Java與Scala創建List與Map的實現方式

//Java
List<String> languages = new ArrayList<>(); 
Map<String, Class> mapFields = new HashMap();
    
//Scala 
val languages = new util.ArrayList[String]    
val mapFields=new util.HashMap[String, Class]

package com.doit.udf;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
 * @author hulc
 * @slogan: just do it
 * @date 2020/9/13 21:16
 */
public class UserDefineFunc {
    public static void main(String[] args) {
        test1();
    }
    private static void test1() {
        // 使用java來實現scala中針對集合的map、reduce、filter函數的效果
        List<Integer> list = new ArrayList<>();
        list.addAll(Arrays.asList(1,2,3,4,5,6,7,8,9));
        MyList<Integer> integers = new MyList<Integer>(list);
        // 使用匿名內部類方式進行自定義map方法調用
        List<Object> list1 = integers.map(new MyMapFunction() {
            @Override
            public <String, K> String map(K k) {
                if (k instanceof Integer) {
                    Integer i = (Integer) k;
                    i += 10;
                    return (String) ("" + i);
                }
                return null;
            }
        });
        for (Object o : list1) {
            System.out.println(o.toString());
        }
    }
}
class MyList<T> extends ArrayList<T> {
    private List<T> words;
    public MyList(List<T> words) {
        this.words = words;
    }
    public List<Object> map(MyMapFunction function) {
        List<Object> ts = new ArrayList<>();
        for (T t : words) {
            Object map = function.map(t);
            ts.add(map);
        }
        return ts;
    }
}
interface MyMapFunction {
    // map就是一個轉換函數，輸入一個K，轉換為一個T
    <T, K> T map(K k);
}

private static void test2() {
        List<Integer> list = new ArrayList<>();
        list.addAll(Arrays.asList(1,2,3,4,5,6,7,8,9));
        // 將list轉換為Stream，再進行處理，這時候就可以使用函數式進行處理
        Stream<Integer> integerStream = list.stream();
        Stream<String> stringStream = integerStream.map(w -> {
            w += 10;
            return "" + w;
        });
        // 遍歷打印
        Object[] toArray = stringStream.toArray();
        for (Object o : toArray) {
            System.out.println(o.toString());
        }
    }