Mastering Vectors in Java Programming

1. Vectors, Strings, and Enumeration Data Types Chris Kiekintveld CS 2401 (Fall 2010) Elementary Data Structures and Algorithms

2. A Weakness of Arrays • Suppose we declare an array of “Student” objects: Student[] students = new Student[10]; • What if a new student joins the class? • The size of an array cannot be increased after it is instantiated Java Programming: Program Design Including Data Structures

3. Resizing an Array (the hard way) Student[] students = new Student[10]; // do some stuff… // now we need to add student 11 Student[] students2 = new Student[11]; for(int i = 0; i < students.length; i++) { students2[i] = students[i]; } student[10] = new Student(); Java Programming: Program Design Including Data Structures

4. classVector • The classVector can be used to implement a list, replacing a simple array • The size of a Vector object can grow/shrink during program execution • The Vector will automatically grow to accommodate the number of elements you put in it Java Programming: Program Design Including Data Structures

5. classVector (continued) • The classVector is contained in the package java.util • Programs must include either: • import java.util.*; • import java.util.Vector; Java Programming: Program Design Including Data Structures

6. Vector Declaration • Declare/initialize Vector<Student> students = new Vector<Student>(); • The syntax <…> is used to declare the type of object that will be stored in the Vector • If you add a different type of object, an exception is thrown • Not strictly necessary, but highly recommended (compiler warning) Java Programming: Program Design Including Data Structures

7. Vector Size/Capacity • The size of a vector is the number of elements • The capacity of a vector is the maximum number of elements before more memory is needed • If size exceeds capacity when adding an element, the capacity is automatically increased • Declares a larger storage array • Copies existing elements, if necessary • Growing the capacity is expensive! • By default, the capacity doubles each time Java Programming: Program Design Including Data Structures

8. Setting Initial Capacity • If you know you will need a large vector, it may be faster to set the initial capacity to something large Vector<Student> students = new Vector<Student>(1000); Java Programming: Program Design Including Data Structures

9. Size and capacity • Get the current size and capacity: Vector<Student> students = new Vector<Student>(1000); students.size(); // returns 0 students.capacity(); // returns 1000 • Setting size and capacity: // adds null elements or deletes elements if necessary students.setSize(10); // increases capacity if necessary students.ensureCapacity(10000); Java Programming: Program Design Including Data Structures

10. Adding Elements Vector<String> stringList = new Vector<String>(); stringList.add("Spring"); stringList.add("Summer"); stringList.addElement("Fall"); stringList.addElement("Winter"); add and addElement have identical functionality Java Programming: Program Design Including Data Structures

11. Accessing Elements stringList.get(0); // “Spring” stringList.get(3); // “Winter” stringList.get(4); // ArrayIndexOutOfBounds Exception Java Programming: Program Design Including Data Structures

12. Primitive Data Types and the class Vector • Every component of a Vector object is a reference • Primitive data types are not objects • Corresponding to each primitive data type, Java provides a wrapper class • JDK 5.0 provides autoboxing and auto-unboxing of primitive data types Java Programming: Program Design Including Data Structures

13. Primitive Data Types and the class Vector (continued) • Creating a Vector of Integer objects Vector<Integer> list = new Vector<Integer>(); list.add(13); // with autoboxing list.add(new Integer(25)); // without autoboxing int tmp = list.get(0); // with autounboxing int tmp2 = list.get(0).intValue() //without Java Programming: Program Design Including Data Structures

14. Vector and the foreach loop • Each Vector object is a collection of elements • You can use a foreach loop to process its elements • Exactly like using a foreach loop with an array • Syntax: for (type identifier : vectorObject) statements Java Programming: Program Design Including Data Structures

15. Members of the classVector Java Programming: Program Design Including Data Structures

16. Members of the classVector (continued) Java Programming: Program Design Including Data Structures

17. Members of the classVector (continued) Java Programming: Program Design Including Data Structures

18. Members of the classVector (continued) Java Programming: Program Design Including Data Structures

19. Vectors, Strings, and Enumeration Data Types(continued) Chris Kiekintveld CS 2401 (Fall 2010) Elementary Data Structures and Algorithms

20. Exercise Vector<Integer> a = new Vector<Integer>(); a.add(4); a.add(7); a.add(10); a.set(1, 5); int tmp = a.remove(0); System.out.println(tmp); System.out.println(a.indexOf(new Integer(10)); System.out.println(a.toString()); a.clear(); System.out.println(a.isEmpty()); Java Programming: Program Design Including Data Structures

21. Multi-dimensional Vectors • Can we have a 2d vector? Yes! • Just like a 2d array, but notation is more cumbersome Java Programming: Program Design Including Data Structures

22. Multi-dimensional Vectors Vector<Vector<Integer>> a = new Vector<Vector<Integer>>(); for (int i = 0; i < 4; i++) { Vector<Integer> tmp = new Vector<Integer>(); for (int j = 0; j < 4; j++) { tmp.add(i+j); } a.add(tmp); } System.out.println(a.get(2).get(3)); System.out.println(a.get(0).get(2)); Java Programming: Program Design Including Data Structures

23. Vector vs. ArrayList • Java has another class called ArrayList • This class is almost identical in function to Vector, and has most of the same methods • ArrayList is typically faster • ArrayList should *not* be used if your code is multi-threaded (i.e., if you allow parallel execution) Java Programming: Program Design Including Data Structures

24. Enumeration Types • Enumeration or enum types • User-defined data types • User specifies the values of that data type • Defined using the key word enum • Syntax example: • enum Grades {A, B, C, D, F}; • The values are identifiers • Called enumeration or enum constants • Must be unique within an enum type Java Programming: Program Design Including Data Structures

25. Enumeration Types (continued) • Each enum type is a special type of class • Values are (special types of) objects of that class • Using an enum type Grades myGrade; myGrade = Grades.B; System.out.println (“myGrade: ” + myGrade); • Each enum constant has an ordinal value • Ordinal value of the first enum constant is 0 Java Programming: Program Design Including Data Structures

26. Enumeration Types (continued) Java Programming: Program Design Including Data Structures

27. Enumeration Types (continued) • Because each enum type is a class, it can contain • Constructors, (private) data members, and methods • enum type considerations • Defined using enum rather than class • enum types are implicitly final • enum constants are implicitly static • You cannot instantiate objects using the operator new • Constructors are implicitly private • You cannot create new classes from an enum type Java Programming: Program Design Including Data Structures

28. Enumeration Types (continued) Java Programming: Program Design Including Data Structures

29. public enum Directions{North, South, East, West}; public int xPos = 0; public int yPos = 0; public void move(Directions dir) { switch(dir) { case Directions.North: yPos++; break; case Directions.South: yPos--; break; case Directions.East: xPos++; break; case Directions.West: xPos--; break; case default: System.out.println(“Invalid direction!”); } } Java Programming: Program Design Including Data Structures

30. Enumeration Types • See this site for more discussion and examples: http://download.oracle.com/javase/1.5.0/docs/guide/language/enums.html Java Programming: Program Design Including Data Structures

31. Strings • Strings are essentially arrays of characters • The string class provides many functions for manipulating strings • Searching/matching operations • Replacing characters • Finding characters • Trimming whitespace • Etc. Java Programming: Program Design Including Data Structures

32. class String (Revisited) Java Programming: Program Design Including Data Structures

33. class String (Revisited) (continued) Java Programming: Program Design Including Data Structures

34. class String (Revisited) (continued) Java Programming: Program Design Including Data Structures

35. class String (Revisited) (continued) Java Programming: Program Design Including Data Structures