Java面试题之手写ArrayList

Posted 2022-11-30 桓桓桓桓

package com.xingtu.sdk.sdk;

public class MyArrayList<T> 

    private T[] array;
    private int theSize;

    public MyArrayList()
        this(10);
    

    private MyArrayList(int length)
        try 
            new Exception();
        catch (Exception e)
            e.printStackTrace();
        
        array = (T[]) new Object[length];
    

    /**
     * 添加元素
     * @param t
     * @return
     */
    public boolean add(T t)
        add(size(),t);
        return true;
    

    /**
     * 在对应位置添加元素
     * @param idx
     * @param t
     */
    private void add(int idx,T t)
        if (array.length == size())
            //扩容
            ensureCapacity(size() * 2 + 1);
        
        if (idx > size())
            idx = size();

        array[idx] = t;
        if (idx >= size()) 
            theSize++;
        
    

    /**
     * List扩容
     * @param newSize
     */
    private void ensureCapacity(int newSize)
        if (newSize < size())
            return;
        
        T[] ot = array;
        array = (T[]) new Object[newSize];
        for (int i = 0;i < ot.length;i++)
            array[i] = ot[i];
        
    

    /**
     * 移除元素
     * @param idx
     * @return
     */
    public T reomve(int idx)
        T removedItem = array[idx];
        for(int i = idx; i < size()-1; i++) //为什么不是size()
            array[i] = array[i + 1];
        
        theSize--;
        return removedItem;
    

    /**
     * 设置某位置元素
     * @param idx
     * @param newVal
     * @return
     */
    public T set(int idx,T newVal)
        if(idx < 0 || idx >= size())
            return null;
        else
            T old = array[idx];
            array[idx] = newVal;
            return old;
        
    

    /**
     * 获取List长度
     * @return
     */
    public int size()
        return theSize;
    

    /**
     * 判断List是否为空
     * @return
     */
    public boolean isEmpty()
        return size() == 0;
    

    /**
     * 获取对应下标元素
     * @param idx
     * @return
     */
    public T get(int idx)
        if(idx < 0 || idx >= size())
            return null;
        else
            return array[idx];
        
    

    public static void main(String[] args)
        MyArrayList<String> list = new MyArrayList<>();
        int size = list.size();
        System.out.println("size1 = "+ size);
        list.add("1");
        list.add("2");
        list.add("3");
        System.out.println("size2 = "+ list.size());
        list.reomve(0);
        System.out.println("size3 = "+ list.size());