Mastering Java Interfaces, Copying, Cloning, and Inner Classes

1. Air Force Institute of Technology Electrical and Computer Engineering Object-Oriented Programming in JavaTopic : Interfaces, Copying/Cloning, Inner Classes Maj Joel Young Joel.Young@afit.edu Maj Joel Young

2. Interface Concepts • Interface – a set of requirements for classes that want to conform to the interface • Interface is a promise that your class will implement certain methods with certain signatures • The way in which the methods is implemented is up to the class • Java's way of dealing with multiple inheritance • Inheritance restricted to one parent class • A class can implement any number of interfaces • For a class to implement an interface • Declare that the class intends to implement the given interface • Supply definitions for all methods in the interface

3. Interface Example public interface Comparable { int compareTo( Object other ); } class Employee implements Comparable { . . . public int compareTo( Object otherObject) { if (salary < other.salary) return –1; else if (salary > other.salary) return 1; else return 0; } }

4. Interface vs Abstract Class • Why not use abstract class? abstract class Comparable { public abstract int compareTo(Object other); } class Employee extends Comparable; • What if employee already extends another class? class Employee extends Person, Comparable // ERROR • But a class can implement multiple interfaces… class Employee extends Person implements Comparable, Cloneable

5. Properties of Interfaces • Can declare an object to be of an interface type Comparable empX = new Employee(…);Employee empY = new Employee(…);if (empX.compare(empY) < 0 ) … • Interfaces can be extended to create another interface, inheriting properties of the parent interface public interface MoreComparable extends Comparable • No instance fields or static methods in an interface • Constants can be specified in an interface public interface Powered extends Moveable{ double milesPerGallon(); double SPEED_LIMIT = 95;} • Implementing class must implement all methods of interface

6. Copying and Cloning

7. Shallow Copy

8. Deep Copy

9. Copying and Cloning in Java class Employee implements Cloneable { public Employee(String n, double s) { name = n; salary = s; } public Object clone() { try { // call Object.clone() Employee cloned = (Employee)super.clone(); // clone mutable fields cloned.payDay = (GregorianCalendar)payDay.clone(); return cloned; } catch (CloneNotSupportedException e) { return null; } } ... }

10. Inner Classes • A class that is defined inside another class • Has implicit reference to the outer class object that instantiated it -- this • Can access the implementation of the object that created it • Can be hidden from other classes in the same package • Can access local variables of scope in which they are defined • Why • Helper objects (e.g. property editor) • Can control private implementation of a class, without giving that access to other classes • Can have own state

11. Inner Classes class BankAccount { ... private double balance; // Inner Class private class InterestAdder implements ActionListener { ... public void actionPerformed(ActionEvent event) { // update interest double interest = balance * rate / 100; balance += interest; ... } private double rate; } }

12. Stack • A stack is a restricted form of a linked list. • Accessible only through the front of the list • LIFO: Last In, First Out. • Operators: • Insert: push • Remove: pop • The accessible element is called top.

13. Stack • Push 3, Push 5, Push 2, Pop Push: Pop: 3 5 2 Top 3 2 5 3 5 3

14. Stack Implementation Issues: • Which end is the top? • Where does “top” point to? • What is the cost of the operations?

15. Stack Implementation // Stack abstract class This could be an interface too abstract class Stack { // Reinitialize the stack abstract public void clear(); // Push an element onto the top of the stack abstract public boolean push( Object); // Remove the element at the top of the stack abstract public void pop( ); // Get the top element in the stack abstract public Object top( ); … // Array based implementation int size; // Maximum size of stack int top; // Index for top element Object[] stack; // Array holding elements }

16. Stack Implementation • Each stack operation take O(1) time. • Array implementation limited by declared size of the array. (Look at Vector in API)

17. Binary Search Tree • BST Property: All elements stored in the left subtree of a node with value K have values < K. All elements stored in the right subtree of a node with value K have values >= K.

18. Binary Search Tree Insert Insert: 15 12 8 9 root 12 8 15 9 • Go search for key until run off the end of the tree • Put new key there

19. Binary Search Tree Successor 17 15 14 13 root Successor(15): Successor(14): 17 12 15 12 8 7

20. Binary Search Tree Successor 17 15 13 root Delete(17) Delete(15) Delete(14) Successor(14.5) 12 Case I: Node is leaf. Just delete it. Case II: Node has only one child. Splice out the node 8 Case III: Node has two children. Delete successor of node and replace node’s key with successor’s key. Note that successor always satisfies Case I or Case II. 14.5 14 7 14.5 14

21. Homework • Look in API for things like Stack and List and Vector • Questions for COMACC • Feedback will come on your requirements specification