结合源码手写ArrayList

1.项目结构

 2.定义接口

package list;

public interface MyList<E> {
    public abstract void add(E object);

    public abstract void add(int index, E object);

    public abstract boolean remove(E object);

    public abstract Object remove(int index);

    public abstract int getSize();

    public abstract Object get(int index);

    public abstract void set(int index, Object object);
}

1. 3.定义实现类

package list;

import java.util.Arrays;

public class MyArrayList<E> implements MyList {
　　　　//定义数组
    private transient Object[] elementData;
　　　　//元素个数
    private int size;
　　//构造方法初始化数组容量
    public MyArrayList() {
        this(10);
    }
　　　
    public MyArrayList(int initialCapacity) {
        if (initialCapacity < 0) {
            throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
        }
        elementData = new Object[initialCapacity];
    }

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

    //数组扩容
    private void ensurExplicitVapacity(int minCapacity) {
        if (minCapacity > elementData.length) {
            int oldCapacity = elementData.length;
            int newCapacity = oldCapacity + (oldCapacity >> 1);
            elementData = Arrays.copyOf(elementData, newCapacity);
        }
    }

    @Override
    public void add(int index, Object object) {
        rangeCheck(index);
        ensurExplicitVapacity(size + 1);
        System.arraycopy(elementData, index, elementData, index + 1, size);
        elementData[index] = object;
        size++;
    }

    //检测数组是否索引越界
    private void rangeCheck(int index) {
        if (index >= size || index < 0) {
            throw new IndexOutOfBoundsException("lenth-->" + index);
        }
    }

    @Override
    public boolean remove(Object object) {
        for (int i = 0; i < elementData.length; i++) {
            Object element = elementData[i];
            if (element.equals(object)) {
                remove(i);
                return true;
            }
        }
        return false;

    }

    @Override
    public Object remove(int index) {
        Object object = get(index);
        int numMoved = elementData.length - index - 1;
        if (numMoved > 0) {
            System.arraycopy(elementData, index + 1, elementData, index, numMoved);
        }
        elementData[--size] = null;
        return object;
    }

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

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

    @Override
    public void set(int index, Object object) {
        rangeCheck(index);
        remove(index);
        E e = (E) object;
        add(index, e);
    }
}

4.定义测试类

package list;

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        MyArrayList<String> list = new MyArrayList<>();
        for (int i = 0; i < 100; i++) {
            list.add(i + "");
        }
        list.add(0, "按照索引添加元素");
        list.add(0, "fff");
        printList(list);
        //list.remove("fff");
        //list.remove(0);
        list.set(0,"set");
        printList(list);

    }
　　　//遍历打印
    public static void printList(MyArrayList<String> list) {
        System.out.print("[");
        for (int i = 0; i < list.getSize(); i++) {
            if (i != list.getSize()) {
                System.out.print(list.get(i) + ", ");
            } else {
                System.out.print(list.get(i) + "]");
            }
        }
    }
}

5.总结

　　Arraylist源码难点 : 数组是如何扩容的

　　这里只是写了一些Arraylist的简单逻辑, 还有很多细节没有去实现,编写这段代码只是为了更好的理解ArrayList的实现原理

　　立志终生学习

　　原文来源: https://blog.csdn.net/sonwing_for/article/details/81751072