在第一部分中，我们实现了5个类。在本部分中，我们接着说明如何利用UML类图来设计余下的各个类。为减少篇幅，本部分着重讲解UML类图及应用，对Java实现代码不再详细描述。
六、CGPoint类
CGPoint类说明了如何利用非抽象类扩展抽象类。CGPoint类是CGObject的子类，CGPoint类扩展了CGObject类，CGPoint类没有再它所继承的变量中增加变量，它所声明的方法只有构造函数和要求它实现的抽象方法。其类图如下：
Java实现代码为：
// CGPoint.java
public class CGPoint extends CGObject {
// Method declarations
public CGPoint(int x, int y,char ch) {
location = new Point(x,y);
drawCharacter = ch;
}
public CGPoint(int x, int y) {
this(x,y,'+');
}
public CGPoint(Point p) {
this(p.getX(),p.getY(),'+');
}
public CGPoint(Point p,char ch) {
this(p.getX(),p.getY(),ch);
}
public void display(PrintCGrid grid) {
grid.setCharAt(drawCharacter,location);
}
public void describe() {
System.out.print("CGPoint "+String.valueOf(drawCharacter)+" ");
System.out.println(location.toString());
}
}
七、CGBox类
CGBox类也扩展了CGObject类。CGBox类提供了在网格上显示矩形的附加变量。CGBox类的类图如下：
相应的代码为：
// CGBox.java
public class CGBox extends CGObject {
// Variable declarations
protected Point lr; // Lower right corner of a box
// Method declarations
public CGBox(Point ulCorner, Point lrCorner,char ch) {
location = ulCorner;
lr = lrCorner;
drawCharacter = ch;
}
public CGBox(Point ulCorner, Point lrCorner) {
this(ulCorner,lrCorner,'#');
}
public void display(PrintCGrid grid) {
int width = lr.getX() - location.getX() + 1;
int height = lr.getY() - location.getY() + 1;
Point topRow = new Point(location);
Point bottomRow = new Point(location.getX(),lr.getY());
for(int i=0; i<width; ++i) {
grid.setCharAt(drawCharacter,topRow);
grid.setCharAt(drawCharacter,bottomRow);
topRow = topRow.add(1,0);
bottomRow = bottomRow.add(1,0);
}
Point leftCol = new Point(location);
Point rightCol = new Point(lr.getX(),location.getY());
for(int i=0;i>height;++i){
grid.setCharAt(drawCharacter,leftCol);
grid.setCharAt(drawCharacter,rightCol);
leftCol = leftCol.add(0,1);
rightCol = rightCol.add(0,1);
}
}
public void describe() {
System.out.print("CGBox "+String.valueOf(drawCharacter)+" ");
System.out.println(location.toString()+" "+lr.toString());
}
}
八、CGText类
CGText类是CGObject中的第三个子类。其类图与代码分别如下：
// CGText.java
public class CGText extends CGObject {
// Variable declarations
String text;
// Method declarations
public CGText(Point p,String s) {
location = p;
drawCharacter = ' ';
text = s;
}
public void display(PrintCGrid grid) {
Point p = new Point(location);
for(int i=0;i<text.length();++i){
grid.setCharAt(text.charAt(i),p);
p = p.add(1,0);
}
}
public void describe() {
System.out.println("CGText "+location.toString()+" "+text);
}
}>
以下是CGObject类、CGPoint类、CGBox类、CGText类及Point类之间的相互关系。注意CGObject类是抽象类，其类名用斜体表示。
九、KeyboardInput类
KeyboardInput类扩展了Java API的DataInputStream类，用来提供获取用户键盘输入的一系列常用的简单方法。其类图设计为：
代码为：
import java.lang.System;
import java.io.DataInputStream;
import java.io.InputStream;
import java.io.IOException;
//KeyboardInput.java
public class KeyboardInput extends DataInputStream {
public KeyboardInput(InputStream inStream) {
super(inStream);
}
public char getChar() throws IOException {
String line = readLine();
if(line.length()==0) return ' ';
return line.charAt(0);
}
