CS411X - Lecture 13

Lecture Topic:

Command Line Interpreter in Java
Bugs in JDK 1.02
Finite State Diagram ( digraph )
Priority Queues ADT
Sample Quiz

Given a string, Run an applet => Command Line Interpreter

AppletFrame.java

// Generic AppletFrame
 
import java.awt.*;
import java.applet.Applet;
 
 
// Applet to Application Frame window
public class AppletFrame extends Frame {
 
    public static void startApplet(String className, String title, String args[]) {
        Applet a;
        Dimension appletSize;
 
        try {
            // create an instance of your applet class
            a = (Applet) Class.forName(className).newInstance();
        } catch (ClassNotFoundException e) {
            System.out.println("ClassNotFoundException in AppletFrame");
            return;
        } catch (InstantiationException e) {
            System.out.println("InstantiationException in AppletFrame");
            return;
        } catch (IllegalAccessException e) {
            System.out.println("IllegalAccessException in AppletFrame");
            return;
        }
 
        // initialize the applet
        a.init();
        a.start();
    
        // create new application frame window
        AppletFrame f = new AppletFrame(title);
    
        // add applet to frame window
        f.add("Center", a);
    
        // resize frame window to fit applet
        // assumes that the applet sets its own size
        // otherwise, you should set a specific size here.
        appletSize =  a.size();
        f.pack();
        f.resize(appletSize);
        f.resize(200,200);
 
        // show the window
        f.show();
    
    }  // end startApplet()
 
 
    // constructor needed to pass window title to class Frame
    public AppletFrame(String name) {
        // call java.awt.Frame(String) constructor
        super(name);
    }
 
    // needed to allow window close
    public boolean handleEvent(Event e) {
        // Window Destroy event
        if (e.id == Event.WINDOW_DESTROY) {
            dispose();
            return true;
        }
        
        // it's good form to let the super class look at any unhandled events
        return super.handleEvent(e);
 
    }  // end handleEvent()
 
}   // end class AppletFrame

rewriting code is not good idea, so AppletFrame now extends closable frame

// Applet to Application Frame window
public class ClosableFrame extends Frame {

    // constructor needed to pass window title to class Frame
    public ClosableFrame(String name) {
        // call java.awt.Frame(String) constructor
        super(name);
    }

    // needed to allow window close
    public boolean handleEvent(Event e) {
        // Window Destroy event
        if (e.id == Event.WINDOW_DESTROY) {
            dispose();
            return true;
        }
        
        // it's good form to let the super class look at any unhandled events
        return super.handleEvent(e);
 
    }  // end handleEvent()

}

This way, the Applet Frame need not concentrate on closing event as the parent frame

Closable Frame handles the Window destroy event. This is infact a neet idea.

Bugs in JDK 1.02

Save as

    FileDialog fd = new FileDialog(this ,"save as...", fileDialog.SAVE);
 
        fd.show( );
 
        String fn = fd.getFile( );
 
        if( fn != null ){
 
            if( fn.endswith(" *.* ")){
 
                  fn = fn.substring( 0, fn.length( ) - 4 );
 
                  String fqn = fd.getDirectory( ) + fn;
 
        ......

The above bug mentioned, is when a file is saved , it automatically

brings up *.* extension, with the file thereby resulting in a undefined

behaviour. This bug , we suppose is corrected in JDK 1.1

Parsing BTree

Finite state machine diagram is a directed graph ( diagraph )

An example class state can be defined as follows
class state{
 
      boolean flag = false;
 
      state left_child;
 
      state right_child;
 
      add_child_L(state S){
 
            left_child = S;
 
      }
 
      add_child_R(state S){
 
            right_child = S;
 
      }
 
      Array of states Ps[i]
 
      state stateArray[ ] = new state[10];
.......
An alternative definition of state class 
      class state{
 
            int LNext_state;
 
            int RNext_state;
 
            int x = getint( );
 
            int S = 0;
 
            S = stateArray[S].getNextsState(x);
 
            getNextState(int x){
 
                  if( x == 0 )
 
                       return LNext_state;
 
                  else
 
                       return RNext_state;
 
            }
.....

Priority Queue ADT

A priority Queue is base on the set model

Insert

Delete min - Return an element of lowest priority

Make null

Highest Priority gets lowest priority

Priority 40, 20, 26, 10, 45, 33, 14, 2

Left most leaf at Bottom level and move to Root

Delete O(log n)

Insert O(log n)

using an array A[i]

Left child at A[2i]

Right child at A[2i+1]

JGL - Java Generic Library

Sample Quiz

1. Methods in an interface are declared to be