List集合-ArrayList

实现思路:

1.初始化一个Object[] 的数据，在构造函数中默认空的数组，在add()方法中new出空间。初始size为10.

2.(核心)底层利用Arrays.copyOf()方法进行扩容处理，每次扩展容量的一半。

3.指定添加位置时，利用System.arraycopy()方法将之后的元素统一向后移动一位，最后在插入。

git上项目路径: https://github.com/0ziyu0/handWriting

代码：

接口

public interface CustomerList<E> {
    
    public void add(E object);
    
    public void add(int index, E object);
    
    public Object get(int index);
    
    public Object remove(int index);
    
    public Boolean remove(E object);
    
    public int size();
}

实现

public class CustomerArrayList<E> implements CustomerList<E> {
    
    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
    
    private static final Object[] EMPTY_ELEMENTDATA = {};
    
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
    
    private transient Object[] elementData;
    
    private int size;
    
    private static final int DEFAULT_CAPACITY = 10;
    
    public CustomerArrayList() {
        // 默认是空数组
//        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
        this.elementData = new Object[DEFAULT_CAPACITY];
    }
    
    public CustomerArrayList(int initialCapacity) {
        
        if(initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if(initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("数组参数初始化错误...");
        }
        
    }
    
    // 进行扩容处理
    private void ensureCapacityInternal(int minCapacity) {
        
        if(size == elementData.length) {
            int newCapacity = size + size >> 1;// 扩容一半
            if(newCapacity < minCapacity) { // 防止初始化容器为1的情况下,上述位移运算后扩容大小与原大小一样
                newCapacity = minCapacity;
            }
            elementData = Arrays.copyOf(elementData, newCapacity);
        }
        
    }
    
    public void checkBorder(int index) {
        if(index >= size || index < 0) {
            throw new RuntimeException("数组越界...");
        }
    }

    @Override
    public void add(E object) {
        
        ensureCapacityInternal(size + 1);
        elementData[size++] = object;
        
    }

    @Override
    public void add(int index, E object) {
        
        checkBorder(index);
        ensureCapacityInternal(size + 1);
        // 将index后面的值全部向后移动一位,然后插入新值
        int removeIndex = size - index; 
        if(removeIndex > 0) {
            System.arraycopy(elementData, index, elementData, index + 1, removeIndex);
        }
        elementData[index] = object;
        size++;
    }

    @Override
    public Object get(int index) {
        
        checkBorder(index);
        
        return elementData[index];
    }

    @Override
    public Object remove(int index) {
        
        checkBorder(index);
        // 将index后面的值向前移动一位,将最后一位置为null,size减1
        Object removeObj = elementData[index];
        int removeIndex = elementData.length - index - 1;
        if(removeIndex > 0) {
            System.arraycopy(elementData, index + 1, elementData, index, removeIndex);
        }
        elementData[--size] = null;
        return removeObj;
    }

    @Override
    public Boolean remove(E object) {
        
        try {
            for(int i = 0; i < size; i++) {
                if(object.equals(elementData[i])) {
                    remove(i);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException();
        }
        
        return true;
    }

    @Override
    public int size() {
        
        return size;
    }
    
    
}

测试代码

public class ListTest {

    @Test
    public void testArrayListAdd001() {
        
        CustomerList<String> list = new CustomerLinkedList<String>();
        list.add("test1");
        list.add("test2");
        list.add("test3");
        
        print(list);
        list.remove(1);
        print(list);
    }
    
    @Test
    public void testArrayListAdd002() {
        
        CustomerList<String> list = new CustomerLinkedList<String>();
        list.add("test1");
        list.add("test2");
        list.add("test3");
        
        print(list);
        
        list.add(0, "test0");
        print(list);
        
    }
    
    @Test
    public void testRemove001() {
        
        CustomerList<String> list = new CustomerLinkedList<String>();
        list.add("test1");
        list.add("test2");
        list.add("test3");
        
        print(list);
        
        list.remove(1);
        print(list);
        
    }
    
    @Test
    public void testRemove002() {
        
        CustomerList<String> list = new CustomerLinkedList<String>();
        list.add("test1");
        list.add("test2");
        list.add("test3");
        
        print(list);
        
        list.remove("test2");
        print(list);
        
    }
    
    @Test
    public void testSize001() {
        
        CustomerList<String> list = new CustomerLinkedList<String>();
        list.add("test1");
        list.add("test2");
        list.add("test3");
        
        System.out.println(list.size());
        
    }
    
    private void print(CustomerList<String> list) {
        System.out.println("=======");
        for(int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }
    
}

运行截图