sortfieldsmidlet.java

j2me的程序

import java.io.*;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.rms.*;

public class SortFieldsMIDlet extends MIDlet
implements CommandListener {

  private Command exitCommand;
  private Display display;
  private String[] names = {"黄聪明","陈小筱","黄镇樟","郑雅文"};
  private int[] chineseScore = {74,98,89,76};
  private int[] englishScore = {67,89,89,78};
  private int[] mathScore = {80,76,80,78};

  public SortFieldsMIDlet() {
    display = Display.getDisplay(this);
    exitCommand = new Command("离开", Command.EXIT, 1);
  }

  public void startApp() {
	TextBox aTextBox = new TextBox("主画面",null,256,TextField.ANY);

	RecordStore rs = null;
	byte[] nameEmail=null;
	boolean existingOrNot = false;
	boolean OK = true;

	existingOrNot = existing("aRS3");
	if(existingOrNot){
	   try{
		rs = RecordStore.openRecordStore("aRS3",false);
            }
            catch(Exception e){
		OK = false;
	   }
	   finally{
		 if(OK){
			 aTextBox.setString("aRS3已存在并且已打开");
	          }
	          else{
			aTextBox.setString("aRS3已存在但无法打开");
	          }
            }
        }
        else{
	try{
		rs = RecordStore.openRecordStore("aRS3",true);
	    }
             catch(Exception e){
		OK = false;
	    }
	    finally{
		if(OK){
	    	aTextBox.setString("aRS3虽未存在，但已创建并完成打开的操作!");
		}
		else{
	    	aTextBox.setString("aRS3虽未存在，但无法创建，打开文件失败!");
		}
	}
	}

    Student aStudent = null;

    if(OK)
       try{
		   for(int i=0;i<names.length;i++){
			  aStudent = new Student();
			  aStudent.write(names[i],
			                 chineseScore[i],
			                 englishScore[i],
			                 mathScore[i]
			                );
	    	  byte[] data = aStudent.changeToByteArray();
	    	  int recordID = aStudent.getRecordID();
	    	  if(recordID != -1){
	    	    rs.setRecord(recordID,data,0,data.length);
			  }
	    	  else{
				recordID = rs.addRecord(data,0,data.length);
			  	aStudent.setRecordID(recordID);
		  	  }
		  	  aStudent = null;
		    }
			aTextBox.setString("已完成新增记录的操作!");
		  }
	   catch(Exception e){
			aTextBox.setString("新增记录的操作失败!");
	   }

    String result="";
    aStudent = new Student();


    if(OK)
       try{
		   byte[] data;
		   int number = 0;
		   RecordComparator rc = new sortByAverage();
		   RecordEnumeration re = rs.enumerateRecords(null,rc,false);
		   while(re.hasNextElement()){
			   int recordID = re.nextRecordId();
			   data = rs.getRecord(recordID);
			   aStudent.changeFromByteArray(data);
			   result += "第" + recordID + "笔\n" +
			             "姓名:" + aStudent.getName() + "\n" +
			   		"语文:" + aStudent.getChineseScore() + "\n" +
	                                "英语:" + aStudent.getEnglishScore() + "\n" +
	                                "数学:" + aStudent.getMathScore() + "\n";
	           number++;
	       }
 	        result += "共有" + number + "笔记录:\n";
	    	aTextBox.setString(result);
		  }
	   catch(Exception e){
		   aTextBox.setString("获取记录的操作失败!"  );
		   try{
				rs.closeRecordStore();
				System.out.println("1.Closed.");
		        RecordStore.deleteRecordStore("aRS3");
				System.out.println("delete OK");
			}
			catch(Exception x){
            }
	   }
    finally{
	   try{
		   if(rs != null) rs.closeRecordStore();
		   rs.deleteRecordStore("aRS3");
	   }
	   catch(Exception e){
	   }
	}

    aTextBox.setString(result);
    aTextBox.addCommand(exitCommand);
    aTextBox.setCommandListener(this);
    display.setCurrent(aTextBox);
  }

  public void pauseApp() {
  }
  public void destroyApp(boolean unconditional) {
  }

  public boolean existing(String recordStoreName) {
    boolean existingOrNot = false;
    RecordStore rs = null;
    if(recordStoreName.length() > 32) return false;
    try{
	    rs = RecordStore.openRecordStore(recordStoreName,false);
    }
    catch(RecordStoreNotFoundException e){
	    existingOrNot = false;
    }
    catch(Exception e){
    }
    finally{
    	try{
	        rs.closeRecordStore();
	    }
	    catch(Exception e){
	    }
    }
   return existingOrNot;
  }

  public void commandAction(Command c, Displayable s) {
     destroyApp(false);
     notifyDestroyed();
  }
}

class sortByAverage implements RecordComparator{
	public int compare(byte[] rec1, byte[] rec2){
		DataInputStream student1 = new DataInputStream(new ByteArrayInputStream(rec1));
		DataInputStream student2 = new DataInputStream(new ByteArrayInputStream(rec2));
		int average1 = 0;
		int average2 = 0;
		try{
		   String dummy = student1.readUTF();
		   average1 = (student1.readInt() +
		               student1.readInt() +
		               student1.readInt())/3;

		   dummy = student2.readUTF();
		   average2 = (student2.readInt() +
		   		       student2.readInt() +
		               student2.readInt())/3;

	   }
	   catch(Exception e){
	   }

	   if(average1 == average2 ) return RecordComparator.EQUIVALENT;
	   else if(average1 < average2) return RecordComparator.FOLLOWS;
	   else return RecordComparator.PRECEDES;

	}
}