将条目从一个映射复制到另一个映射，并删除目标映射中源映射中的值为空的条目。

//package com.nowjava;/** 来自 时 代 J     a    v  a - nowjava.com**/


import java.util.Map;


public class Main {

    /**

     * Copies entries from one map to another and deletes those entries in the target map for which

     * the value in the source map is null.<p>

     * 

     * @param <A> the key type of the map 

     * @param <B> the value type of the map 

     * @param source the source map

     * @param target the target map 

     */

    public static <A, B> void updateMapAndRemoveNulls(Map<A, B> source,

            Map<A, B> target) {


        assert source != target;

        for (Map.Entry<A, B> entry : source.entrySet()) {

            A key = entry.getKey();

            B value = entry.getValue();

            if (value != n