Question

这是超类：Glyph

public class Glyph {
    void draw() {
        System.out.println("Glyph.draw(");
    }
    Glyph() {
        System.out.println("Glyph() before draw()");
        draw();
        System.out.println("Glyph() after draw()");
    }
}

这是子类RoundGlyph

class RoundGlyph extends Glyph {
    int radius = 1;
    RoundGlyph(int r) {
        super();
        radius = r;
        System.out.println("RoundGlyph.RoundGlyph(), radius = " + radius);
    }

    void draw() {
        System.out.println("RoundGlyph.draw(), radius = " + radius);
    }
}

我们使用这个类进行测试。

public class PolyConstructors {
    public static void main(String[] args) {
        new RoundGlyph(5);
    }
}

输出：

Glyph() before draw()
 RoundGlyph.draw(), radius = 0
 Glyph() after draw()
 RoundGlyph.RoundGlyph(), radius = 5

为什么程序在执行draw()时会在类RoundGlyph中执行方法super()？

并打印

RoundGlyph.draw(), radius = 0

Answer 1

它是一种多态性！当您从父方法调用方法时，如果存在覆盖，则子方法将调用。如果你想调用父方法，你必须这样做：

class RoundGlyph extends Glyph {
   int radius = 1;
   RoundGlyph(int r) {
    super();
    radius = r;
    System.out.println("RoundGlyph.RoundGlyph(), radius = " + radius);
  }
@Override
void draw() {
   super.draw();//go draw in parent first
   System.out.println("RoundGlyph.draw(), radius = " + radius);
 }
}

或者您必须在父母中进行显式方法调用，如下所示：

public class Glyph {
 void draw() {
  System.out.println("Glyph.draw(");
 }
 Glyph() {
  System.out.println("Glyph() before draw()");
  Glyph.draw();//explicit calling
  System.out.println("Glyph() after draw()");
 }
}

关于java重写的方法

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