public String getText() throws IOException {
String line = readLine();
return line;
}
public int getInt() throws IOException {
String line = readLine();
Integer i = new Integer(line);
return i.intValue();
}
public Point getPoint() throws IOException {
System.out.print(" x-coordinate: ");
System.out.flush();
int x = getInt();
System.out.print(" y-coordinate: ");
System.out.flush();
int y = getInt();
return new Point(x,y);
}
}
十、CDrawApp类
主程序由CDrawApp类所构成。它包含main()方法，main()方法建立类CDraw的对象，然后调用该对象的run()方法。其中CDraw类属于内部类，当然你也可以将它单独作为一个类文件编辑、编译，其效果是一样的。
其中类与内部类之间的关系，用关联关系来表达，外部类用一个十字交叉圆圈表示，箭头指向内部类。如下图所示：
其代码实现为：
import java.lang.System;
import java.io.DataInputStream;
import java.io.IOException;
//CDrawApp.java
class CDrawApp {
public static void main(String args[]) throws IOException {
CDraw program = new CDraw();
program.run();
}
}
class CDraw {
// Variable declarations
static KeyboardInput kbd = new KeyboardInput(System.in);
BorderedPrintCGrid grid;
// Method declarations
CDraw() {
grid = new BorderedPrintCGrid();
}
void run() throws IOException {
boolean finished = false;
do {
char command = getCommand();
switch(command){
case 'P':
addPoint();
System.out.println();
break;
case 'B':
addBox();
System.out.println();
break;
case 'T':
addText();
System.out.println();
break;
case 'U':
grid.deleteLastObject();
System.out.println();
break;
case 'C':
grid.clearGrid();
System.out.println();
break;
case 'S':
grid.show();
break;
case 'X':
finished = true;
default:
System.out.println();
}
} while (!finished);
}
char getCommand() throws IOException {
System.out.println("CDrawApp P - Add a Point U - Undo Last Add");
System.out.print ("Main Menu B - Add a Box C - Clear Grid");
System.out.println(" X - Exit CDrawApp");
System.out.print (" T - Add Text S - Show Grid ");
System.out.print (" Enter command: ");
System.out.flush();
return Character.toUpperCase(kbd.getChar());
}
void addPoint() throws IOException {
System.out.println("Add Point Menu");
System.out.println(" Location:");
Point p = kbd.getPoint();
System.out.print(" Character: ");
System.out.flush();
char ch = kbd.getChar();
if(ch==' ') ch = '+';
CGPoint cgp = new CGPoint(p,ch);
cgp.addToGrid(grid);
}
void addBox() throws IOException {
System.out.println("Add Box Menu");
System.out.println(" Upper Left Corner:");
Point ul = kbd.getPoint();
System.out.println(" Lower Right Corner:");
Point lr = kbd.getPoint();
System.out.print(" Character: ");
System.out.flush();
char ch = kbd.getChar();
if(ch==' ') ch = '#';
CGBox box = new CGBox(ul,lr,ch);
box.addToGrid(grid);
}
void addText() throws IOException {
System.out.println("Add Text Menu");
System.out.println(" Location:");
Point p = kbd.getPoint();
System.out.print(" Text: ");
System.out.flush();
String text = kbd.getText();
CGText cgt = new CGText(p,text);
cgt.addToGrid(grid);
}
}
主程序CDrawApp类与相应类之间的关系为：
按照本文次序分别编译以上的10个大类，然后运行主程序CdrawApp即可。在程序运行时请注意：当选择增加点、框或者文本串后，选择Show Grid才能出现网格，并显示结果。
本文通过一个具体的程序开发过程，详细说明了如何使用UML类图来设计Java应用程序，使得程序开发可视化，文档标准化，便于相互协作与管理，是Java应用程序开发的方向。
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