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如雨随形space

#1 Created at ... [Delete] [Delete and Lock User]

如果把Person的hello设为private的那么打印出来的是Person:hello，怎么解释呢？

廖雪峰

#2 Created at ... [Delete] [Delete and Lock User]

Exception in thread "main" java.lang.NoSuchMethodException: Person.hello()

编译不过的情况下，你运行的是旧的class

如雨随形space

#3 Created at ... [Delete] [Delete and Lock User]

您运行一下这段代码，我的环境jdk1.8.0_181能通过编译

public class Main {    public static void main(String[] args) throws Exception{        MyPerson std = new MyStudent();        Method m = MyPerson.class.getDeclaredMethod("sayHello");        m.setAccessible(true);        m.invoke(std);    }}class MyPerson {    private void sayHello() {        System.out.println("Person:hello");    }}class MyStudent extends MyPerson {    public void sayHello() {        System.out.println("Student:hello");    }}

如雨随形space

#4 Created at ... [Delete] [Delete and Lock User]

public class Main {
    public static void main(String[] args) throws Exception{
        MyPerson std = new MyStudent();        Method m = MyPerson.class.getDeclaredMethod("sayHello");        m.setAccessible(true);        m.invoke(std);    }
}

class MyPerson {
    private void sayHello() {
        System.out.println("Person:hello");    }
}

class MyStudent extends MyPerson {
    public void sayHello() {
        System.out.println("Student:hello");    }
}