Java简单实现MapReduce列表

SimpleList.java

package net.gerhut.functionaljava;

import java.lang.reflect.Array;
import java.util.Arrays;

public class SimpleList<E> {

	public static interface SingleArgFunction<E> {
		E apply(E arg);
	}

	public static interface DoubleArgsFunction<E> {
		E apply(E arg1, E arg2);
	}

	private E[] entries;
	private int length;

	public SimpleList(E ...args) {
		entries = args;
		length = entries.length;
	}

	public SimpleList<E> map(SingleArgFunction<E> func) {
		SimpleList<E> result = new SimpleList<E>();
		if (length > 0) {
			E[] resultEntries = (E[])Array.newInstance(entries.getClass().getComponentType(), length);
			for (int i = 0, l = entries.length; i < l; i++)
				resultEntries[i] = func.apply(entries[i]);
			result.entries = resultEntries;
			result.length = length;
		}
		return result;
	}

	public E reduce(DoubleArgsFunction<E> func) {
		E result = null;
		if (length > 0) {
			result = entries[0];
			for (int i = 1, l = entries.length; i < l; i++)
				result = func.apply(result, entries[i]);
		}
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof SimpleList)) return false;
		return Arrays.equals(entries, ((SimpleList<E>)obj).entries);
	}

	@Override
	public int hashCode() {
		int code = 0;
		for (int i = 0, l = entries.length; i < l; i++)
			code += entries[i].hashCode();
		return code;
	}
	
	@Override
	public String toString() {
		if (length > 0) {
			StringBuilder sBuilder = new StringBuilder();
			for (int i = 0, l = entries.length; i < l; i++) {
				sBuilder.append(sBuilder.length() == 0 ? "[": ", ");
				sBuilder.append(entries[i]);
			}
			return sBuilder + "]";
		} else {
			return "Nil";
		}
	}

	public static void main(String args[]) {
		SimpleList<Integer> sl = new SimpleList<Integer>(1, 2, 3, 4, 5);
		System.out.println(sl.map(new SingleArgFunction<Integer>() {
			@Override
			public Integer apply(Integer args) {
				return args * args;
			}
		}).reduce(new DoubleArgsFunction<Integer>() {
			@Override
			public Integer apply(Integer arg1, Integer arg2) {
				return arg1 + arg2;
			}
		}));
	}
}