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Java Masterclass for Software Developers

The Class BagOfStrings So Far

Learn how the BagOfStrings class is constructed using array-based data structures for efficient collection management. Understand the use of constructors, methods like isFull, and how to test the class with sample data. Explore the role of static methods in manipulating array contents and how objects passed as arguments can be modified within methods.

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The class and a client

The following program shows the definition of the class BagOfStrings at this point in its development. It contains only the data fields, constructors, and core methods that we have seen earlier. Before we continue the implementation of this class, we will test the class using the method main in the class BagDemo1, which is also in the code given below. Click the RUN button.

Java
/**
   A class that partially implements a bag of strings by using an array.
   @author Frank M. Carrano
*/
public class BagOfStrings
{
   private static final int DEFAULT_CAPACITY = 25; 
   private String[] bag;
   private int numberOfStrings;
   /** Creates an empty bag whose capacity is 25. */
   public BagOfStrings() 
   {
      this(DEFAULT_CAPACITY);
   } // End default constructor
   /** Creates an empty bag having a given capacity.
	    @param capacity  The integer capacity desired. */
   public BagOfStrings(int capacity) 
   {
      bag = new String[capacity];
      numberOfStrings = 0;
   } // End constructor
   /** Adds a new string to this bag.
       @param newString  The string to be added.
       @return true if the addition is successful, or false if not. */
   public boolean add(String newString) 
   {
      boolean result = true;
      if (isFull())
      {
         result = false;
      }
      else
      {  // Assertion: result is true here
         bag[numberOfStrings] = newString;
         numberOfStrings++;
      } // End if
		
      return result;
   } // End add
   
   /** Retrieves all strings that are in this bag.
       @return a newly allocated array of all the strings in this bag. */
   public String[] toArray()
   {
	  String[] result = new String[numberOfStrings];
	  for (int index = 0; index < numberOfStrings; index++) 
	  {
	     result[index] = bag[index];
	  } // End for
			
	  return result;
	  // Note: The body of this method could consist of one return statement,
	  // if you call Arrays.copyOf
   } // End toArray
   /** Sees whether this bag is full.
       @return true if this bag is full, or false if not */
   public boolean isFull() 
   {
      return numberOfStrings == bag.length;
   } // End isFull
} // End BagOfStrings

After running the previous program, you should get the following output:

Adding to an empty bag: A, A, B, A, C, A
The bag contains A A B A C A 
This bag is not full.

Adding to an empty bag: A, B, A, C, B, C, D
The bag contains A B A
...