java - 我认为内部类可以访问外部类变量/方法？

Question

我确实阅读了许多讨论内部类的主题，我的印象是内部类可以访问封闭类的变量和方法。下面我有一个外部类和一​​个内部类，在测试类中我创建了一个外部类的实例，然后从中创建了一个内部类的实例。但是我无法通过内部类引用访问 String 变量 a。帮助？

public class OuterClass {

    String a = "A";
    String b = "B";
    String c = "C";

    class InnerClass {
        int x;

    }

    public static class StaticInnerClass {
        int x;
    }

    public String stringConCat() {
        return a + b + c;

    }
}

public class TestStatic {

    public static void main(String args[]) {

        OuterClass.StaticInnerClass staticClass = new OuterClass.StaticInnerClass();
        OuterClass outer = new OuterClass();
        OuterClass.InnerClass inner = outer.new InnerClass();

        System.out.println(inner.a);// error here, why can't i access the string
                                    // variable a here?

    }
}

Answer 1

内部类可以通过自己的方法访问外部类的方法和属性。看下面的代码:

class OuterClass {

    String a = "A";
    String b = "B";
    String c = "C";

    class InnerClass{
        int x;
        public String getA(){
            return a; // access the variable a from outer class
        }
    }

    public static class StaticInnerClass{
        int x;
    }

    public String stringConCat(){
        return a + b + c;    
    }
}


public class Test{

    public static void main(String args[]) {

        OuterClass.StaticInnerClass staticClass = new OuterClass.StaticInnerClass();
        OuterClass outer = new OuterClass();
        OuterClass.InnerClass inner = outer.new InnerClass();

        System.out.println(inner.getA()); // This will print "A"
    }
}