長い文字列を表示する時には

 int strLen = 0; //文字列の長さ
 int sizeFrameWidth = 100; //表示するフレームの幅
 int strDispLen = 0; //表示する文字列の長さ
 String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstu..."
 String dispStr = ""; //表示する文字列
 ArrayList aryList = new ArrayList(); //表示する文字列格納
 int intStart = 0;
 int intEnd   = 0; 

 strLen = strFontM.stringWidth(str);
 if(strLen > sizeFrameWidth) { 
   //文字列の長さがフレーム幅より大きい場合
   while (true) {
     dispStr = String.valueOf(strMsg.substring(intStart, intEnd));
     strDispLen = strFontM.stringWidth(dispStr);
     if(strDispLen > sizeFrameWidth) {
       aryList.add(dispStr);
       if(intEnd >= str.length()) { break; }
       intStart = intEnd;
     }
     intCntEnd++;
     if(intEnd > str.length()) { aryList.add(dispStr); break; }
   }
 } else {
   //文字列の長さがメインフレームより小さい場合
   aryList.add(str);
 }

import java.awt.Component;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.font.FontRenderContext;
import java.awt.font.LineBreakMeasurer;
import java.awt.font.TextAttribute;
import java.awt.font.TextLayout;
import java.text.AttributedCharacterIterator;
import java.text.AttributedString;
import java.util.Hashtable;
import java.util.StringTokenizer;

public class LineBreakSample extends Component {

    private Hashtable map = new Hashtable();
    private String text = 
        "東海の小島の磯の白砂にわれ泣きぬれて蟹とたはむる\n" +
        "日本語の、禁則について、試すため、点と、丸を、多く、書いてみます。これで、どうだろう。\n" +
        "  Once upon a midnight dreary, while I pondered, weak and weary, " +
        "Over many a quaint and curious volume of forgotten lore, " +
        "While I nodded, nearly napping, suddenly there came a tapping, " +
        "As of some one gently rapping, rapping at my chamber door. " +
        "\"Tis some visiter,\" I muttered, \"tapping at my chamber door -- " +
        "Only this, and nothing more.\n" + 
        "アルファベットとhiragana wo混ぜてkaitemimasita.どうなることやら";

    public LineBreakSample() {
        map.put(TextAttribute.SIZE, new Float(18.0));
    }

    public void paint(Graphics g) {
        Graphics2D g2d = (Graphics2D)g;

        float formatWidth = (float)getSize().width;
        float drawPosY = 0;
        
        StringTokenizer tok = new StringTokenizer(text, "\n");
        while (tok.hasMoreTokens()) {
            AttributedString attrStr = new AttributedString(tok.nextToken(), map);
            AttributedCharacterIterator line = attrStr.getIterator();

            int start = line.getBeginIndex();
            int end = line.getEndIndex();
            
            LineBreakMeasurer lineMeasurer = new LineBreakMeasurer(line,
                                           new FontRenderContext(null, false, false));
            lineMeasurer.setPosition(start);
            
            while (lineMeasurer.getPosition() < end) {
                
                TextLayout layout = lineMeasurer.nextLayout(formatWidth);
                drawPosY += layout.getAscent();
                
                float drawPosX;
                if (layout.isLeftToRight()) {
                    drawPosX = 0;
                } else {
                    drawPosX = formatWidth - layout.getAdvance();
                }
                
                layout.draw(g2d, drawPosX, drawPosY);
                
                drawPosY += layout.getDescent() + layout.getLeading();
            }
        }
    }

    public static void main(String[] args) {
        Frame frame = new Frame("HitTestSample");
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent event) {
                System.exit(0);
            }
        });
        
        LineBreakSample sample = new LineBreakSample();
        frame.add(sample);
        frame.setBounds(100, 100, 400, 500);
        frame.setVisible(true);
    }
}