java 画矩形

请问一下如何能在java中根据给定的坐标，长宽，画出矩形，这个矩形是由*号或其他符号拼成的。如下面的格式

• *
• *
• *
• * * * * * * * * * * * *

我用先拼成字符串形式，然后调用drawString()方法，只能打印出一行，无法识别出换行。不知道该用什么方法解决？
[code="java"]
package assignment.task1;

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class Window {
private int numberOfRows;
private int numberOfColumns;
private char borderCharacter;

Frame f = new Frame("Drawing");


Window(int numberOfRows,int numberOfColumns,char borderCharacter){
    this.numberOfRows=numberOfRows;
    this.numberOfColumns=numberOfColumns;
    this.borderCharacter=borderCharacter;
}

public void addShape(Object obj) {

}

public void removeShape(){

}

public void display(){
    MyCanvas p = new MyCanvas();
    WL wl = new WL();
    String str = drawWin().toString();
    p.getWin(str);

    System.out.println(str);

    f.add(p);
    f.setSize(600,400);
    f.setVisible(true); 

    f.addWindowListener(wl);
}

public StringBuffer drawWin(){
    StringBuffer str=new StringBuffer();
    int m =numberOfRows;
    int n =numberOfColumns;

      for(int i=0;i<=m;i++){
            for(int j=0;j<=n;j++){
                    if(i==0){
                        str.append(borderCharacter+" ");
                    }else if(i>0 && i<m){
                                if(j==0 || j==n){
                                    str.append(borderCharacter+" ");
                                }else{
                                    str.append("  ");
                                }
                    }else if(i==m){
                        str.append(borderCharacter+" ");
                    }                       

            }
            str.append("\n");
        }

    return str;
}

class WL extends WindowAdapter{
    public void windowClosing(WindowEvent e){
        f.setVisible(false);
    }

}

}

class MyCanvas extends Canvas{
String win;

public void getWin(String str){
    this.win = str;
}

public void paint(Graphics g){

    String s = win;
    g.drawString(s,10,20);


}   

}
[/code]

[code="java"]
package org.zergle.test.swing;

import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Point;
import java.util.Arrays;

import javax.swing.JFrame;
import javax.swing.JPanel;

/**

• 星号组成的矩形
• @author Johnson Lee

• */
  public class StarRectangle {
  private Point location;
  private int width;
  private int height;

  public StarRectangle(Point location, int width, int height) {
  this.location = location;
  this.width = width;
  this.height = height;
  }

  /**

  • 绘制自己

  • @param g
    /
    public void draw(Graphics g) {
    char[] top = new char[width];
    char[] mid = new char[width];
    Arrays.fill(top, '');
    Arrays.fill(mid, ' ');
    mid[0] = '*';
    mid[mid.length - 1] = '*';

    Font font = g.getFont();
    // 设置字体为等宽字体
    g.setFont(new Font("Courier New", Font.PLAIN, 10));
    FontMetrics fm = g.getFontMetrics();
    int x = location.x;
    int y = location.y;
    int h = fm.getHeight();

    g.drawChars(top, 0, top.length, x, y);
    if (this.height >= 2) {
    y += h;
    for (int i = 0; i < this.height - 2; i++) {
    g.drawChars(mid, 0, mid.length, x, y);
    y += h;
    }
    g.drawChars(top, 0, top.length, x, y);
    }
    g.setFont(font);
    }

  /**

  • @param args */ public static void main(String[] args) { new Canvas(); }

}

/**

• 画布
• @author Johnson Lee

• */
  class Canvas extends JFrame {

  public Canvas() {
  this.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
  this.setContentPane(new JPanel() {

      public void paint(Graphics g) {
          new StarRectangle(new Point(130, 100), 50, 5).draw(g);
      }
  
  });
  this.setSize(600, 400);
  this.setVisible(true);
  

  }
  }
  [/code]

/** 
 * Draws the text given by the specified string, using this 
 * graphics context's current font and color. The baseline of the 
 * leftmost character is at position (<i>x</i>,&nbsp;<i>y</i>) in this 
 * graphics context's coordinate system. 
 * @param       str      the string to be drawn.
 * @param       x        the <i>x</i> coordinate.
 * @param       y        the <i>y</i> coordinate.
 * @throws NullPointerException if <code>str</code> is <code>null</code>.
 * @see         java.awt.Graphics#drawBytes
 * @see         java.awt.Graphics#drawChars
 */
public abstract void drawString(String str, int x, int y);

drawString("****", 10, 20)
drawString("* *", 10, 40)
y轴要变的