Java Graphics實現界面顯示文字並換行

 public class Main {
    
    public  static void main(String[] strings)
    {
        String poem = "破陣子·為陳同甫賦壯詞以寄之\r\n"
        + "作者：辛棄疾\r\n"
        + "\r\n"
        + "醉裡挑燈看劍，夢回吹角連營。八百裡分麾下炙，五十弦翻塞外聲，沙場秋點兵。\r\n"
        + "馬作的盧飛快，弓如霹靂弦驚。瞭卻君王天下事，贏得生前身後名。可憐白發生！";
 
        AlgoFrame frame = new AlgoFrame("Java",poem, 600, 600);
        System.out.print("行路難，行路難，多歧路，今安在？\n"
                + "醉裡挑燈看劍，夢回吹角連營");
    }
}

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
 
import javax.swing.*;
 
public class AlgoFrame extends JFrame {
    private int canvasWidth;
    private int canvasHeight;
    public AlgoFrame(String title, String poem, int canvasWidth, int canvasHeight){
 
        super(title);
 
        this.canvasHeight = canvasHeight;
        this.canvasWidth = canvasWidth;
 
 
//        AlgoCanvas canvas = new AlgoCanvas();
        AlgoCanvas canvas = new AlgoCanvas(poem);
        
        setContentPane(canvas);
        pack();
                
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }
 
    public AlgoFrame(String title){
        this(title, "", 1024, 768);
    }
 
 
    public int getCanvasWidth(){return  canvasWidth;}
    public int setCanvasHeight() {return canvasHeight;}
 
    private class AlgoCanvas extends JPanel{
        
        Font pf = new Font("Helvetica", Font.BOLD,20);
        String poem = "";
        
//        String poem = "破陣子·為陳同甫賦壯詞以寄之\r\n"
//                + "作者：辛棄疾\r\n"
//                + "\r\n"
//                + "醉裡挑燈看劍，夢回吹角連營。八百裡分麾下炙，五十弦翻塞外聲，沙場秋點兵。\r\n"
//                + "馬作的盧飛快，弓如霹靂弦驚。瞭卻君王天下事，贏得生前身後名。可憐白發生！";
        
        public AlgoCanvas (String strs) {
            this.poem = strs;
        }
    
        
        @Override
        public void paintComponent(Graphics gra) {
            
            Graphics2D graphics2d = (Graphics2D)gra;
            int strokeWidth = 5;
            graphics2d.setStroke(new BasicStroke(strokeWidth));
            
            graphics2d.setColor(Color.RED);
            Ellipse2D circle = new Ellipse2D.Double(60, 60, 300, 300);
            graphics2d.draw(circle);
            
            graphics2d.setColor(Color.BLACK);
            Rectangle2D rect = new Rectangle2D.Double(50, 50, 320, 320);
            graphics2d.draw(rect);
            
            graphics2d.setColor(Color.blue);
            Ellipse2D circle2 = new Ellipse2D.Float(80, 80, 260, 260);
//            graphics2d.draw(circle2);
            graphics2d.fill(circle2);
            
            
//            顯示辛棄疾的詞
            graphics2d.setColor(Color.black);
//            graphics2d.setFont(pf);
//            graphics2d.drawString(poem, 10, canvasHeight-100);
            
            drawStringWithFontStyleLineFeed(graphics2d,poem, 10, canvasHeight-100, pf);
            
        }
        
        @Override
        public Dimension getPreferredSize() {
//            System.out.println("running");
            return new Dimension(canvasWidth, canvasHeight);
        }
        
        
        //字符串總寬度
        private int  getStringLength(Graphics g, String str) {
            char[]  strcha=str.toCharArray();
            int strWidth = g.getFontMetrics().charsWidth(strcha, 0, str.length());
            System.out.println("字符總寬度:"+strWidth);
            return strWidth;
        }
        
        
//        //每一行字符串寬度  自定義  也就是畫佈中一行的寬度
//        int rowWidth=1110;  
//        //字符串字符的個數 
//        int strnum= str.length();
//        //每一行字符的個數
        
        private int getRowStrNum(int strnum,int rowWidth,int strWidth)
        {
            int rowstrnum=0;
            rowstrnum=(rowWidth*strnum)/strWidth;
            System.out.println("每行的字符數:"+rowstrnum);
            return rowstrnum;
        }
        
        //字符行數
        private  int  getRows(int strWidth,int rowWidth){
            int rows=0;
            if(strWidth%rowWidth>0){
                rows=strWidth/rowWidth+1;
            }else{
                rows=strWidth/rowWidth;
            }
            System.out.println("行數:"+rows);
            return rows;
        }
        
        //字符高度
        private int  getStringHeight(Graphics g) {
            int height = g.getFontMetrics().getHeight();
            System.out.println("字符高度:"+height);
            return height;
        }
        
//        註意設置font 才能計算寬度和高度
//        開始繪制
        private  void  drawStringWithFontStyleLineFeed(Graphics g, String strContent, int loc_X, int loc_Y, Font font)
        {
            g.setFont(font);
            
            //獲取字符串 字符的總寬度
            int strWidth = getStringLength(g,strContent);
            
            //每一行字符串寬度
            int rowWidth = 500;
            System.out.println("每行字符寬度:"+rowWidth);
            
            //獲取字符高度
            int strHeight=getStringHeight(g);
            
            //字符串總個數
            System.out.println("字符串總個數:"+strContent.length());
            if(strWidth>rowWidth){
                
                int rowstrnum=getRowStrNum(strContent.length(),rowWidth,strWidth);
                int  rows= getRows(strWidth,rowWidth);
                
                String temp="";
                for (int i = 0; i < rows; i++) {
                    //獲取各行的String 
                    if(i==rows-1){
                        //最後一行
                        temp=strContent.substring(i*rowstrnum,strContent.length());
                    }else{
                        temp=strContent.substring(i*rowstrnum,i*rowstrnum+rowstrnum);
                    }
                    if(i>0){
                        //第一行不需要增加字符高度，以後的每一行在換行的時候都需要增加字符高度
                        loc_Y=loc_Y+strHeight;
                    }
                    g.drawString(temp, loc_X, loc_Y);
                }
            }else{
                //直接繪制
                g.drawString(strContent, loc_X, loc_Y);
            }
            
        }
    }
 
}