关于Map的引用测试

package com.cpic.model.testswitch;import java.util.HashMap;import java.util.Map;public class TestSubString {public static void main(String[] args) {Map<String, String> resultMap=new HashMap<String, String>();copyMap(resultMap);System.out.println(resultMap.get("KEY"));}private static void copyMap( Map<String, String> resultMap){//resultMap=returnMap();  //AresultMap.putAll(returnMap());  //B}private static Map<String, String> returnMap(){Map<String, String> test=new HashMap<String, String>();test.put("KEY", "TEST");return test;}}

走A时输出：null

使用B时输出：TEST