自己实现一个简单的ArrayList

Posted 2021-03-18 esrevinud

参考接口

public interface myList<T> {
    void add(T element);
    void add(Integer index, T element);
    T remove(Integer index);
    Boolean contains(T element);
    Integer size();
    Integer indexOf(T element);
    Integer lastIndexOf(T element);
    void set(Integer index, T element);
    T get();
    T get(Integer index);
    Boolean clear();
    Boolean isEmpty();
}

实现代码

package learn.code.list;

public class MyArrayList<T> implements myList<T> {

    private T[] core;
    private int size;

    private void resize(int capacity) {
        T[] newCore = (T[]) new Object[capacity];
        for (int i = 0; i < core.length; i ++) {
            newCore[i] = core[i];
        }
        core = newCore;
    }

    public MyArrayList () {
        this(10);
    }

    public MyArrayList (int capacity) {
        core = (T[]) new Object[capacity];
        size = 0;
    }

    @Override
    public void add(T element) {
        if (size == core.length) {
            //  扩容原先的2倍
            this.resize(core.length * 2);
        }
        core[size] = element;
        size ++;
    }

    // 指定下标位置插入，不能跳跃当前最后的下标
    @Override
    public void add(Integer index, T element) {
        if (index < 0 || index >= core.length) {
            throw new IndexOutOfBoundsException("下标不能小于0");
        }

        if (index >= core.length) {
            throw new IndexOutOfBoundsException("下标超出当前数组");
        }
        core[index] = element;
        size ++;
    }

    @Override
    public T remove(Integer index) {
        T removeTarget = core[index];
        for (int i = index; i < (size - 1); i ++) {
            core[index] = core[index + 1];
        }
        size --;
        return removeTarget;
    }

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

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

    @Override
    public Boolean contains(T element) {
        for (T e : this.core) {
            if (e == element) {
                return true;
            }
        }
        return false;
    }

    @Override
    public Integer size() {
        return this.size;
    }

    //  找到就返回下标，没找到就返回-1
    @Override
    public Integer indexOf(T element) {
        for (int i = 0; i < core.length; i ++) {
            if (core[i] == element) {
                return i;
            }
        }
        return -1;
    }

    // indexOf的逆序版
    @Override
    public Integer lastIndexOf(T element) {
        for (int i = core.length - 1; i >= 0; i --) {
            if (core[i] == element) {
                return i;
            }
        }
        return -1;
    }

    @Override
    public void set(Integer index, T element) {
        if (index < 0 || index >= core.length) {
            throw new IndexOutOfBoundsException("下标不能小于0");
        }

        if (index >= core.length) {
            throw new IndexOutOfBoundsException("下标超出当前数组");
        }

        core[index] = element;
    }

    // 软删除， 不删除实际元素
    @Override
    public Boolean clear() {
        size = 0;
        return null;
    }

    @Override
    public Boolean isEmpty() {
        return size == 0;
    }
    @Override
    public T get() {
        return core[size - 1];
    }
    @Override
    public T get(Integer index) {
        return core[index];
    }

    public static void main(String[] args) {
        MyArrayList<Integer> arr = new MyArrayList<>();
        for (int i = 0; i < 10; i ++) {
            arr.add(10 - i);
        }
//        arr.set(0, 666);
//        arr.remove(2);
        arr.removeLast();
        arr.clear();
        for (int i = 0; i < arr.size(); i ++) {
            System.out.println(arr.get(i));
        }
        System.out.println(arr.isEmpty());

    }
}