关于java中的值传递与引用传递遇到的问题

来源于：https://www.nowcoder.com/test/question/done?tid=14302398&qid=25373#summary

下列java程序的输出结果为____。

public class Example{
    String str=new String("hello");
    char[]ch={'a','b'};
    public static void main(String args[]){
        Example ex=new Example();
        ex.change(ex.str,ex.ch);
        System.out.print(ex.str+" and ");
        System.out.print(ex.ch);
    }
    public void change(String str,char ch[]){
        str="test ok";
        ch[0]='c';
    }
}

正确答案: B   你的答案: E (错误)

hello and ab

hello and cb

hello and a

test ok and ab

test ok and cb

test ok and c