java使用私有构造函数访问私有内部类的重写方法

Question

请查找以下代码段： 等级规则

public class Rules {

    public static final JarvisFilterRule FILTER = new JarvisFilterRule();

    private static class JarvisFilterRule extends RelOptRule {
        private JarvisFilterRule() {
            super(operand(Filter.class, operand(Query.class, none())));
        }

        public void onMatch(RelOptRuleCall call) {
        // do something
        }
    }
}

类重新编译

public abstract class RelOptRule {

  /**
   * Description of rule, must be unique within planner. Default is the name
   * of the class sans package name, but derived classes are encouraged to
   * override.
   */
    protected final String description;
    public abstract void onMatch(RelOptRuleCall call);
}

我的问题是：如何访问嵌套类规则的onMatch（）方法。JarvisFilterRule

Answer 1

Rules.FILTER.onMatch(...)

JarvisFilterRule不是内部类。Java中的内部类是非静态的嵌套类

Answer 2

private关键字的目的是防止访问需要由声明它的类独占使用的类成员

在您的例子中，Rules类将JarvisFilterRule定义为一个private内部类，其实现应该只为Rules类所知

如果希望访问另一个类中的JarvisFilterRule::onMatch()方法，则需要将JarvisFilterRule的private修饰符替换为public，或者将内部类JarvisFilterRule移动到其自己的单独文件中，并使其成为public类。像这样：

JarvisFilterRule .java

public class JarvisFilterRule extends RelOptRule {
        public JarvisFilterRule() {
            super(operand(Filter.class, operand(Query.class, none())));
        }

        public void onMatch(RelOptRuleCall call) {
        // do something
        }
    }

或

public class Rules {

    public static final JarvisFilterRule FILTER = new JarvisFilterRule();

    public static class JarvisFilterRule extends RelOptRule {
        private JarvisFilterRule() {
            super(operand(Filter.class, operand(Query.class, none())));
        }

        public void onMatch(RelOptRuleCall call) {
        // do something
        }
    }
}

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希望这有帮助