Expandable Vector

1. Expandable Vector Useful alternative to array, Useful especially when the size is uncertain

2. Difference from Array • Can store any number of elements into a vector • Can store only class instances in a vector • Provided in Java's util package Must include import java.util.* at the beginning of the file

3. Declaring and Using a Vector Variable Just as you declare other class variables Vector v = new Vector(); Add an element(instance of a class) m to the backend of a vector v.addElement(m); Add at a particular place: insertElementAt(m, index) v.insertElementAt(m, 0); //add to the front end, displacing others Remove from a particular place: deleteElementAt(m, index) v.deleteElementAt(0); //remove the first element, displacing others Read the element at the front end and the backend of a vector v.firstElementAt() v.lastElement()

4. Queue and Stack using Vector FIFO Queue • addElement(), firstElement(), deleteElementAt() LIFO Stack • insertElement(), firstElement(), deleteElementAt()

5. Retrieving and Replacing an Element Retrieve an element v.elementAt(index) Replace an element v.setElementAt(m, index) The size of a vector v.size()

6. Object Argument and Return Type public final Object elementAt(int index) { } public final void addElement(Object obj) { } Suppose the vector stores Movie instances (v.firstElement()).rating() // rating() is not defined in Object Typecasting ( (Movie) (v.firstElement())).rating() // rating() is not defined in Object

7. Object Argument Type All vector elements must be class instances. Then, how to make a vector of integers? ☞ Use a wrapper class Integer Integer i = new Integer(100); v.addElement(i); System.out.println("Value is " + i.intValue()); System.out.println("Value is " + i); String s = "120"; System.out.println("Value is " + Integer.valueOf(s)); There are other wrapper classes: Double ,Float ,Long

8. Enumeration int size = v.size(); for (index = 0; index < size; index++) { System.out.println( ((Movie) (v.firstElement())).rating()); }

9. Movie Example import java.io.*; import java.util.*; public class Demonstrate { public static void main(String argv[]) throws IOException { Vector mainVector = Auxiliaries.readData("input.data"); int counter; int size = mainVector.size(); for(counter = 0; counter < size; ++counter) { System.out.println( ((Movie)mainVector.elementAt(counter)).rating() ); } } }

10. Movie Example ( cont’ ) import java.io.*; import java.util.*; public class Auxiliaries { public static Vector readData(String fileName) throws IOException { FileInputStream inputFile = new FileInputStream(fileName); StreamTokenizer tokens = new StreamTokenizer(inputFile); Vector v = new Vector(); while(tokens.nextToken()!= tokens.TT.EOF) { int x = (int)tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; v.addElement(new Movie(x, y, z)); } inputFile.close(); return v; } }

11. String and StringBuffer Classes and Characters Strings are first-class citizens in Java, unlike in C or C++ where a string is a null-terminated array of characters. String class is for constant strings while StringBuffer class is for strings that will be modified.

12. Creation of Strings Creation of a string • Many strings are created from string literals "I am a boy" String s = "I am a boy" • Creation of a string object using a new keyword new String("I am a boy") String s = new String("I am a boy");

13. Access Methods of String Strings of type String are constants • Can concatenate two strings (+) to produce a new, longer string • Cannot add, delete, or change the characters in strings • To determine the length of a string, use string.length() • To extract a particular character from a string, use string.charAt(inde x) • To extract a position of a particular character, use indexOf(char) or lastIndexOf(char) • To extract a substring of a string, use substring()

14. Access Methods of String ( cont’ ) String extension() { int dot = filename.lastIndexOf('.'); return filename.substring(dot+1); } String path() { int sep = filename.lastIndexOf('/'); return filename.substring(0,sep); }

15. StringBuffer Class If the characters of a string will change, use a StringByffer class class ReverseString { public static String reverseIt (String src) { int len = src.length(); StringBuffer dest = new StringBuffer(len); for ( int i= (len-1); i >= 0; i--) { dest.append(src.charAt(i)); } return dest.toString(); } }

16. Access Methods of StringBuffer • To append a character at the end of a StringBuffer, use append() • To insert data (substring) in the middle of a StringBuffer, use insert() StringBuffer s = new StringBuffer("Drink Java"); s.insert(6, "Hot "); • To replace a character at a specific location, use setCharAt()

17. Converting Objects to Strings It is necessary and convenient to convert an object into a string All classes inherit toString method from the Object class and many classes in java.lang override it appropriately (e.g., all type wrapper classes override toString() for their string representation) Converting Strings to Numbers: String pi = "3.14159"; Float pi = Float.valueof(pi);

18. Example in the Textbook import java.io.*; import java.util.*; public class Demonstrate { public static void main(String argv[]) throws IOException { Vector mainVector; mainVector = Auxiliaries.readMixture("input.data"); int counter; int size = mainVector.size(); for (counter = 0; counter < size; ++counter) { System.out.println( ((Attraction)mainVector.elementAt(counter )).rating() ); } } }

19. Example in the Textbook ( cont’ ) import java.io.*; import java.util.*; public class Auxiliaries { public static Vector readMixture(String fileName) throws IOException { FileInputStream inputFile = new FileInputStream(fileName); StreamTokenizer tokens = new StreamTokenizer(inputFile); Vectore v = new Vector(); while(tokens.nextToken()!= tokens.TT.EOF) { String codeString = tokens.sval; tokens.nextToken(); int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval;

20. Example in the Textbook ( cont’ ) switch(codeString.charAt(0)) { case M : v.addElement(new Movie(x, y, z)); break; case S : v.addElement(new Symphony(x, y, z)); break; } } inputFile.close(); return v; } } ---------input.data--------- M 4 7 3 M 8 8 7 S 10 9 3

21. Advanced Features of Tokenizer Make a tokenizer to return a token for the end of a line • token_variable.eolIsSignificant(true); To know if the current token represents the end of a line • token_variable.nextToken() == token_variable.TT_EOL Make a tokenizer to use the double quotation mark to delimit strings with embedded spaces • token_variable.quoteChar(( in t) '"'); Character values can be used in switch statements • Because char is an integral type

22. Movie reading program import java.io.*; import java.util.*; public class Demonstrate { public static void main(String argv[]) throws IOException { Vector mainVector; mainVector = Auxiliaries.readMovieFile("input.data "); int counter; int size = mainVector.size(); for(counter = 0; counter < size; ++counter) { System.out.println( ((Movie)mainVector.elementAt(counter)).rating() ); } } }

23. Movie reading program ( cont’ ) import java.io.*; import java.util.*; public class Auxiliaries { public static Vector readMovieFile(String fileName) throws IOException { FileInputStream inputFile = new FileInputStream(fileName); StreamTokenizer tokens = new StreamTokenizer(inputFile); tokens.quoteChar((int) '"'); tokens.eolIsSignificant(true); Vector v = new Vector(); while(tokens.nextToken()!= tokens.TT.EOF) { String nameString = tokens.sval; tokens.nextToken(); int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval;

24. Movie reading program ( cont’ ) Movid m = (new Movid(x,y, z)); m.title = nameString; if (tokens.nextToken()== tokens.TT.EOL) { } else { m.poster= tokens.sval; tokens.nextToken(); } v.addElement(m); } inputFile.close(); return v; } } ----------input.data---------- “ABC KK" 4 7 3 "http://www.holywood.com/~abc" "DEF" 8 8 7