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Processing Data in Collections

Chapter 13. Processing Data in Collections. Object Wrappers. Collections can only hold objects. Primitive types ( int , double , float, etc.) are not objects. Primitives must be wrapped in special wrapper objects. Wrappers exist for each of the eight primitive types. What is an iterator?.

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Processing Data in Collections

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  1. Chapter 13 Processing Data in Collections

  2. Object Wrappers • Collections can only hold objects. • Primitive types (int, double, float,etc.) are not objects. • Primitives must be wrapped in special wrapper objects. • Wrappers exist for each of the eight primitive types.

  3. What is an iterator? • An iterator is an object that encapsulates the ability to iterate through or visit each element in the collection.

  4. Using the Iterator Interface • hasNext() method determines if there are more elements in the array • next() method returns the next element and advances the iterator

  5. The DrawShapes Application • User clicks in applet window to create one of three random shapes. • Each shape is added to a collection. • When user clicks in applet window, the collection is checked to see if a “hit” is registered on an existing shape. • When a “hit” occurs, the shape’s color will change randomly.

  6. The Shape Inheritance Hierarchy • Abstract class OurShape implements: • changeColorRandomly() to change the color of an object by randomly selecting a color • contains() to determine whether x, y coordinates of a mouse click fall within a shape’s boundaries • draw() to draw the shape at x, y coordinates specified by a mouse click

  7. Classes Derived from OurShape • OurRectangle • OurTriangle • OurCircle

  8. What is a linked list? • A LinkedList is a more powerful data structure that allows for quick and easy insertion and removal of elements.

  9. Linked Lists • LinkedLists come in two types: • Singly linked list—each node knows only the next node • Doubly linked list—each node knows both the previous and the next node

  10. What is a set? • A set is a collection with no duplicate elements. • Programmer needs to determine what constitutes a “duplicate.” • The equals() method can be used to provide an additional definition of equality.

  11. HashSet • Based on a hash table, a HashSet is a powerful data structure that can be used to retrieve objects quickly in a set. • Unordered collection • A hash code is used to organize objects in a HashSet

  12. TreeSet • TreeSet provides the properties of a set in a sorted collection. • Objects can be inserted in any order but are retrieved in sorted order • Uses Comparable interface to compare objects for sorting • Primitive types and String objects are comparable • Up to programmer to implement the compareTo() method for user-defined objects

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