类对象的 显示转换 和 隐式转换

类对象的 显示转换 和 隐式转换

public class Employee {
    int a = 1 ;
	public  void work(){} ;
    public  void getPay(){} ;
}



public class Teacher extends Employee{
    int a = 1000 ;
	@Override
	public void getPay() {
		System.out.println("发工资了！！") ;
	}

	@Override
	public void work() {
		System.out.println("又要上班了！！") ;
	}

	public void driveCar(){
		System.out.println("开车旅游去了！！") ;
	}
}

一、隐式转换（子类 --> 父类）

Employee emp = new Teacher() ;

System.out.println(emp instanceof Employee) ;//true

System.out.println(emp instanceof Teacher) ; //true
注意此处，虽然emp也是Teacher的实例对象，但emp只能调用Employee类里面有的属性和方法，不能调用Teacher类自己新定义的属性或方法。

二、显示转换（强制转换）（父类 --> 子类）

Employee emp = new Teacher() ;
Teacher empTotea = (Teacher)emp ; //父类 --> 子类

System.out.println(empTotea instanceof Employee) ;//true
System.out.println(empTotea instanceof Teacher) ; //true

Employee e = new Employee() ;
Teacher t2 = (Teacher)e ;       //父类 --> 子类

编译可以通过，但运行时会报错：ClassCastException
Exception in thread "main" java.lang.ClassCastException: com.org.momo.instanseof.Employee cannot be cast to com.org.momo.instanseof.Teacher
	at com.org.momo.instanseof.Test.main(Test.java:7)