结合源码手写ArrayList

1.项目结构

2.定义接口

 1 package list;
 2 
 3 public interface MyList<E> {
 4     public abstract void add(E object);
 5 
 6     public abstract void add(int index, E object);
 7 
 8     public abstract boolean remove(E object);
 9 
10     public abstract Object remove(int index);
11 
12     public abstract int getSize();
13 
14     public abstract Object get(int index);
15 
16     public abstract void set(int index, Object object);
17 }

3.定义实现类

 1 package list;
 2 
 3 import java.util.Arrays;
 4 
 5 public class MyArrayList<E> implements MyList {
　　　　//定义数组
 6     private transient Object[] elementData;
　　　　//元素个数
 7     private int size;
 8 　　//构造方法初始化数组容量
 9     public MyArrayList() {
10         this(10);
11     }
12 　　　
13     public MyArrayList(int initialCapacity) {
14         if (initialCapacity < 0) {
15             throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
16         }
17         elementData = new Object[initialCapacity];
18     }
19 
20     @Override
21     public void add(Object object) {
22         ensurExplicitVapacity(size + 1);
23         elementData[size++] = object;
24     }
25 
26     //数组扩容
27     private void ensurExplicitVapacity(int minCapacity) {
28         if (minCapacity > elementData.length) {
29             int oldCapacity = elementData.length;
30             int newCapacity = oldCapacity + (oldCapacity >> 1);
31             elementData = Arrays.copyOf(elementData, newCapacity);
32         }
33     }
34 
35     @Override
36     public void add(int index, Object object) {
37         rangeCheck(index);
38         ensurExplicitVapacity(size + 1);
39         System.arraycopy(elementData, index, elementData, index + 1, size);
40         elementData[index] = object;
41         size++;
42     }
43 
44     //检测数组是否索引越界
45     private void rangeCheck(int index) {
46         if (index >= size || index < 0) {
47             throw new IndexOutOfBoundsException("lenth-->" + index);
48         }
49     }
50 
51     @Override
52     public boolean remove(Object object) {
53         for (int i = 0; i < elementData.length; i++) {
54             Object element = elementData[i];
55             if (element.equals(object)) {
56                 remove(i);
57                 return true;
58             }
59         }
60         return false;
61 
62     }
63 
64     @Override
65     public Object remove(int index) {
66         Object object = get(index);
67         int numMoved = elementData.length - index - 1;
68         if (numMoved > 0) {
69             System.arraycopy(elementData, index + 1, elementData, index, numMoved);
70         }
71         elementData[--size] = null;
72         return object;
73     }
74 
75     @Override
76     public int getSize() {
77         return size;
78     }
79 
80     @Override
81     public Object get(int index) {
82         rangeCheck(index);
83         return elementData[index];
84     }
85 
86     @Override
87     public void set(int index, Object object) {
88         rangeCheck(index);
89         remove(index);
90         E e = (E) object;
91         add(index, e);
92     }
93 }

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