这样的向下转型如何不报运行时错误ClassCastException

class OutContent {    int m = 0;    public void output(NodeList nodeList) {        int size = nodeList.getLength();        for (int k = 0; k < size; k++) {            Node node = nodeList.item(k);            if (node.getNodeType() == Node.TEXT_NODE) {                                //父类型Node强转成子类型Text，怎么不报错？                Text textNode = (Text) node;                String content = textNode.getWholeText();                m++;                System.out.print(content);            }            if (node.getNodeType() == Node.ELEMENT_NODE) {                                //这里也是样的问题                Element elementNode = (Element) node;                String name = elementNode.getNodeName();                System.out.print(name);                NodeList nodes = elementNode.getChildNodes();                output(nodes);            }        }    }

package com.test;class A {    void aMthod() {        System.out.println("A method");    }}class B extends A {    void bMethod1() {        System.out.println("B method 1");    }    void bMethod2() {        System.out.println("B method 2");    }}public class C {    public static void main(String[] args) {        A a2 = new A();        B b2 = (B) a2; // 向下转型，编译无错误，运行时将出错        b2.aMthod();        b2.bMethod1();        b2.bMethod2();    }}