数据结构笔记_动态数组的实现

public class Array<E> {
    private E[] data;
    private int size;

    public Array(int capacity){
        data = (E[])new Object[capacity];  //不能直接new一个泛型数组，需要先new一个Object数组再强转为泛型数组。
    }
    public Array(){
        this(10);
    }

    public int getSize(){
        return size;
    }

    public int getCapacity(){
        return data.length;
    }

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

    public void add(int index, E e){
        if (index <0 || index>size){
            throw new IllegalArgumentException("Add failed! Require index>=0 and index<=size.");
        }

        if (size==data.length){
            resize(2*data.length);
        }

        for (int i=size-1; i>=index; i--){
            data[i+1]=data[i];
        }
        data[index]=e;
        size++;
    }

    public void addFirst(E e){
        add(0,e);
    }

    public void addLast(E e){
        add(size,e);
    }

    public E get(int index){
        if (index<0 || index>=size){
            throw new IllegalArgumentException("Get failed! Index is illegal.");
        }

        return data[index];
    }

    public void set(int index, E e){
        if(index<0 || index>=size){
            throw new IllegalArgumentException("Set failed! Index is illegal.");
        }

        data[index]=e;
    }

    public boolean contains(E e){
        for (int i=0; i<size; i++){
            if (data[i].equals(e)){
                return true;
            }
        }
        return false;
    }

    public int find(E e) {
        for (int i=0; i<size; i++){
            if(data[i].equals(e)){
                return i;
            }
        }
        return -1;
    }

    //删除索引为index的元素，并返回被删除的元素
    public E remove(int index){
        if(index<0 || index>=size){
            throw new IllegalArgumentException("Remove failed! Index is illegal.");
        }

        E ret=data[index];
        for (int i=index+1; i<size; i++){
            data[i-1]=data[i];    //尽量不要使用data[i]=data[i+1] i+1可能会发生数组越界
        }
        size--;
        data[size]=null;  //无用的游离状态元素

        if(size==data.length/4 && data.length/2!=0){   //采用更lazy的方法，防止在size=capacity时来回加减元素时发生复杂度震荡的情况。
            resize(data.length/2);
        }

        return ret;
    }

    public E removeFirst(){
        return remove(0);
    }

    public E removeLast(){
        return remove(size-1);
    }

    public void removeElement(E e){
        int index=find(e);
        if(index!=-1){
            remove(index);
        }
    }

    //实现动态数组
    private void resize(int newCapacity){
        E[] newData=(E[])new Object[newCapacity];
        for(int i=0; i<size; i++){
            newData[i]=data[i];
        }
        data=newData;  //newData在函数退出后会被回收，data是全局变量，生存周期和类一样
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("Array: size: %d, capacity: %d\n",size, data.length));
        res.append("[");
        for (int i=0; i<size; i++){
            res.append(data[i]);
            if (i!=size-1){
                res.append(", ");
            }
        }
        res.append("]");
        return res.toString();
    }
}
数据结构笔记_动态数组的实现

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