动态数组（java）

package arraList;

public interface AbstractArray<E> {
    int size();//元素数量
    boolean isEmpty();//是否为空
    boolean contains(E element);//是否包含某个元素
    void add(E element);//添加元素到最后面
    E get(int index);//返回index位置对应的元素
    E set(int index,E element);//设置index位置的元素
    void add(int index,E element);//往index位置添加元素
    E remove(int index);//删除index位置对应的元素
    int indexOf(E element);//查看元素的位置
    void clear();//清除所有元素
}

package arraList;

public class ArrayList<E> implements AbstractArray<E> {
    private int size;
    private E[] elements;
    private static final int DEFAULT_CAPACITY = 10;
    private static final int ELEMENT_NOT_FOUND = -1;
    public ArrayList(int capacity){
        capacity = (capacity < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY :capacity;
        elements =(E[]) new Object[capacity];
    }
    public ArrayList(){
        this(DEFAULT_CAPACITY);
    }
    @Override
    public int size() {
        return size;
    }

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

    @Override
    public boolean contains(E element) {
        return indexOf(element) != ELEMENT_NOT_FOUND;
    }

    @Override
    public void add(E element) {
        add(size,element);
    }
    @Override
    public E get(int index) {
        rangeCheck(index);
        return elements[index];
    }

    @Override
    public E set(int index, E element) {
        rangeCheck(index);
        E old = elements[index];
        elements[index] = element;
        return old;
    }

    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);
        ensureCapacity(size + 1);
        for(int i = size - 1;i >= index;i --){
            elements[i + 1] = elements[i];
        }
        elements[index] = element;
        size ++;
    }

    @Override
    public E remove(int index) {
        E old = elements[index];
        for (int i = index + 1; i <= size; i++) {
            elements[i - 1] =  elements[i];
        }
        elements[--size] = null;
        return old;
    }

    @Override
    public int indexOf(E element) {
        if(element == null){
            for (int i = 0; i < size; i++) {
                if(elements[i] == null)return i;
            }

        }else{
            for (int i = 0; i < size; i++) {
                if(element.equals(elements[i])) return i;
            }
        }

        return ELEMENT_NOT_FOUND;
    }

    @Override
    public void clear() {
        for (int i = 0; i < size; i++) {
            elements[i] = null;
        }
        size = 0;
    }
    private void ensureCapacity(int capacity){
        int oldCapacity = elements.length;
        if(oldCapacity >= capacity) return;

        int newCapacity = oldCapacity + (oldCapacity >> 1);
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i]  = elements[i];
        }
        elements = newElements;

    }
    private void rangeCheckForAdd(int index){
        if(index < 0 || index > size) throw new IndexOutOfBoundsException("Index:"+ index +",Size"+size);
    }
    private void rangeCheck(int index){
        if(index < 0 || index >= size) throw new IndexOutOfBoundsException("Index:"+ index +",Size" + size);
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        for (int i = 0; i < size; i++) {
            if(i != 0){
                string.append(", ");
            }
            string.append(elements[i]);
        }
        string.append("]");
        return string.toString();
    }
}

测试

public class test {
    @Test
    public void test(){
        ArrayList<Integer> lists = new ArrayList<>();
        lists.add(1);
        lists.add(2);
        System.out.println(lists);
        
        ArrayList<Person> persons = new ArrayList<>();
        persons.add(new Person("jack",10));
        persons.add(new Person("james",21));
        persons.add(new Person("rose",18));
        persons.add(null);
        System.out.println(persons);

        System.out.println(persons.indexOf(null));
    }
}

重点：

• 动态数组的扩容机制
• 泛型
• indexOf() 方法判断是否相等，equals() 和 == 区别
• 添加、删除：移动元素

 

原文地址：https://blog.csdn.net/woai3364/article/details/140247326

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