cs.nott.ac.uk/~eoe

9. Example : ReverseString public class ReverseString {    public static String reverseIt( String source ) {      int len = source.length();       StringBuffer dest = new StringBuffer( len );      for ( int i = len - 1; i >= 0; i-- ) {         dest.append( source.charAt( i ) );       }       return dest.toString();    } // end method reverseIt } // end ReverseString http://www.cs.nott.ac.uk/~eoe

10. Converting Strings to Numbers • The String class itself does not provide any methods forconverting a String to numbers • Four of the "type wrapper" classes offer methods to convert a given String to a number • Integer • Double • Float • Long String str = “5.12”; float a = (Float.valueOf( str ) ).floatValue(); int i = Integer.parseInt( str ); http://www.cs.nott.ac.uk/~eoe

11. String valueOf Method • String class offers valueOf() methods which converts between various types to String boolean result = true;int in = 234;double dou = 34.86;float flt = 54.889f;System.out.println("boolean value:“ + String.valueOf(result)        + "\ninteger value: " + String.valueOf(in)        + "\ndouble value: " + String.valueOf(dou)        + "\nfloat value: " + String.valueOf(flt)); http://www.cs.nott.ac.uk/~eoe

12. Summary • Java String classes • The String Class • Example : StringDemo • Concatenating Strings • StringBuffer Class • Example : ReverseString • Converting Strings to Numbers • String valueOf Method http://www.cs.nott.ac.uk/~eoe