Interfaces. Interfaces. Implementing Interfaces. Interfaces : : : :

Size: px

Start display at page:

Download "Interfaces. Interfaces. Implementing Interfaces. Interfaces : : : :"

Amelia Warner
6 years ago
Views:

Interfaces Interfaces The implementation of a module should be separated from its contractual interface and hidden from the clients of the module Contractual Interface Implementation is hidden from

1 Interfaces Interfaces The implementation of a module should be separated from its contractual interface and hidden from the clients of the module Contractual Interface Implementation is hidden from the clients Service Provider doaction1() doaction2() doaction3() doaction4() Interfaces Implementing Interfaces If the contractual interface is completely separated from the implementation, the contractual interface can exist on its own Contractual Interface No real implementations. doaction1() doaction2() doaction3() doaction4() In Java, the contractual interfaces are represented by interfaces. Class C1 implements X Interface X Class C2 implements X This is just a contractual interface. Class C3 implements X Interfaces will be implemented in real classes.

2 Class C4 implements X Implementing Interfaces Interface X behavior4() behavior5() Class C5 implements X Any classes implementing interface X, must implement (provide details of) all of the methods declared in the interface X. Those classes may have additional methods. Class C6 implements X behavior6() UML Notation for Interfaces X C1 C2 C3 Classes C1, C2, and C3 implement the interface X. Java Interfaces A class may implement more than one interface. (It can only extend one superclass.) Interfaces provide a mechanism for callbacks, like pointers to function in C++. An interface can extend another interface. Interfaces Example 1 public interface Nameable public void void setname(string s); s); public String getname(); public class WorkStation implements Nameable private String machinename; private User [] users; public void setname(string name) machinename = name; public String getname() return machinename;

Interfaces Example 1 public interface Nameable public void void setname(string s); s); public String getname(); public class Student implements Nameable private String name; private String id; Fields

3; public class C implements X public void setname(string name) this.

3 Interfaces Example 1 public interface Nameable public void void setname(string s); s); public String getname(); public class Student implements Nameable private String name; private String id; Fields in Interfaces If any fields (data members) are put in interfaces, they will automatically be static and final. The keywords static and final are optional. interface X double [] d = 0.0,0.1,0.2,0.3; public class C implements X public void setname(string name) this.name = name; public String getname() return name; public class TestInterfaceFields public static void main(string[] args) C c = new C(); for(int i=0;i<c.d.length;i++) System.out.println(c.d[i]); Example MyCollection Example MyCollection public interface MyCollection final int MAXIMUM = 100; public void push(object obj); public Object pop(); public String printcontent(); IN [0] [1] [2] OUT Create MyStack which is a collection of Object with a Last In First Out (LIFO) process. [3]

4 OUT Example MyCollection [0] [1] [2] [3] IN Create MyQueue which is a collection of Object with a First In First Out (FIFO) process. java.util.vector The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. However, the size of a Vector can grow or shrink as needed to accommodate adding and removing items after the Vector has been created. We will use java.util.vector class to store objects in our collection. java.util.vector Example MyQueue Constructor Vector(int initialcapacity) Constructs an empty vector with the specified initial capacity. v o void addelement(object o) iv do Object elementat(int index) i v d o void removeelementat(int index) i v d o int size() i d Adds the specified component to the end of this vector, increasing its size by one. Returns the component at the specified index Deletes the component at the specified index Returns the number of components in this vector

5 Example MyStack Example Using MyCollection public class UsingMyCollection public static void main(string[] args) System.out.println("===STACK==="); MyStack s = new MyStack(); createrandomintelements(s,5,0,10); s.printcontent(); System.out.println("Poping out"+s.pop()); s.printcontent(); System.out.println("Poping out"+s.pop()); s.printcontent(); System.out.println("Pushing in"+3); s.push(new Integer(3)); s.printcontent(); Example Using MyCollection Example Using MyCollection System.out.println("===QUEUE==="); MyQueue q = new MyQueue(); createrandomintelements(q,5,0,10); q.printcontent(); System.out.println("Poping out"+q.pop()); q.printcontent(); System.out.println("Poping out"+q.pop()); q.printcontent(); System.out.println("Pushing in"+3); q.push(new Integer(3)); q.printcontent(); public static void createrandomintelements (MyCollection c,int n,int min,int max) for(int i=0;i<n;i++) int randomint = (int)math.round(math.random()*(max-min)+min); c.push(new Integer(randomInt)); createrandomintelements() works with any classes implementing the MyCollection interface.

