Computer Science 15-100 (Sections T & U), Spring 2008
Class Notes:  Writing Custom ArrayLists (Day 2)

Logistics

1. Schedule
   1. quiz9 Tuesday (15-April)
   2. Due tomorrow:  hw10a and hw10b
2. Reading:
   1. Ch 7.3:  Arrays of Objects

Topic Outline:

1. The Object class
    
2. Arrays of Objects
    
3. Comparable and Comparator interfaces
    
4. We deferred these topics for next lecture:
    
   1. Briefly:  MouseListener and KeyListener interfaces and MouseAdapter and KeyAdapter classes
       
   2. Iterator, ListIterator, and Iterable
       
   3. Custom ArrayList (cont)
       

Code from class:

  import java.util.*;
  @SuppressWarnings("unchecked")
  public class ComparableAndComparatorExample {
    public static void main(String[] args) throws Exception {
      MutableInteger[] a  = new MutableInteger[5];
      for (int i=0; i<a.length; i++)  a[i] = new MutableInteger(3-17*i % 7);
      System.out.println(Arrays.toString(a));
      Arrays.sort(a);
      System.out.println(Arrays.toString(a));
      Integer[] b = { -3, -2, 0, 1, 3};
      /*
      AbsValComparator comp = new AbsValComparator();
      Arrays.sort(b,comp); // sort with an UNNATURAL ordering (by absval!)
      System.out.println(Arrays.toString(b));
      AbsValComparatorForMutableInteger comp2 = new AbsValComparatorForMutableInteger();
      Arrays.sort(a,comp2); // sort with an UNNATURAL ordering (by absval!)
      System.out.println(Arrays.toString(a));
      */
      
      UberAbsValComparator comp = new UberAbsValComparator();
      Arrays.sort(b,comp); // sort with an UNNATURAL ordering (by absval!)
      System.out.println(Arrays.toString(b));
      Arrays.sort(a,comp); // sort with an UNNATURAL ordering (by absval!)
      System.out.println(Arrays.toString(a));
      
      int[] c = { 5, 3, 1, -2, -4 };
      Arrays.sort(c,comp); // sort with an UNNATURAL ordering (by absval!)
      System.out.println(Arrays.toString(c));  
    }
    
    
    public static void main1(String[] args) throws Exception {
    }
  }

  class UberAbsValComparator implements Comparator {
    public int compare(Object o1, Object o2) {
      if (o1 instanceof Integer) {
        Integer i1 = (Integer)o1;
        Integer i2 = (Integer)o2;
        return (Math.abs(i1) - Math.abs(i2));
      }
      else if (o1 instanceof MutableInteger) {
        MutableInteger i1 = (MutableInteger)o1;
        MutableInteger i2 = (MutableInteger)o2;
        return (Math.abs(i1.getValue()) - Math.abs(i2.getValue()));
      }
      else
        throw new RuntimeException("Unknown type: " + o1.getClass());
    }
  }

  class AbsValComparator implements Comparator {
    public int compare(Object o1, Object o2) {
      Integer i1 = (Integer)o1;
      Integer i2 = (Integer)o2;
      return (Math.abs(i1) - Math.abs(i2));
    }
  }

  class AbsValComparatorForMutableInteger implements Comparator {
    public int compare(Object o1, Object o2) {
      MutableInteger i1 = (MutableInteger)o1;
      MutableInteger i2 = (MutableInteger)o2;
      return (Math.abs(i1.getValue()) - Math.abs(i2.getValue()));
    }
  }
  class MutableInteger extends Object implements Comparable {
    private int value;
    public MutableInteger() {
      setValue(0);
    }
    public MutableInteger(int value) {
      setValue(value);
    }
    
    public int compareTo(Object obj) {
      MutableInteger that = (MutableInteger) obj;
      // return a negative # if (this < that)
      // return zero         if (this == that)
      // return a positive # if (this > that)
      return (this.value - that.value);
    }
    
    public String toString() {
      return "mi(" + this.value + ")";
    }
    public int inc() { return ++this.value; }
    public int getValue() { return this.value; }
    public void setValue(int value) { this.value = value; }
  }

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