Bag Implementations That Use Arrays - Data Structures and Abstractions with Java - page 50

Revise the definition of the method add to always accommodate a new entry. The method
will never return false.

●

Revise the definition of the method isFull to always return false. A bag will never become full.

●

Revising the method add is the only substantial task in this list. The rest of the class will remain
unchanged.

2.37

The method add . Here is the original definition of the method add , as it appears in Segment 2.10:

/** Adds a new entry to this bag.
@param newEntry the object to be added as a new entry
@return true if the addition is successful, or false if not */
public boolean add(T newEntry)
{

boolean result = true ;
if (isFull())
{

result = false ;

}
else
{ // assertion: result is true here
bag[numberOfEntries] = newEntry;
numberOfEntries++;
} // end if
return result;
} // end add
Since the bag will never be full, the method isFull will always return false. Thus, we can no lon-
ger call isFull to see whether the array bag is full. Instead, we can define a private method to both
make this check and resize the array bag , if necessary. Let's name the method ensureCapacity and
specify it as follows:

// Doubles the size of the array bag if it is full.
private void ensureCapacity()
Assuming that we have defined this private method, we can revise the method add as follows:

public boolean add(T newEntry)
{

ensureCapacity();
bag[numberOfEntries] = newEntry;
numberOfEntries++;
return true ;
} // end add

2.38

The private method ensureCapacity . The array bag is full when numberOfEntries equals the
array's length, bag.length . When that is the case, we will resize bag using the technique described
earlier in Segment 2.34. Thus, the definition of ensureCapacity is straightforward:

// Doubles the size of the array bag if it is full.
private void ensureCapacity()
{

if (numberOfEntries == bag.length)
bag = Arrays.copyOf(bag, 2 * bag.length);
} // end ensureCapacity

2.39

The class ResizableArrayBag . Our new class is available online from the topic's website. You
should examine its details.