关于Java Access Control的4道有趣的测试题_如果没有适当的 access control,naddscoreserviceimpl.java 中-优快云博客

本文链接：https://blog.youkuaiyun.com/smilingleo/article/details/3908756

本文通过四个具体的Java程序案例，深入探讨了不同访问修饰符在继承结构中的表现效果，特别是当子类位于不同包中时，如何正确访问父类的方法。

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好像很简单，测试一下，看你能答对几个？（答案在最后）

问题1

public class p1.C1 { int m() {return 1;} } public class p1.C2 extends C1 { int m() {return 2;} } public class p2.C3 extends p1.C2 { int m() {return 3;} } public class p1.Main { public static void main(String[] args) { C1 c = new p2.C3(); System.out.println(c.m()); } }

Classes C1, C2 and Main are in package p1. C3 is in package p2. What is the output of Main.main()?

a) 1

b) 2

c) 3

问题2

public class p1.C1 { int m() {return 1;} } public class p1.C2 extends C1 { int m() {return 2;} } public class p2.C3 extends p1.C2 { public int m() {return 3;} } public class p1.Main { public static void main(String[] args) { C1 c = new p2.C3(); System.out.println(c.m()); } }

Classes C1, C2 and Main are in package p1. C3 is in package p2. What is the output of Main.main()?

a) 1

b) 2

c) 3

问题3:

public class p1.C1 { int m() {return 1;} } public class p1.C2 extends C1 { protected int m() {return 2;} } public class p2.C3 extends p1.C2 { protected int m() {return 3;} } public class p1.Main { public static void main(String[] args) { C1 c = new p2.C3(); System.out.println(c.m()); } }

Classes C1, C2 and Main are in package p1. C3 is in package p2. What is the output of Main.main()?

a) 1

b) 2

c) 3

问题4

public class p1.C1 { int m() {return 1;} } public class p1.C2 extends C1 { int m() {return 2;} } public class p2.C3 extends p1.C2 { int m() {return 3;} } public class p1.C4 extends p2.C3 { int m() {return 4;} } public class p1.Main { public static void main(String[] args) { C1 c = new p2.C4(); System.out.println(c.m()); } }

Classes C1, C2 and Main are in package p1. C3 is in package p2. What is the output of Main.main()?

a) 1

b) 2

c) 3

d) 4