6 Single Vs. Multiple Inheritance Student not allowed in Java Employee inherit inherit Single Vs. Multiple Inheritance Interface Interface Student Employee float gpa float getgpa() no implementation implement implement float salary float getsalary() no implementation float gpa float salary float getgpa() float getsalary() getgpa() is implemented. getsalary() is implemented. StudentEmployee StudentEmployee getgpa() is implemented. getsalary() is implemented. Single Vs. Multiple Inheritance Interface Interface Student Employee implement implement FullTimeStudent FullTimeEmployee Student Re-use Advantage? getgpa() is implemented. Interface Student FullTimeStudent StudentEmployee inherit getgpa() is implemented. StudentEmployee getgpa() is implemented. getsalary() is implemented. getsalary() is implemented. Just inherits getgpa() from the superclass. getgpa() must be implemented. getgpa() must be implemented.

Delegation Design Pattern interface Student public

public float getsalary(); StudentImpl FullTimeStudent

EmployeeImpl FullTimeEmployee public class StudentImpl

getgpa() return gpa; public class EmployeeImpl

getsalary() return salary; public class FullTimeStudent

extends EmployeeImpl public class StudentEmployee

studentimpl = new StudentImpl(); private EmployeeImpl

7 Delegation Design Pattern interface Student public float getgpa(); Student Employee interface Employee public float getsalary(); StudentImpl FullTimeStudent UML Notation for association StudentEmployee EmployeeImpl FullTimeEmployee public class StudentImpl implements Student private float gpa; public float getgpa() return gpa; public class EmployeeImpl implements Employee private float salary; public float getsalary() return salary; public class FullTimeStudent extends StudentImpl public class FullTimeEmployee extends EmployeeImpl public class StudentEmployee implements Student, Employee private StudentImpl studentimpl = new StudentImpl(); private EmployeeImpl employeeimpl = new EmployeeImpl(); public float getgpa() return studentimpl.getgpa(); public float getsalary() return employeeimpl.getsalary(); Threads A Brief Overview The methods delegate the tasks to other objects.

8 Threads A thread is a single sequential flow of control within a program. A multi-threaded program has multiple threads (flows of control) running simultaneously. Most modern OS allows multiple threads to run on a single processor on a timesharing basis. Advantages of Multi-threaded Programs Applications are more responsive to the users. Monitoring User Interface allows a servers to handle multiple clients. takes advantage of multiple processors executing threads on different processors in parallel. Creation of Threads A thread is an instance of the Java.lang.Thread class. We make use of Java.lang.Thread in two ways 1 Extending Thread 2 Implementing Runnable Extending Thread The subclass MUST override run(). The run() method of a thread is invoked when execution starts. The execution of that thread ends when its run() method returns. Thread Runnable Thread t = new MyThread(); t.start(); creating an instance of MyThread MyThread MyThread starting the thread. run() of that instance of MyThread will be invoked automatically. Do not invoke run() directly.

$delay = delay; public void run() try while(true) System.out.println(i+"\t(By Thread ID = "+id+")"); i++; this.$ sleep(delay); catch(interruptedexception e) public static void main(string[] args) Thread t1 = new InfiniteCounter(1,1000); t1.start(); This This class class is is a program.

sleep(delay); catch(interruptedexception e) public static void main(string[] args) Thread t1 = new InfiniteCounter(1,1000); t1.start(); This This class class is is a program.

start(); no no excessive variable needed. Example InfiniteCounter Example InfiniteCounter Each output is 1000 milliseconds apart.

