• Download the attached files into DrJava: BagInterface.java, ArrayBag.java.
• Write a Java program to put the first six capital letters of the alphabet {"A", "B", "C", "D", "E", "F"} into a BagInterface b0 as Strings. Then print the contents of the bag.
• Attach the lab Lab113.java. CopyAndPaste the compiler output window.

BagInterface.java

/** An interface that describes the operations of a bag of objects. @author Frank M. Carrano @author Timothy M. Henry @version 5.0 */ public interface BagInterface { /** Gets the current number of entries in this bag. @return The integer number of entries currently in the bag. */ public int getCurrentSize(); /** Sees whether this bag is empty. @return True if the bag is empty, or false if not. */ public boolean isEmpty(); /** 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); /** Removes one unspecified entry from this bag, if possible. @return Either the removed entry, if the removal. was successful, or null. */ public T remove(); /** Removes one occurrence of a given entry from this bag, if possible. @param anEntry The entry to be removed. @return True if the removal was successful, or false if not. */ public boolean remove(T anEntry); /** Removes all entries from this bag. */ public void clear(); /** Counts the number of times a given entry appears in this bag. @param anEntry The entry to be counted. @return The number of times anEntry appears in the bag. */ public int getFrequencyOf(T anEntry); /** Tests whether this bag contains a given entry. @param anEntry The entry to find. @return True if the bag contains anEntry, or false if not. */ public boolean contains(T anEntry); /** Retrieves all entries that are in this bag. @return A newly allocated array of all the entries in the bag. Note: If the bag is empty, the returned array is empty. */ public T[] toArray(); } // end BagInterface

ArrayBag.java

/** A class of bags whose entries are stored in a fixed-size array. @author Frank M. Carrano, Timothy M. Henry @version 5.0 */ public final class ArrayBag implements BagInterface { private final T[] bag; private int numberOfEntries; private boolean integrityOK = false; private static final int DEFAULT_CAPACITY = 25; private static final int MAX_CAPACITY = 10000; /** Creates an empty bag whose initial capacity is 25. */ public ArrayBag() { this(DEFAULT_CAPACITY); } // end default constructor /** Creates an empty bag having a given capacity. @param desiredCapacity The integer capacity desired. */ public ArrayBag(int desiredCapacity) { if (desiredCapacity <= MAX_CAPACITY) { // The cast is safe because the new array contains null entries @SuppressWarnings("unchecked") T[] tempBag = (T[])new Object[desiredCapacity]; // Unchecked cast bag = tempBag; numberOfEntries = 0; integrityOK = true; // Test that contents are nulls - OK // for (int index = 0; index < desiredCapacity; index++) // System.out.print(bag[index] + " "); // System.out.println(); } else throw new IllegalStateException("Attempt to create a bag " + "whose capacity exceeds " + "allowed maximum."); } // end constructor /** 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) { checkIntegrity(); boolean result = true; if (isArrayFull()) { result = false; } else { // Assertion: result is true here bag[numberOfEntries] = newEntry; numberOfEntries++; } // end if return result; } // end add /** Retrieves all entries that are in this bag. @return A newly allocated array of all the entries in this bag. */ // public  T[] toArray() //OK public T[] toArray() //OK { checkIntegrity(); // The cast is safe because the new array contains null entries. @SuppressWarnings("unchecked") T[] result = (T[])new Object[numberOfEntries]; // Unchecked cast for (int index = 0; index < numberOfEntries; 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 empty. @return True if this bag is empty, or false if not. */ public boolean isEmpty() { return numberOfEntries == 0; } // end isEmpty /** Gets the current number of entries in this bag. @return The integer number of entries currently in this bag. */ public int getCurrentSize() { return numberOfEntries; } // end getCurrentSize /** Counts the number of times a given entry appears in this bag. @param anEntry The entry to be counted. @return The number of times anEntry appears in this ba. */ public int getFrequencyOf(T anEntry) { checkIntegrity(); int counter = 0; for (int index = 0; index < numberOfEntries; index++) { if (anEntry.equals(bag[index])) { counter++; } // end if } // end for return counter; } // end getFrequencyOf /** Tests whether this bag contains a given entry. @param anEntry The entry to locate. @return True if this bag contains anEntry, or false otherwise. */ public boolean contains(T anEntry) { checkIntegrity(); return getIndexOf(anEntry) > -1; // or >= 0 } // end contains /** Removes all entries from this bag. */ public void clear() { while (!isEmpty()) remove(); } // end clear /** Removes one unspecified entry from this bag, if possible. @return Either the removed entry, if the removal was successful, or null. */ public T remove() { checkIntegrity(); T result = removeEntry(numberOfEntries - 1); return result; } // end remove /** Removes one occurrence of a given entry from this bag. @param anEntry The entry to be removed. @return True if the removal was successful, or false if not. */ public boolean remove(T anEntry) { checkIntegrity(); int index = getIndexOf(anEntry); T result = removeEntry(index); return anEntry.equals(result); } // end remove // Returns true if the array bag is full, or false if not. private boolean isArrayFull() { return numberOfEntries >= bag.length; } // end isArrayFull // Locates a given entry within the array bag. // Returns the index of the entry, if located, // or -1 otherwise. // Precondition: checkInitialization has been called. private int getIndexOf(T anEntry) { int where = -1; boolean found = false; int index = 0; while (!found && (index < numberOfEntries)) { if (anEntry.equals(bag[index])) { found = true; where = index; } // end if index++; } // end while // Assertion: If where > -1, anEntry is in the array bag, and it // equals bag[where]; otherwise, anEntry is not in the array. return where; } // end getIndexOf // Removes and returns the entry at a given index within the array. // If no such entry exists, returns null. // Precondition: 0 <= givenIndex < numberOfEntries. // Precondition: checkInitialization has been called. private T removeEntry(int givenIndex) { T result = null; if (!isEmpty() && (givenIndex >= 0)) { result = bag[givenIndex]; // Entry to remove int lastIndex = numberOfEntries - 1; bag[givenIndex] = bag[lastIndex]; // Replace entry to remove with last entry bag[lastIndex] = null; // Remove reference to last entry numberOfEntries--; } // end if return result; } // end removeEntry // Throws an exception if this object is not initialized. private void checkIntegrity() { if (!integrityOK) throw new SecurityException("ArrayBag object is corrupt."); } // end checkIntegrity } // end ArrayBag