ArrayList.java

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1/*2 * ArrayList.java3 *4 * Computer Science S-22, Harvard University5 */6 7import java.util.*;8 9/*10 * A class that implements our simple List interface using an array.11 */12public class ArrayList implements List {13    private Object[] items;     // the items in the list14    private int length;         // # of items in the list15    16    /*17     * Constructs an ArrayList object with the specified maximum size18     * for a list that is initially empty.19     */20    public ArrayList(int maxSize) {21        if (maxSize <= 0) {22            throw new IllegalArgumentException("max size must be positive");23        }24        items = new Object[maxSize];25        length = 0;26    }27    28    /*29     * Constructs an ArrayList object containing the items in the specified30     * array, and with a max size that is twice the size of that array 31     * (to allow room for growth).32     */33    public ArrayList(Object[] initItems) {34        items = new Object[2 * initItems.length];        35        for (int i = 0; i < initItems.length; i++) {36            items[i] = initItems[i];37        }38        39        length = initItems.length;40    }41    42    /*43     * length - returns the number of items in the list 44     */45    public int length() {46        return length;47    }48    49    /* 50     * isFull - returns true if the list is full, and false otherwise51     */52    public boolean isFull() {53        return (length == items.length);54    }55    56    /* getItem - returns the item at position i in the list */57    public Object getItem(int i) {58        if (i < 0 || i >= length) {59            throw new IndexOutOfBoundsException();60        }61        62        return items[i];63    }64    65    /* 66     * addItem - adds the specified item at position i in the list,67     * shifting the items that are currently in positions i, i+1, i+2,68     * etc. to the right by one.  Returns false if the list is full,69     * and true otherwise.70     */71    public boolean addItem(Object item, int i) {72        if (item == null || i < 0 || i > length) {73            throw new IllegalArgumentException();74        } else if (isFull()) {75            return false;76        }77        78        // make room for the new item79        for (int j = length - 1; j >= i; j--) {80            items[j + 1] = items[j];81        }82        83        items[i] = item;84        length++;85        return true;86    }87    88    /* 89     * removeItem - removes the item at position i in the list,90     * shifting the items that are currently in positions i+1, i+2,91     * etc. to the left by one.  Returns a reference to the removed92     * object.93     */94    public Object removeItem(int i) {95        if (i < 0 || i >= length) {96            throw new IndexOutOfBoundsException();97        }98        99        Object removed = items[i];100        101        // fill in the "hole" left by the removed item102        for (int j = i; j < length - 1; j++) {103            items[j] = items[j + 1];104        }105        items[length - 1] = null;106        107        length--;108        return removed;109    }110    111    /*112     * toString - converts the list into a String of the form 113     * {item0, item1, ...}114     */115    public String toString() {116        String str = "{";117        118        for (int i = 0; i < length; i++) {119            str = str + items[i];120            if (i < length - 1) {121                str = str + ", ";122            }123        }124        125        str = str + "}";126        return str;127    }128    129    /*130     * iterator - returns an iterator for this list131     */132    public ListIterator iterator() {133        // still needs to be implemented134        return null;135    }136}