ArrayList.java

package list;

import org.junit.Test;

import java.util.Arrays;
import java.util.NoSuchElementException;

/**
 * Created by william on 2017/2/25.
 */
public class ArrayList<T> implements List<T> {
    private static final int DEFAULT_CAPACITY = 10;
    private int size;
    private Object[] elementData;

    public ArrayList() {
        elementData = new Object[DEFAULT_CAPACITY];
    }

    public ArrayList(int initialCapacity) {
        if (initialCapacity < 0)
            throw new RuntimeException("非法初始化大小参数!");
        elementData = new Object[initialCapacity];
    }

    public ArrayList(T[] array) {
        if (array == null)
            throw new NullPointerException();
        elementData = array;
    }

    public boolean add(T ele) {
        grow(size);
        elementData[size++] = ele;
        return true;
    }

    public T get(int index) {
        checkBounds(index, false);
        return (T) elementData[index];
    }

    public T remove(int index) {
        checkBounds(index, false);
        T removeEle = (T) elementData[index];
        System.arraycopy(elementData, index + 1, elementData, index, size - index);
        size--;
        return removeEle;
    }

    public boolean add(int index, T ele) {
        checkBounds(index, true);
        grow(size++);
        //将原本数组从待插入的index截取，将原本index后的有效值，复制到原本数组index+1之后
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = ele;
        return true;
    }


    @Override
    public boolean remove(T ele) {
        int index;
        if ((index = indexOf(ele)) == -1)
            return false;
        remove(index);
        return true;
    }

    private void checkBounds(int index, boolean isAdd) {
        if (isAdd && (index < 0 || index > size)) {
            throw new IndexOutOfBoundsException("index : " + index + ", size : [ 0 - " + size + " ]");
        } else if (!isAdd && (index < 0 || index >= size))
            throw new IndexOutOfBoundsException("index : " + index + ", size : [ 0 - " + size + " ]");
    }

    public int size() {
        return size;
    }

    private void grow(int miniCapacity) {
        if (miniCapacity >= elementData.length) {
            int oldCapacity = elementData.length;
            int newCapacity = oldCapacity + (oldCapacity >> 1) > Integer.MAX_VALUE ? Integer.MAX_VALUE : oldCapacity + (oldCapacity >> 1);
            if (newCapacity - miniCapacity < 0)
                newCapacity = miniCapacity > Integer.MAX_VALUE ? Integer.MAX_VALUE : miniCapacity;
            elementData = Arrays.copyOf(elementData, newCapacity);
        }
    }

    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public boolean contains(T ele) {
        return indexOf(ele) != -1;
    }

    public int indexOf(T ele) {
        for (int i = 0; i < size; i++) {
            if ((ele == null && elementData[i] == null) || (ele.equals(elementData[i])))
                return i;
        }
        return -1;
    }

    @Override
    public boolean addAll(List<T> l) {
        Object[] eles = l.toArray();
        grow(eles.length + size);
        System.arraycopy(eles, 0, elementData, size, eles.length);
        return true;
    }

    @Override
    public Object[] toArray() {
        return Arrays.copyOf(elementData, size);
    }


    public Iterator<T> iterator() {
        return new Itr<T>();
    }

    private class Itr<T> implements Iterator<T> {
        int cursor;//待遍历元素的下标

        @Override
        public boolean hasNext() {
            return cursor != size;
        }

        @Override
        public T next() {
            if (cursor >= size)
                throw new NoSuchElementException();
            return (T) elementData[cursor++];
        }

        @Override
        public void remove() {
            if (cursor >= size)
                throw new NoSuchElementException();
            ArrayList.this.remove(cursor--);
        }
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("[ ");
        for (Object ele : elementData) {
            sb.append(ele).append(" ");
        }
        return sb.append("]").toString();
    }
}