有没有办法从超类访问子类元素？

Question

我需要一个将在子类中使用的类中的方法，尽管此方法使用在子类中更改的属性。有没有一种方法可以访问子类的属性而不必重写方法？

我试过为该属性使用吸气剂，但得到了相同的结果。

public class SuperClass {

    private static final String a = "Super";

    public void superMethod(){

        System.out.println("SuperMethod: " + a);

    }

}

public class ChildClass extends SuperClass {

    private static final String a = "Child";

}

public class Main {

    public static void main(String[] args) {

        SuperClass s = new SuperClass();

        ChildClass c = new ChildClass();

        s.superMethod();

        c.superMethod();

    }

}

控制台显示：

超级方法：超级

超级方法：超级

预期结果是：

超级方法：超级

超级方法：孩子

Answer 1

我试过为该属性使用吸气剂，但得到了相同的结果。你确定吗？以下应该正是您所追求的：class SuperClass {    private String a = "Super";    public void superMethod() {        System.out.println("SuperMethod: " + getA());    }    public String getA() {        return this.a;    }}class ChildClass extends SuperClass {    private String a = "Child";    @Override    public String getA() {        return this.a;    }}public class Main {    public static void main(String[] args) {        SuperClass s = new SuperClass();        ChildClass c = new ChildClass();        s.superMethod();        c.superMethod();    }}请注意，getter 不能是私有的（否则无法从类外部访问它们），并且它们不能是静态的（否则它们是类的一部分，而不是该类的任何实例。）

Answer 2

目前尚不清楚你在做什么，但你的String a成员是private static班级的成员，而不是个别对象的成员。如果您创建了String a对象的成员，而不是类的成员，则可以在创建子类期间覆盖该值：U:\>jshell|  Welcome to JShell -- Version 12|  For an introduction type: /help introjshell> class SuperClass {   ...>    protected final String a;   ...>   ...>    protected SuperClass(String _a) {   ...>       a = _a;   ...>    }   ...>   ...>    public SuperClass() {   ...>       this("Super");   ...>    }   ...>   ...>    public void superMethod() {   ...>       System.out.println("SuperMethod: "+a);   ...>    }   ...> }|  created class SuperClassjshell> class ChildClass extends SuperClass {   ...>    public ChildClass() {   ...>      super("Child");   ...>    }   ...> }|  created class ChildClassjshell> var s = new SuperClass();s ==> SuperClass@4566e5bdjshell> var c = new ChildClass();c ==> ChildClass@ff5b51fjshell> s.superMethod();SuperMethod: Superjshell> c.superMethod();SuperMethod: Child更新现在我们知道了您的实际用例（来自下面的评论），您想要实现的内容非常简单：class SuperClass {    private final static Logger LOG = Logger.getLogger(SuperClass.class);    protected Logger getLogger() { return LOG; }    public void superMethod(){        getLogger().info("superMethod() called.");    }}class ChildClass extends SuperClass {    private final static Logger LOG = Logger.getLogger(ChildClass.class);    @Override    protected Logger getLogger() { return LOG; }}public class Main {    public static void main(String[] args) {        SuperClass s = new SuperClass();        ChildClass c = new ChildClass();        s.superMethod();                 // Message logged to SuperClass.LOG        c.superMethod();                 // Message logged to ChildClass.LOG    }}

Answer 3

简短回答：Java 无法按照您想要的方式执行此操作，因为编译器会将 String 文字与最终值合并，因此"SuperMethod: " + a将在生成的字节码中进行转换"SuperMethod: Super"。唯一的解决方案是使用反射（如果必须的话）：import java.lang.reflect.Field;public class Main {&nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; SuperClass s = new SuperClass();&nbsp; &nbsp; &nbsp; ChildClass c = new ChildClass();&nbsp; &nbsp; &nbsp; s.superMethod();&nbsp; &nbsp; &nbsp; c.superMethod();&nbsp; }}class SuperClass {&nbsp; &nbsp; private static final String a = "Super";&nbsp; &nbsp; public void superMethod(){&nbsp; &nbsp; &nbsp; try{&nbsp; &nbsp; &nbsp; &nbsp; final Class<?> clazz = this.getClass();&nbsp; &nbsp; &nbsp; &nbsp; final Field fieldA = clazz.getDeclaredField("a");&nbsp; &nbsp; &nbsp; &nbsp; fieldA.setAccessible(true);&nbsp; &nbsp; &nbsp; &nbsp; final String value = (String)fieldA.get(null);&nbsp; &nbsp; &nbsp; &nbsp; System.out.println("SuperMethod: " + value);&nbsp; &nbsp; &nbsp; } catch (final NoSuchFieldException | IllegalAccessException ex){&nbsp; &nbsp; &nbsp; &nbsp; // Because reflection&nbsp; &nbsp; &nbsp; &nbsp; ex.printStackTrace();&nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}class ChildClass extends SuperClass {&nbsp; &nbsp; private static final String a = "Child";}输出是：SuperMethod: SuperSuperMethod: Child但是，老实说，我仍然喜欢使用经典覆盖：public class Main {&nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; SuperClass s = new SuperClass();&nbsp; &nbsp; &nbsp; ChildClass c = new ChildClass();&nbsp; &nbsp; &nbsp; s.superMethod();&nbsp; &nbsp; &nbsp; c.superMethod();&nbsp; }}class SuperClass {&nbsp; &nbsp; private static final String a = "Super";&nbsp; &nbsp; public void superMethod(){&nbsp; &nbsp; &nbsp; &nbsp; System.out.println("SuperMethod: " + getA());&nbsp; &nbsp; }&nbsp; &nbsp; public String getA() {&nbsp; &nbsp; &nbsp; return a;&nbsp; &nbsp; }}class ChildClass extends SuperClass {&nbsp; &nbsp; private static final String a = "Child";&nbsp; &nbsp; @Override&nbsp; &nbsp; public String getA() {&nbsp; &nbsp; &nbsp; return a;&nbsp; &nbsp; }}