Java tutorial
/*-------------------------------------------------- * IntSort.java * * Sort records that contain multiple Java * data types. Sort using integer type. * * Uses: Streams, Enumeration, RecordComparator * * No GUI interface, all output is to the console * Example from the book: Core J2ME Technology * Copyright John W. Muchow http://www.CoreJ2ME.com * You may use/modify for any non-commercial purpose *-------------------------------------------------*/ import java.io.*; import javax.microedition.midlet.*; import javax.microedition.rms.*; public class IntSort extends MIDlet { private RecordStore rs = null; // Record store static final String REC_STORE = "db_4"; // Name of record store public IntSort() { openRecStore(); // Create the record store writeTestData(); // Write a series of records readStream(); // Read back the records closeRecStore(); // Close record store deleteRecStore(); // Remove the record store } public void destroyApp(boolean unconditional) { } public void startApp() { // There is no user interface, go ahead and shutdown destroyApp(false); notifyDestroyed(); } public void pauseApp() { } public void openRecStore() { try { // The second parameter indicates that the record store // should be created if it does not exist rs = RecordStore.openRecordStore(REC_STORE, true); } catch (Exception e) { // We should pay attention to the actual error thrown db(e.toString()); } } public void closeRecStore() { try { rs.closeRecordStore(); } catch (Exception e) { db(e.toString()); } } public void deleteRecStore() { if (RecordStore.listRecordStores() != null) { try { RecordStore.deleteRecordStore(REC_STORE); } catch (Exception e) { db(e.toString()); } } } /*-------------------------------------------------- * Create three arrays to write to record store *-------------------------------------------------*/ public void writeTestData() { String[] pets = { "duke", "tiger", "spike", "beauregard" }; boolean[] dog = { true, false, true, true }; int[] rank = { 3, 0, 1, 2 }; writeStream(pets, dog, rank); } /*-------------------------------------------------- * Write to record store using streams. *-------------------------------------------------*/ public void writeStream(String[] sData, boolean[] bData, int[] iData) { try { // Write data into an internal byte array ByteArrayOutputStream strmBytes = new ByteArrayOutputStream(); // Write Java data types into the above byte array DataOutputStream strmDataType = new DataOutputStream(strmBytes); byte[] record; for (int i = 0; i < sData.length; i++) { // Write Java data types strmDataType.writeUTF(sData[i]); strmDataType.writeBoolean(bData[i]); strmDataType.writeInt(iData[i]); // Clear any buffered data strmDataType.flush(); // Get stream data into byte array and write record record = strmBytes.toByteArray(); rs.addRecord(record, 0, record.length); // Toss any data in the internal array so writes // starts at beginning (of the internal array) strmBytes.reset(); } strmBytes.close(); strmDataType.close(); } catch (Exception e) { db(e.toString()); } } /*-------------------------------------------------- * Read from the record store using streams *-------------------------------------------------*/ public void readStream() { try { // Careful: Make sure this is big enough! // Better yet, test and reallocate if necessary byte[] recData = new byte[50]; // Read from the specified byte array ByteArrayInputStream strmBytes = new ByteArrayInputStream(recData); // Read Java data types from the above byte array DataInputStream strmDataType = new DataInputStream(strmBytes); if (rs.getNumRecords() > 0) { ComparatorInt comp = new ComparatorInt(); int i = 1; RecordEnumeration re = rs.enumerateRecords(null, comp, false); while (re.hasNextElement()) { // Get data into the byte array rs.getRecord(re.nextRecordId(), recData, 0); // Read back the data types System.out.println("Record #" + i++); System.out.println("Name: " + strmDataType.readUTF()); System.out.println("Dog: " + strmDataType.readBoolean()); System.out.println("Rank: " + strmDataType.readInt()); System.out.println("--------------------"); // Reset so read starts at beginning of array strmBytes.reset(); } comp.compareIntClose(); // Free enumerator re.destroy(); } strmBytes.close(); strmDataType.close(); } catch (Exception e) { db(e.toString()); } } /*-------------------------------------------------- * Simple message to console for debug/errors * When used with Exceptions we should handle the * error in a more appropriate manner. *-------------------------------------------------*/ private void db(String str) { System.err.println("Msg: " + str); } } /*-------------------------------------------------- * Compares two integers to determine sort order * Each record passed in contains multiple Java data * types - use only the integer data for sorting *-------------------------------------------------*/ class ComparatorInt implements RecordComparator { private byte[] recData = new byte[10]; // Read from a specified byte array private ByteArrayInputStream strmBytes = null; // Read Java data types from the above byte array private DataInputStream strmDataType = null; public void compareIntClose() { try { if (strmBytes != null) strmBytes.close(); if (strmDataType != null) strmDataType.close(); } catch (Exception e) { } } public int compare(byte[] rec1, byte[] rec2) { int x1, x2; try { // If either record is larger than our buffer, reallocate int maxsize = Math.max(rec1.length, rec2.length); if (maxsize > recData.length) recData = new byte[maxsize]; // Read record #1 // We want the integer from the record, which is // the last "field" thus we must read the String // and boolean to get to the integer strmBytes = new ByteArrayInputStream(rec1); strmDataType = new DataInputStream(strmBytes); strmDataType.readUTF(); strmDataType.readBoolean(); x1 = strmDataType.readInt(); // Here's our data // Read record #2 strmBytes = new ByteArrayInputStream(rec2); strmDataType = new DataInputStream(strmBytes); strmDataType.readUTF(); strmDataType.readBoolean(); x2 = strmDataType.readInt(); // Here's our data // Compare record #1 and #2 if (x1 == x2) return RecordComparator.EQUIVALENT; else if (x1 < x2) return RecordComparator.PRECEDES; else return RecordComparator.FOLLOWS; } catch (Exception e) { return RecordComparator.EQUIVALENT; } } }