Cannot reduce the visibility of the inherited method from
2017-01-31 23:04
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source: http://xp9802.iteye.com/blog/2095350
public class Test {
public static void main(String[] args){
People p1=new Student();
System.out.print(p1);
p1.speak();
}
}
abstract class People{
public String sex;
public abstract void speak();
}
class Student extends People{
private String sex;
private void speak(){
System.out.println(" speak Chinese");
}
public String toString(){ //we can override this function both in class People and class Student
return "I";
}
}
运行结果:Cannot reduce the visibility of the inherited method from People
这是因为如果子类要覆盖了父类中定义的方法,那么不能降低其可见性。正如上面的例子,人可以讲话,但学生作为人的一种却不能讲话,这显然是不合理的。即如果在父类中定义一个protected方法,那么在子类中可以将其覆盖,并将访问控制属性改为public,反过来则不行。不过数据域则没有该限制,上例中People类中定义了public String sex;而在子类中定义private String sex;这是可行的,该属性是各自类的成员变量,不存在覆盖的问题。另外,该例中还涉及到了覆盖Object类的toString方法,如果不在子类中重写该方法,那么System.out.print(p1);将会输出类似 speak
Chinese的一个字符串(假设前面所提到的错误已改正),这个字符串的信息不是很有用,应该在子类中加以覆盖,使它返回一个代表该对象的易懂的字符串。覆盖定义的toString()方法既可以写在People类里,也可以写在Student类里,如果两个类中都重写了,最后调用的将是Student类中的toString().
改正了上述错误后,输出结果为:I speak Chinese
public class Test {
public static void main(String[] args){
People p1=new Student();
System.out.print(p1);
p1.speak();
}
}
abstract class People{
public String sex;
public abstract void speak();
}
class Student extends People{
private String sex;
private void speak(){
System.out.println(" speak Chinese");
}
public String toString(){ //we can override this function both in class People and class Student
return "I";
}
}
运行结果:Cannot reduce the visibility of the inherited method from People
这是因为如果子类要覆盖了父类中定义的方法,那么不能降低其可见性。正如上面的例子,人可以讲话,但学生作为人的一种却不能讲话,这显然是不合理的。即如果在父类中定义一个protected方法,那么在子类中可以将其覆盖,并将访问控制属性改为public,反过来则不行。不过数据域则没有该限制,上例中People类中定义了public String sex;而在子类中定义private String sex;这是可行的,该属性是各自类的成员变量,不存在覆盖的问题。另外,该例中还涉及到了覆盖Object类的toString方法,如果不在子类中重写该方法,那么System.out.print(p1);将会输出类似 speak
Chinese的一个字符串(假设前面所提到的错误已改正),这个字符串的信息不是很有用,应该在子类中加以覆盖,使它返回一个代表该对象的易懂的字符串。覆盖定义的toString()方法既可以写在People类里,也可以写在Student类里,如果两个类中都重写了,最后调用的将是Student类中的toString().
改正了上述错误后,输出结果为:I speak Chinese
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