package?com.imooc;
import?java.util.HashMap;
import?java.util.Map;
public?class?Test1?{
public?Map?<Integer,String>?two;?
public?Test1(){
Map?two?=new?HashMap<String,String>();
}
public?void?student(){
?????String?one2="nihao";
???
???? ?two.put(3,?one2);
???? ?System.out.println(two.get(3));
??????????
}
????public?static?void?main(String[]?args)?{
???? Test1?one=new?Test1();
?????one.student();
?
?
?
}
}請問這段代碼為什么會運行時異常，有人說是空指針異常?？晌颐髅髟趖wo調用put（）方法添加進去了鍵值對啊。
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