ArrayStore.java

public abstract class ArrayStore implements STORE {
   Object[] array = new Object[10];
   int length = 0;
   public boolean isEmpty() {
      return length == 0;
   }
   protected void growTo(int newsize) {
   // Assume newsize > length 
      if(newsize > array.length) {
         int growsize = Math.max(array.length*2,1);
         while (newsize > growsize) {growsize = 2*growsize;};
         Object[] newArray = new Object[growsize];
         for (int i = 0; i < length; i++) {
            newArray[i] = array[i];
         };
         array = newArray;
      };
   }
   protected void shrinkTo(int newsize) {
   // Assume newsize <= length
      if(newsize <= array.length/2) {
         int shrinksize = array.length/2;
         while (newsize <= shrinksize/2 & shrinksize >= 2) {
            shrinksize = shrinksize/2;
         };
         Object[] newArray = new Object[shrinksize];
         for (int i = 0; i < length; i++) {
            newArray[i] = array[i];
         };
         array = newArray;
      };
   }
   public void add(Object o) {
      int ol = length;
      growTo(length+1);
      length++;
      array[ol] = o;
   }
   public void addAll(Object[] a) {
      for(int i = 0; i < a.length; i++) {
         add(a[i]);
      }
   }
   public Object remove() {
      if (isEmpty()) {length = 0; return null;};
      Object o = array[--length];
      shrinkTo(length);
      return o;
   }
   public int size() {
      return length;
   }
   public void execute(FUNCTION f) {
      if (isEmpty()) return;
      for (int i = 0; i < length; i++) {
         f.value(array[i]);
      };
   }
   public STORE map(FUNCTION f) {
      MapFunction mf = null;
      try {mf = new MapFunction((STORE)this.getClass().newInstance(),f);}
      catch (Exception e) {throw new InternalError(e.getMessage());}
      execute(mf);
      return mf.store();
   }
}

class MapFunction implements FUNCTION {
   STORE store;
   FUNCTION f;
   MapFunction(STORE s, FUNCTION f) {
      store = s;
      this.f = f;
   };
   public Object value(Object o) {
      store.add(f.value(o));
      return null;
   }
   STORE store() {
      return store;
   }
}