有一個(gè)簡單的工具來繪制基本的幾何形狀。該Java開發(fā)工具是使用 AWT 組件編寫的，并詳細(xì)闡述了諸如內(nèi)部類、事件處理、多態(tài)性和菜單處理等功能。在本文中，我們將逐塊逐步執(zhí)行代碼以構(gòu)建我們的簡單繪圖工具。

第 1 步：空的類結(jié)構(gòu)

首先，我們從一個(gè)空的類結(jié)構(gòu)開始，我們從 java.awt.Frame 類擴(kuò)展/繼承它。我們設(shè)置框架的標(biāo)題和大小并使其可見。

//Title:        A Simple Drawing Tool
//Version:      1.0
//Copyright:    Copyright (c) 2001
//Author:       Yasir Feroze Minhas
//Company:      KAPS Computing (pvt) Ltd.
//Description:  This is a simple tool written using AWT for drawing basic shapes.
package graph;
import java.awt.*;
public class SimpleDrawingTool extends Frame{
  public SimpleDrawingTool() {
    //set frame's title
    super("Simple Drawing Tool");
    //set frame size
    this.setSize(400, 400);
    //make this frame visible
    this.setVisible(true);
  }
  public static void main(String[] args) {
    SimpleDrawingTool simpleDrawingTool = new SimpleDrawingTool();
  }
}

第 2 步：添加菜單

接下來，我們將菜單欄附加到我們的繪圖工具，并用最少的菜單項(xiàng)對其進(jìn)行裝飾。

//Title:        A Simple Drawing Tool
//Version:      1.0
//Copyright:    Copyright (c) 2001
//Author:       Yasir Feroze Minhas
//Company:      KAPS Computing (pvt) Ltd.
//Description:  This is a simple tool written using AWT for drawing basic shapes.
package graph;
import java.awt.*;
public class SimpleDrawingTool extends Frame{
  //constants for menu shortcuts
  private static final int kControlA = 65;
  private static final int kControlD = 68;
  private static final int kControlC = 67;
  private static final int kControlR = 82;
  private static final int kControlP = 80;
  private static final int kControlT = 84;
  private static final int kControlX = 88; 
  public SimpleDrawingTool() {
    //set frame's title
    super("Simple Drawing Tool");
    //add menu
    addMenu();
    //set frame size
    this.setSize(400, 400);
    //make this frame visible
    this.setVisible(true);
  }
  public static void main(String[] args) {
    SimpleDrawingTool simpleDrawingTool = new SimpleDrawingTool();
  }
  /**
  This method creates menu bar and menu items and then attach the menu bar
  with the frame of this drawing tool.
  */
  private void addMenu()
  {
    //Add menu bar to our frame
    MenuBar menuBar = new MenuBar();
    Menu file = new Menu("File");
    Menu shape = new Menu("Shapes");
    Menu about = new Menu("About");
    //now add menu items to these Menu objects
    file.add(new MenuItem("Exit", new MenuShortcut(kControlX)));
    shape.add(new MenuItem("Rectangle", new MenuShortcut(kControlR)));
    shape.add(new MenuItem("Circle", new MenuShortcut(kControlC)));
    shape.add(new MenuItem("Triangle", new MenuShortcut(kControlT)));
    shape.add(new MenuItem("Polygon", new MenuShortcut(kControlP)));
    shape.add(new MenuItem("Draw Polygon", new MenuShortcut(kControlD)));
    about.add(new MenuItem("About", new MenuShortcut(kControlA)));
    //add menus to menubar
    menuBar.add(file);
    menuBar.add(shape);
    menuBar.add(about);
    //menuBar.setVisible(true);
    if(null == this.getMenuBar())
    {
      this.setMenuBar(menuBar);
    }
  }//addMenu()
}

第 3 步：添加事件處理程序

菜單欄就位，您可以導(dǎo)航不同的菜單和菜單項(xiàng)。但由于它們尚未附加任何事件處理程序，因此您只能做導(dǎo)航。下一步是添加事件處理程序，以便我們可以捕獲用戶的選擇并采取相應(yīng)的行動(dòng)。

