Java泛型模拟scala实现自定义ArrayList方式

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

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

 import java.util.ArrayList; //泛型类 public class MyList extends ArrayList { //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  MyList map(Function1 fun){ MyList 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 filter(Function1 fun){ MyList 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 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 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 { 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  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 - 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()); } }