FormattingMapElements.java

/*
 * Copyright (C) 2013 Omry Yadan <omry@yadan.net>
 * All rights reserved.
 *
 * See https://github.com/omry/banana/blob/master/BSD-LICENSE for licensing information
 */
package net.yadan.banana.map;

import net.yadan.banana.DebugLevel;
import net.yadan.banana.Formatter;
import net.yadan.banana.ICollection;
import net.yadan.banana.memory.Buffer;
import net.yadan.banana.memory.IBuffer;
import net.yadan.banana.memory.IPrimitiveAccess;

/**
 * Created by : omry Date: 6/29/13
 */
public class FormattingMapElements {

  /**
   * This usage example demonstrates using a map where the value is a variable
   * length structure. In addition, it demonstrates how to use a Formatter to
   * make debugging the map easier. All Banana data structures that implements
   * {@link ICollection} supports formatting using a Formatter, so you can reuse
   * your formatters.
   * 
   * Lets say we want the following C like struct as the value of our map. Note
   * that this is variable length struct.
   * 
   * <pre>
   * struct person {
   *  int age
   *  struct name {
   *    int size
   *    char chars[]
   *  }
   * }
   * 
   *      
   * 
   * Since banana storage is always ints, a record for 13 year old Romeo would look like
   * 
   * ┌──0──╦──1──┬──2──┬──3──┬──4──┐
   * │     ║       NAME  STRING    │
   * │ AGE ╬─────╦─────────────────┤
   * │     ║SIZE ║      CHARS      │
   * ├─────╬─────╬─────┬─────┬─────┤
   * │ 13  ║  5  ║ R|o │ m|e │ o|  │
   * └─────╩─────╩─────┴─────┴─────┘
   * 
   * Note that each int contains two chars (Java chars are 16 bit values).
   * </pre>
   */

  // Offset constants
  final static int AGE_OFFSET = 0;
  final static int NAME_SIZE_OFFSET = 1;
  final static int NAME_CHARS_OFFSET = 2;

  public static void main(String[] args) {

    // initial number of blocks in the block allocator
    int maxBlocks = 100;
    // minimal size of data we will want to put into the map (in ints)
    int blockSize = 5;
    // how full should the map be before incresing size and rehashing?
    double loadFactor = 0.75;
    // if we run out of blocks in the underlying block allocator, grow it by
    // what factor?
    double growthFactor = 2.0;
    IHashMap map = new HashMap(maxBlocks, blockSize, growthFactor, loadFactor);

    // activate map debug level
    map.setDebug(DebugLevel.DEBUG_CONTENT);

    // you can use a formatter to make the map easier to debug by using your own
    // logic to convert records to strings
    map.setFormatter(new PersonFormatter());

    long key = 1000;
    char name1[] = "Romeo".toCharArray();

    IBuffer romeo = new Buffer(10);
    romeo.setInt(AGE_OFFSET, 13);
    romeo.setInt(NAME_SIZE_OFFSET, name1.length);
    romeo.setChars(NAME_CHARS_OFFSET, name1, 0, name1.length);
    map.createRecord(key, romeo);

    long key2 = 1002;
    char name2[] = "Juliet".toCharArray();
    // this will be enough to hold the data
    int size = NAME_CHARS_OFFSET + name2.length / 2 + 1;
    // create empty record for size ints and get handle back
    int r = map.createRecord(key2, size);
    map.setInt(r, AGE_OFFSET, 13);
    map.setInt(r, NAME_SIZE_OFFSET, name2.length);
    map.setChars(r, NAME_CHARS_OFFSET, name2, 0, name2.length);

    System.out.println(map);
    /**
     * Outputs :
     * 
     * <pre>
     * Map : net.yadan.banana.map.HashMap 2 / 100
     * 1000=Romeo, age 13 (underage!)
     * 1002=Juliet, age 13 (underage!)
     * </pre>
     */
  }

  private static final class PersonFormatter implements Formatter {
    @Override
    public String format(IPrimitiveAccess parent, int pointer) {
      int age = parent.getInt(pointer, AGE_OFFSET);
      int num = parent.getInt(pointer, NAME_SIZE_OFFSET);
      char chars[] = new char[num];
      parent.getChars(pointer, NAME_CHARS_OFFSET, chars, 0, num);
      return String.format("%s, age %d%s", new String(chars), age, age < 18 ? " (underage!)" : "");
    }
  }
}