为什么外部Java类可以访问内部类私有成员？

public class Outer {
    private int value = 10;

    public class Inner {
        public void printValue() {
            System.out.println(value);
        }
    }
}

public class Outer {
    private int value = 10;

    public class Inner {
        public void printValue() {
            System.out.println(value);
        }
    }

    public void printValue() throws Exception {
        Inner inner = new Inner();
        Field field = Inner.class.getDeclaredField("value");
        field.setAccessible(true);
        System.out.println(field.getInt(inner));
    }
}