blocks|key|5502299|text|因为这两个类(A和B)都嵌套在Main中，所以它们可以访问private+int+f()方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5502300|如果您在顶级类中提取A和B的源代码，这种情况就不会发生，并且您将无法编译。|5502301|entityMap^0|7|1|9|1|F|4|T|F|0|A|1|C|1|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|I|$]]

Since both of the classes (<code>A</code> and <code>B</code>) are nested in <code>Main</code>, they can access the <code>private int f()</code> method.

If you extract the sources of <code>A</code> and <code>B</code> in top-level classes, this won't happen and you'll fail to compile.

blocks|key|1381154|text|private的要点是“外部”类不应该能够看到私有变量。但是A和B都是同一个类的一部分，或者彼此嵌套在一起，所以它们可以访问彼此的私有成员。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1381155|所以这将会起作用：|1381156|public+class+A+{

+++private+void+a()+{
+++++int+bVal+=+this.new+B().val;+++//!+Accessing+B+private
+++}

+++class+B+{
++++++A+a+=+new+A();
++++++private+int+val+=+10;
++++++public+void+b()+{
+++++++++a.a();++++++//+!!+Accessing+A+private
++++++}
}|code-block|syntax|javascript|1381157|但是，即使A和B都在相同的文件中，但不在彼此内部，这也会失败：|offset|length|style|BOLD|1381158|class+A+{
++++private+void+a()+{}
}

class+B+extends+A+{
+++A+a+=+new+A();
+++public+void+b()+{
++++++a.a();++//+can't+see+even+if+B+extends+A
+++}
}|1381159|entityMap^0|0|0|0|D|2|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@$K|W|L|X|M|N]]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

The point of private is that "outside" classes should not be able to see private variables. But A and B are both part of the same class, or are nested within each other, so they can access each others private members. 

So this will work:

<pre><code>public class A {

 private void a() {
 int bVal = this.new B().val; //! Accessing B private
 }

 class B {
 A a = new A();
 private int val = 10;
 public void b() {
 a.a(); // !! Accessing A private
 }
}
</code></pre>

BUT, this will fail, even if both A and B are in the same file but not within each other:

<pre><code>class A {
 private void a() {}
}

class B extends A {
 A a = new A();
 public void b() {
 a.a(); // can't see even if B extends A
 }
}
</code></pre>

blocks|key|5367067|text|这是因为A类和B类都嵌套在另一个类中，也就是说，这两个类都是另一个相同类的内部类(或“部分”)。因为它们(数据成员和方法)基本上是外部类的成员，所以即使是私有的，它们也可以在其他内部类中访问。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5367068|Java允许我们嵌套类，如果您不了解嵌套类，请先阅读以下内容：|5367069|http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html|offset|length|5367070|class+Outer{


class+A+{
++++private+int+f()+{
++++++++return+42;
++++}//Method+f()+is+a+private+member+of+A+and+accessible+by+Outer
}

class+B+extends+A+{
++++public+int+f2()+{
++++++++return+super.f();+
++++}//As+class+B+is+inner+class+of+Outer+it+can+access+members+of+outer,thus+indirectly+member+of+A+
}

public+static+void+main(String[]+args)+{
++++System.out.print(new+B().f2());

}

}|code-block|syntax|javascript|5367071|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|1Q|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@$F|W|G|X|1|Y]]|A|$]]|$1|H|3|I|5|J|7|Z|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|E]]]]

This is because both classes A and B are nested inside another class, i.e both classes are inner classes of (or "part of") another same class. Since they (Data Members and Methods) are basically a member of the outer class,they are accessible within other inner classes even if private. 

Java allows us Nesting of classes,If You Don't know about nested classes first read this : 
<a href="http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html" rel="nofollow">http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html</a>

<pre><code>class Outer{


class A {
 private int f() {
 return 42;
 }//Method f() is a private member of A and accessible by Outer
}

class B extends A {
 public int f2() {
 return super.f(); 
 }//As class B is inner class of Outer it can access members of outer,thus indirectly member of A 
}

public static void main(String[] args) {
 System.out.print(new B().f2());

}

}
</code></pre>

So, one friend sent me this code and said that it had compiled successfully and returned 42.
But, the bothering thing is the method in parent class that "returns" 42 is private, and the method that is called on is in child class, and it's public. So, can anybody tell why and how this works?

<pre><code>static class A {
 private int f() {
 return 42;
 }
}

static class B extends A {
 public int f2() {
 return super.f();
 }
}

public static void main(String[] args) {
 System.out.print(new B().f2());

}
</code></pre>

It returns 42.

I tried to get rid of static, and 

<pre><code>class A {
 private int f() {
 return 42;
 }
}

class B extends A {
 public int f2() {
 return super.f();
 }
}

public static void main(String[] args) {
 Main m= new Main();
 B b= m.new B();
 System.out.print(b.f2());

}
</code></pre>

it still returns 42.

java, inheritance — private field in parent is accessed through a public method in child

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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所以，一个朋友给我发来了这段代码，并说它已经成功编译并返回42。但是，麻烦的是父类中的方法“return”42是私有的，而被调用的方法是在子类中，它是公共的。那么，有没有人能告诉我这是为什么以及如何工作的呢？static class A {    private int f() {        return 42; ...

问java，继承-父级中的私有字段通过子级中的公共方法进行访问
EN

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问java，继承-父级中的私有字段通过子级中的公共方法进行访问EN