package graph;
import java.awt.*;
//import event package
import java.awt.event.*;
//import swing package for pop up message box
import javax.swing.*;
public class SimpleDrawingTool extends Frame{
  ...
  private void addMenu()
  {
    ...
    file.add(new MenuItem("Exit", new MenuShortcut(kControlX))).addActionListener(new WindowHandler());
    shape.add(new MenuItem("Rectangle", new MenuShortcut(kControlR))).addActionListener(new WindowHandler());
    shape.add(new MenuItem("Circle", new MenuShortcut(kControlC))).addActionListener(new WindowHandler());
    shape.add(new MenuItem("Triangle", new MenuShortcut(kControlT))).addActionListener(new WindowHandler());
    shape.add(new MenuItem("Polygon", new MenuShortcut(kControlP))).addActionListener(new WindowHandler());
    shape.add(new MenuItem("Draw Polygon", new MenuShortcut(kControlD))).addActionListener(new WindowHandler());
    about.add(new MenuItem("About", new MenuShortcut(kControlA))).addActionListener(new WindowHandler());
    ...
  }
  ...
  //Inner class to handle events
  private class WindowHandler extends WindowAdapter implements ActionListener
  {
    public void windowClosing(WindowEvent e)
    {
      System.exit(0);
    }
    public void actionPerformed(ActionEvent e)
    {
      System.out.println(e.getActionCommand());
      //check to see if the action command is equal to exit
      if(e.getActionCommand().equalsIgnoreCase("exit"))
      {
        System.exit(0);
      }
      else if(e.getActionCommand().equalsIgnoreCase("About"))
      {
        JOptionPane.showMessageDialog(null, "This small freeware program is written by Yasir Feroze Minhas.", "About", JOptionPane.PLAIN_MESSAGE);
      }
      else
      {
        JOptionPane.showMessageDialog(null, "You asked for a "+e.getActionCommand(), "A Simple Drawing Tool", JOptionPane.PLAIN_MESSAGE);
      }
    }//actionPerformed()
  }//windowHandler - Inner Class ends here
}

第 4 步：編寫一個(gè) Shapes 類

現(xiàn)在是時(shí)候?qū)懴挛覀兊?Shapes 類了。我們使用一種方法將 Shapes 類定義為抽象類draw()，然后將其擴(kuò)展為 Rectangle、Oval、Triangle 和 Polygon 的具體類。然后我們使用多態(tài)根據(jù)傳遞的上述具體類的運(yùn)行時(shí)對象繪制不同的形狀。

/**
  This is the abstract parent class for different shape classes,
  like rectangle, oval, polygon and triangle. It provides an abstract
  method draw().
*/
package graph;
import java.util.*;
import java.awt.*;
public abstract class Shapes 
{
  /**abstract method draw()
    @return void
  */
  public abstract void draw(java.util.List list, Graphics g);
}
//different implementations of Shape class
class RectangleShape extends Shapes
{
  Point sPoint = null;
  Point ePoint = null;
  public void draw(java.util.List list, Graphics g)
  {
    Iterator it = list.iterator();
    //if the list does not contain the required two points, return.
    if(list.size()<2)
    {
      return;
    }
    sPoint = (Point)it.next();
    ePoint = (Point)it.next();
    if(sPoint == null || ePoint == null)
    {
      return;
    }
    else
    {
      g.fillRect((int)sPoint.getX(), (int)sPoint.getY(), (int)(ePoint.getX()-sPoint.getX()),
      (int)(ePoint.getY()-sPoint.getY()));
    }//end of if
    list.clear();
  }//end of draw for rectangle
}//rectangle
class OvalShape extends Shapes
{
  Point sPoint = null;
  Point ePoint = null;
  public void draw(java.util.List list, Graphics g)
  {
    Iterator it = list.iterator();
    //if the list does not contain the required two points, return.
    if(list.size()<2)
    {
      return;
    }
    sPoint = (Point)it.next();
    ePoint = (Point)it.next();
    if(sPoint == null || ePoint == null)
    {
      return;
    }
    else
    {
      g.fillOval((int)sPoint.getX(), (int)sPoint.getY(), (int)(ePoint.getX()-sPoint.getX()),
      (int)(ePoint.getY()-sPoint.getY()));
    }//end of if
    list.clear();
  }//end of draw for Oval
}//OvalShape
class TriangleShape extends Shapes
{
  public void draw(java.util.List list, Graphics g)
  {
    Point point = null;
    Iterator it = list.iterator();
    //if the list does not contain the required two points, return.
    if(list.size()<3)
    {
      return;
    }
    Polygon p = new Polygon();
    for(int i = 0; i < 3; i++)
    {
      point = (Point)it.next();
      p.addPoint((int)point.getX(), (int)point.getY());
    }
    g.fillPolygon(p);
    list.clear();
  }//end of draw for Triangle
}//Triangle
class PolygonShape extends Shapes
{
  public void draw(java.util.List list, Graphics g)
  {
    Point point = null;
    Iterator it = list.iterator();
    //if the list does not contain the required two points, return.
    if(list.size()<3)
    {
      return;
    }
    Polygon p = new Polygon();
    for(;it.hasNext();)
    {
      point = (Point)it.next();
      p.addPoint((int)point.getX(), (int)point.getY());
    }
    g.fillPolygon(p);
    list.clear();
  }//end of draw for Polygon
}//Polygon

