Java泛型模拟scala实现自定义ArrayList方式

//泛型接口
public interface Function1<T, R> { 
    R call(T t); 
}

//泛型接口
public interface Function2<E> { 
    E call(E elem,E sum); 
}

import java.util.ArrayList; 
//泛型类
public class MyList<E> extends ArrayList<E> { 
    //泛型方法  （只有在public修饰符和返回值之间用了泛型的才是泛型方法，指定后，该方法内可以使用该泛型）
    public <R> MyList<R> map(Function1<E, R> fun){
        MyList<R> myList = new MyList<>();
        for (E e : this) {
            R res = fun.call(e);
            myList.add(res);
        }
        return myList;
    }
 
    //这个不是泛型方法，泛型在引用时指定，可以是泛型类中已经定义的，也可以是具体的类
    public MyList<E> filter(Function1<E,Boolean> fun){
        MyList<E> myList = new MyList<>();
        for(E elem : this){
            Boolean flag = fun.call(elem);
            if(flag){
                myList.add(elem);
            }
        }
        return myList;
    }
 
    //这个也不是泛型方法
    public E reduce(Function2<E> fun){
        E sum = null;
        boolean isFirst = true;
        for (E elem : this) {
            if(isFirst){
               sum =  elem;
               isFirst = false;
            }else {
                sum = fun.call(elem,sum);
            }
        }
        return sum;
    } 
}

public class MyTest { 
    public static void main(String[] args) { 
        MyList<String> myList = new MyList<>();
        myList.add("aaaa");
        myList.add("bbbb");
        myList.add("cccc");
        myList.add("accc");
 
        String res = myList.filter(x -> x.contains("a")).map(x -> x.toUpperCase()).reduce((x, y) -> x + y);
        System.out.println(res);
    }
}

/**
 * 自定义实现ArrayList
 */
public class TextArrayList<E> {
    private Object[] elementData;
    private int size;
    private static final int DEFALT_CAPACITY = 10;
    /**
     * 无参构造，默认数组大小为10
     */
    public TextArrayList() {
        elementData = new Object[DEFALT_CAPACITY];
    }
    /**
     * 有参构造，数组大小为传入的值
     */
    public TextArrayList(int capacity) {
        if (capacity < 0) {
            throw new RuntimeException("容器容量不能为负数");
        } else if (capacity == 0) {
            elementData = new Object[DEFALT_CAPACITY];
        } else {
            elementData = new Object[capacity];
        }
    }
    /**
     * 给数组中添加元素
     *
     * @param element */
    public void add(E element) {
        //数组扩容
        if (size == elementData.length) {
            Object[] newArray = new Object[elementData.length + (elementData.length >> 1)];
            System.arraycopy(elementData, 0, newArray, 0, elementData.length);
            elementData = newArray;
        }
        elementData[size++] = element;
    }
    /**
     * 删除元素
     * 挨个比较所有元素，获得第一个比较结果为True的，返回
     *
     * @return
     */
    public void remove(E element) {
        for (int i = 0; i < size; i++) {
            if (element.equals(get(i))) {
                //比较操作用到equals方法
                System.arraycopy(elementData, i + 1, elementData, i, elementData.length - i - 1);
                elementData[size - 1] = null;
                size--;
            }
        }
    }
    /**
     * 删除索引
     *
     * @return
     */
    public void remove(int index) {
        int numMoved = elementData.length - index - 1;
        if (numMoved > 0) {
            System.arraycopy(elementData, index + 1, elementData, index, numMoved);
        }
        elementData[size - 1] = null;
        size--;
    }
    /**
     * 判空
     *
     * @return
     */
    public boolean isEmpty() {
        return size == 0 ? true : false;
    }
    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        //[a,b,c]
        stringBuilder.append("[");
        for (int i = 0; i < size; i++) {
            stringBuilder.append(elementData[i] + ",");
        }
        stringBuilder.setCharAt(stringBuilder.length() - 1, ']');
        return stringBuilder.toString();
    }
    /**
     * 增加get方法
     *
     * @param index
     */
    public E get(int index) {
        checkRange(index);
        return (E) elementData[index];
    }
    /**
     * 增加set方法
     *
     * @param index
     */
    public void set(E element, int index) {
        checkRange(index);
        elementData[index] = element;
    }
    //判断索引合法性
    public void checkRange(int index) {
        if (index < 0 || index > size - 1) {
            throw new RuntimeException("索引不合法:" + index);
        }
    }
    public static void main(String[] args) {
        TextArrayList t1 = new TextArrayList(20);
//        t1.add("aa");
//        t1.add("bb");
        for (int i = 0; i < 40; i++) {
            t1.add("wang" + i);
        }
        t1.set("sss", 10);
        System.out.println(t1);
        System.out.println(t1.get(39));
        t1.remove(3);
        t1.remove("wang5");
        System.out.println(t1);
        System.out.println(t1.size);
        System.out.println(t1.isEmpty());
    }
}