9 Example InfiniteCounter public class InfiniteCounter extends Thread int delay = 1000; int id; int i = 0; public InfiniteCounter(int id,int delay) this.id = id; this.delay = delay; public void run() try while(true) System.out.println(i+"\t(By Thread ID = "+id+")"); i++; this.sleep(delay); catch(interruptedexception e) public static void main(string[] args) Thread t1 = new InfiniteCounter(1,1000); t1.start(); This This class class is is a program. Create Create a new new instance of of InfiniteCounter. Example InfiniteCounter public class InfiniteCounter extends Thread int delay = 1000; int id; int i = 0; public InfiniteCounter(int id,int delay) this.id = id; this.delay = delay; public void run() try while(true) System.out.println(i+"\t(By Thread ID = "+id+")"); i++; this.sleep(delay); catch(interruptedexception e) public static void main(string[] args) new InfiniteCounter(1,1000).start(); no no excessive variable needed. Example InfiniteCounter Example InfiniteCounter Each output is 1000 milliseconds apart. public class InfiniteCounter extends Thread int delay = 1000; int id; int i = 0; public InfiniteCounter(int id,int delay) this.id = id; this.delay = delay; public void run() try while(true) System.out.println(i+"\t(By Thread ID = "+id+")"); i++; this.sleep(delay); catch(interruptedexception e) public static void main(string[] args) new InfiniteCounter(1,1000).start(); new InfiniteCounter(2,2000).start(); more more than than a single single thread thread

Example InfiniteCounter Thread and Applet Output from the first InfiniteCounter instance Output from the second InfiniteCounter instance What if we want to create a Java applet that also extends

Implementing Runnable Instead of creating a class that extends Thread, we create a class that implement the Runnable interface (which mean the class can still extend another class such as Applet).

10 Example InfiniteCounter Thread and Applet Output from the first InfiniteCounter instance Output from the second InfiniteCounter instance What if we want to create a Java applet that also extends Thread extends java.applet.applet extends Thread Recall that Java does not allow multiple inheritance. Implementing Runnable Instead of creating a class that extends Thread, we create a class that implement the Runnable interface (which mean the class can still extend another class such as Applet). Give the implementation of the run() method in the new class. When creating an instance of Thread, use the following constructor. public Thread(Runnable target) Animation Applets extending Applet while implementing Runnable This creates an instance of Thread whose run() method is overridden by the one in target.

11 Example DigitalClockApplet import java.awt.*; import java.util.calendar; import java.applet.applet; public class DigitalClockApplet extends Applet implements Runnable protected Thread mainthread; protected int delay; public void init() mainthread = null; delay = 200; public void start() if(mainthread==null) mainthread = new Thread(this); mainthread.start(); Example DigitalClockApplet repaint() forces the the applet to to paint the the screen by by invoking paint(). Do Do not not call call paint() directly. public void run() while(thread.currentthread() == mainthread) repaint(); try Thread.currentThread().sleep(delay); catch(interruptedexception e) Example DigitalClockApplet public void paint(graphics g) Dimension d = this.getsize(); Calendar c = Calendar.getInstance(); int h = c.get(calendar.hour_of_day); int m = c.get(calendar.minute); int s = c.get(calendar.second); g.setcolor(color.black); g.fillrect(0,0,d.width,d.height); g.setcolor(color.cyan); g.setfont(g.getfont().derivefont(50f)); g.drawstring(h+""+m+""+s,5,d.height/2); Concurrent Programming More to come later in the course Controlling Threads Communication among threads Thread Synchronization Thread Priority and Scheduling

CMSC 132: Object-Oriented Programming II. Inheritance

CMSC 132: Object-Oriented Programming II Inheritance 1 Mustang vs Model T Ford Mustang Ford Model T 2 Interior: Mustang vs Model T 3 Frame: Mustang vs Model T Mustang Model T 4 Compaq: old and new Price: