This lab exercise will have you finish implementing a partially implemented IntArrayBag class which

uses a dynamically sized array as its underlying data structure. You will also write a test case for the add

method and use invariants to test and nd bugs in the add and remove methods.

1 Implement the IntArrayBag Class

1). Implement the ensureCapacity method for the IntArrayBag class. A stub for this method exists at

the bottom of the provided file.

2). Within TestIntArrayBag.java , we have already provided a test case for the ensureCapacity method.

Ensure your implementation passes this test case.

2 Find the Error with JUnit

1). Within TestIntArrayBag.java , you need to add assertions to testAdd until you have a failed test

that uncovers the error in the method.

Note 1: Do NOT correct the bug in the IntArrayBag.java though you must be able to explain what

is wrong.

Note 2: JUnit Asserts

assertTrue( condition ) , when you expect the condition to return true

assertFalse( condition ) , when you expect the condition to return false

assertEquals( result , expression) , when you expect the expression to evalute to the result.

Since the integer array data is a private field, you cannot access them directly in the assertions.

We provide the countOccurrences(Integer) method in IntArrayBag . It returns the number of

occurrences of the argument, refer to testEnsureCapacity for how to use it in assertions.

3 Find the Error with Invariant

1). Within IntArrayBag.java , you need to add the 2nd invariant checker to wellFormed . This will also

help point out bugs in your program.

2. After writing the 2nd invariant, run assertions by right-click on the project, and click Run Configurations .

This will open the Run Dialog. Displayed in Figure 1 on the following page.

3. Click the Arguments tab, and in the VM Arguments box, enter

-ea

Similar to the Figure 2 on the following page.

4. Click Run

Note: Do not correct the bug in IntArrayBag.java though you must be able to explain what is

wrong.

IntArrayBag.java

import java.util.ArrayList; import java.util.List;

public class IntArrayBag implements Cloneable { private Integer[] data; private int manyItems;

public IntArrayBag() { final int INITIAL_CAPACITY = 10; manyItems = 0; data = new Integer[INITIAL_CAPACITY]; }

public IntArrayBag(int initialCapacity) { if (initialCapacity < 0) { throw new IllegalArgumentException("initialCapacity is negative: " + initialCapacity); } manyItems = 0; data = new Integer[initialCapacity]; }

public void add(Integer element) { if (manyItems == data.length) { ensureCapacity(manyItems * 2 + 1); } data[manyItems] = manyItems + 1; manyItems++; }

private boolean _report(String message) { System.out.println(message); return false; }

private boolean wellFormed() { // Make assertions about the invariant, returning false // if the invariant false. Taken from pg 123 (3rd ed.)

// #1. manyItems should never be greater than data.length if (manyItems > data.length) return _report("manyItems is greater than data.length");

// #2. When the bag isn't empty, then items data[0] to data[manyItems-1] // should contain data (or not be null) // TODO Implement the 2nd Invariant

// All invariant assertions passed so return true return true; }

public boolean remove(Integer target) { assert wellFormed() : "Failed at the start of remove";

int index = 0; while ((index < manyItems) && (target != data[index])) { index++; }

if (index == manyItems) { return false; } else { data[index] = null; --manyItems; assert wellFormed() : "Failed at the end of remove"; return true; } }

public int size() { return manyItems; }

public int getCapacity() { return data.length; }

public int countOccurrences(int target) { int answer = 0; int index = 0;

for (index = 0; index < manyItems; index++) { if (target == data[index]) { answer++; } } return answer; }

public void ensureCapacity(int minimumCapacity) { Integer[] biggerArray; if (data.length < minimumCapacity) { biggerArray = new Integer[minimumCapacity]; System.arraycopy(data, 0, biggerArray, 0, manyItems); data = biggerArray; } // TODO implement this method // Do nothing if the current capacity is at least minimumCapacity // Otherwise make a bigger array of size minimumCapacity then copy elements over } }

TestIntArrayBag.java

import java.util.ArrayList; import java.util.List;

import junit.framework.TestCase;

public class TestIntArrayBag extends TestCase {

@Override public void setUp() { try { assert 1/(5^5) == 42 : "OK"; System.err.println("Assertions must be enabled to use this test suite."); System.err.println("In Eclipse: add -ea in the VM Arguments box under Run>Run Configurations>Arguments"); assertFalse("Assertions must be -ea enabled in the Run Configuration>Arguments>VM Arguments",true); } catch (ArithmeticException ex) { return; } } /* * This has been provided for you to test your implementation of the * ensureCapacity. */ public void testEnsureCapacity() { IntArrayBag bag = new IntArrayBag(); bag.add(1); bag.add(2); bag.add(3);

// checking below current capacity bag.ensureCapacity(3); assertFalse(bag.getCapacity() == 3); assertTrue(bag.size() == 3); assertEquals(1, bag.countOccurrences(1)); assertEquals(1, bag.countOccurrences(2)); assertEquals(1, bag.countOccurrences(3)); assertEquals(0, bag.countOccurrences(4));

// checking above current capacity bag.ensureCapacity(20); assertTrue(bag.getCapacity() == 20); assertTrue(bag.size() == 3); assertEquals(1, bag.countOccurrences(1)); assertEquals(1, bag.countOccurrences(2)); assertEquals(1, bag.countOccurrences(3)); assertEquals(0, bag.countOccurrences(4)); }

public void testRemove() { IntArrayBag bag = new IntArrayBag(); bag.add(1); bag.add(2); bag.add(3); assertEquals(3, bag.size()); bag.remove(1); assertEquals(2, bag.size()); }

/* * TODO For the below test case, you are to insert asserts until you have it * fails and you are able to find the bug. * * Some possible asserts you can use are: assertTrue( condition ) * assertFalse( condition ) assertEquals( expect, actual ) * * You do not have direct access to the private array data in IntArrayBag. * We provide the countOccurrences(Integer) method to help you test if * the add(Integer) method correctly adds elements to data. * * There are examples of above methods in testEnsureCapacity */ public void testAdd() { } }