步驟 5：添加用于繪制形狀的面板并編寫適當(dāng)?shù)氖录幚沓绦?/h2>

現(xiàn)在我們向我們的簡單繪圖工具添加一個(gè)面板并重寫我們的 WindowHandler 類，以便它啟用/禁用菜單選擇并將相應(yīng)的 Shapes 對象傳遞給面板進(jìn)行繪圖。這是actionPerformedSimpleDrawingTool 和 DrawingPanel 類的更改方法。

public void actionPerformed(ActionEvent e)
    {
      //check to see if the action command is equal to exit
      if(e.getActionCommand().equalsIgnoreCase("exit"))
      {
        System.exit(0);
      }
      else if(e.getActionCommand().equalsIgnoreCase("Rectangle"))
      {
        Menu menu = getMenuBar().getMenu(1);
        for(int i = 0;i < menu.getItemCount();menu.getItem(i).setEnabled(true),i++);
        getMenuBar().getShortcutMenuItem(new MenuShortcut(kControlR)).setEnabled(false);
        panel.drawShape(rectangle);
      }
      else if(e.getActionCommand().equalsIgnoreCase("Circle"))
      {
        Menu menu = getMenuBar().getMenu(1);
        for(int i = 0;i < menu.getItemCount();menu.getItem(i).setEnabled(true),i++);
        getMenuBar().getShortcutMenuItem(new MenuShortcut(kControlC)).setEnabled(false);
        panel.drawShape(oval);
      }
      else if(e.getActionCommand().equalsIgnoreCase("Triangle"))
      {
        Menu menu = getMenuBar().getMenu(1);
        for(int i = 0;i < menu.getItemCount();menu.getItem(i).setEnabled(true),i++);
        getMenuBar().getShortcutMenuItem(new MenuShortcut(kControlT)).setEnabled(false);
        panel.drawShape(triangle);
      }
      else if(e.getActionCommand().equalsIgnoreCase("Polygon"))
      {
        Menu menu = getMenuBar().getMenu(1);
        for(int i = 0;i < menu.getItemCount();menu.getItem(i).setEnabled(true),i++);
        getMenuBar().getShortcutMenuItem(new MenuShortcut(kControlP)).setEnabled(false);
        panel.drawShape(polygon);
      }
      else if(e.getActionCommand().equalsIgnoreCase("Draw Polygon"))
      {
        Menu menu = getMenuBar().getMenu(1);
        for(int i = 0;i < menu.getItemCount();menu.getItem(i).setEnabled(true),i++);
        getMenuBar().getShortcutMenuItem(new MenuShortcut(kControlP)).setEnabled(false);
        panel.repaint();
      }
      else if(e.getActionCommand().equalsIgnoreCase("About"))
      {
        JOptionPane.showMessageDialog(null, "This small freeware program is written by Yasir Feroze Minhas.", "About", JOptionPane.PLAIN_MESSAGE);
      }
    }//actionPerformed()
class DrawingPanel extends Panel implements MouseListener
{
  private Point sPoint = null;
  private Point ePoint = null;
  private Shapes shape = null;
  private java.util.ArrayList list = new java.util.ArrayList();
  //override panel paint method to draw shapes
  public void paint(Graphics g)
  {
    g.setColor(Color.green);
    shape.draw(list, g);
  }
  public void drawShape(Shapes shape)
  {
    this.shape = shape;
  }
  //define mouse handler
  public void mouseClicked(MouseEvent e)
  {
    //if user wants to draw triangle, call repaint after 3 clicks
    if(shape instanceof TriangleShape)
    {
      list.add(e.getPoint());
      if(list.size() > 2)
      {
        repaint();
      }
    }
    else if(shape instanceof PolygonShape)
    {
      list.add(e.getPoint());
    }
  }//mouseClicked
  public void mouseEntered(MouseEvent e){}
  public void mouseExited(MouseEvent e){}
  public void mousePressed(MouseEvent e)
  {
    sPoint = e.getPoint();
  }//mousePressed
  public void mouseReleased(MouseEvent e)
  {
    ePoint = e.getPoint();
    if(ePoint.getX() < sPoint.getX())
    {
      Point temp = ePoint;
      ePoint = sPoint;
      sPoint = temp;
    }
    if(ePoint.getY() < sPoint.getY())
    {
      int temp = (int)ePoint.getY();
      ePoint.y = (int)sPoint.getY();
      sPoint.y = temp;
    }
    if(shape instanceof RectangleShape || shape instanceof OvalShape)
    {
      list.clear();
      list.add(sPoint);
      list.add(ePoint);
      repaint();
    }
  }//mouseReleased
}//DrawingPanel

現(xiàn)在我們完成了我們的 SimpleDrawingTool，并且可以使用鼠標(biāo)在其面板上繪制基本的幾何形狀。然而，這段代碼仍然存在一些問題，我們將在下一版本的 SimpleDrawingTool 中回來重新審視這段代碼，并增強(qiáng)它以包括填充顏色選擇和鼠標(biāo)移動(dòng)跟蹤線，同時(shí)繪制具有更好菜單的形狀對象選擇選項(xiàng)。

在Java學(xué)習(xí)中會(huì)運(yùn)用到很的開發(fā)工具，大家可都要熟練使用哦。