关于java重写中的方法

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()");
    }
}

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);
    }
}

这是子类

RoundGlyph

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

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);
    }
}

我们使用这个类来测试

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

super（）

时在类

RoundGlyph

中执行方法

draw（）

和打印

RoundGlyph.draw(), radius = 0

---

这是一个多态性！当您从父级调用方法时，如果存在重写，则子级中的方法将被调用。如果要调用parent的方法，必须执行以下操作：

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);
 }
}

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()");
 }
}

或者您必须在父级中进行显式方法调用，如下所示：

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);
 }
}

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()");
 }
}

---

阅读多态性和重写方法。在任何情况下，正如您的代码所示，这也是您不应该从构造函数调用实例方法的原因。