对象类型转换

【1】一个父类的引用类型变量可以指向其子类的对象；

【2】一个父类的引用不能访问其子类扩展的属性和方法；

【3】必须强制类型转换才可以访问。

 

 

 public class ObjectChangeTest {/** * function:test ObjectChange */public static void main(String[] args) {// TODO Auto-generated method stubPerson p=new Person("超人",100);Student st=new Student("小明",22,1001);Teacher tc=new Teacher("园丁",45,4600);//测试1：instanceof 来判断对象是否属于指定的类System.out.println(p instanceof Person); //trueSystem.out.println(st instanceof Student); //trueSystem.out.println(tc instanceof Teacher);//true//测试2：父类引用指向子类对象/** *【1】 在这里Person父类p引用指向子类Student对象 *【2】p引用能访问子类的name和age属性，即从Person类继承来的 *【3】但p引用不能访问子类Student扩展的属性no，要想访问，强制类型转换 */p=new Student("yy",22,100);System.out.println("p.name="+p.name);//p.name=yySystem.out.println("p.age="+p.age);//p.age=22//p引用为了访问子类的扩展属性，强制类型转换Student std=(Student)p;System.out.println("std.no="+std.no);//std.no=100Person ps=new Teacher("ss",56,2345);System.out.println("ps.name="+ps.name);//ps.name=ssSystem.out.println("ps.age="+ps.age);//ps.age=56Teacher tch=(Teacher)ps;System.out.println("tch.salary="+tch.salary);//tch.salary=2345.0//测试方法ObjectChangeTest test=new ObjectChangeTest();Person pp=new Person("人人",100);test.showInfo(pp); //name=人人,age=100System.out.println();test.showInfo(st);//name=小明,age=22,no=1001test.showInfo(tc);//name=园丁,age=45,salary=4600.0}//定义一个方法public void showInfo(Person p){//打印出对应的name和ageSystem.out.print("name="+p.name+",age="+p.age);if(p instanceof Student){Student s=(Student)p;System.out.println(",no="+s.no);}else if(p instanceof Teacher){Teacher t=(Teacher)p;System.out.println(",salary="+t.salary);}}}//定义一个Person类class Person {public String name;public int age;Person(String name,int age){this.name=name;this.age=age;}}//定义一个学生类class Student extends Person {public int no;Student(String name,int age,int no){super(name,age);this.no=no;}}//定义一个教师类class Teacher extends Person {public double salary;Teacher(String name,int age,double salary){super(name,age);this.salary=salary;}}