java - 重写 Java 中的构造函数

Question

在学校，我需要学习 Java，而且由于我习惯了基于 C++(如 Cocoa/Objective-C)的语言，所以我对 Java 感到非常沮丧。

我创建了一个父类(super class)(也可以用作基类):

public class CellView {
    public CellViewHelper helper; // CellViewHelper is just an example

    public CellView() {
        this.helper = new CellViewHelper();
        this.helper.someVariable = <anything>;

        System.out.println("CellView_constructor");
    }
    
    public void draw() {
        System.out.println("CellView_draw");
    }

    public void needsRedraw() {
        this.draw();
    }

}

public class ImageCellView extends CellView {

    public Image someImage;

    public ImageCellView() {
        super();
        this.someImage = new Image();
        System.out.println("ImageCellView_constructor");
    }

    public void setSomeParam() {
        this.needsRedraw(); // cannot be replaced by this.draw(); since it's some more complicated.
    }

    @Override public void draw() {
        super.draw();
        System.out.println("ImageCellView_draw");
    }

}

现在，当我这样调用它时:

ImageCellView imageCellView = new ImageCellView();
imageCellView.setSomeParam();

我明白了:

CellView_constructor

ImageCellView_constructor

CellView_draw

但是，我希望它是:

CellView_constructor

ImageCellView_constructor

CellView_draw

ImageCellView_draw

我该怎么做？

提前致谢，

蒂姆

编辑:

我也在CellView中实现了这个方法:

public void needsRedraw() {
    this.draw();
}

这对于 ImageCellView 来说:

public void setSomeParam() {
    this.needsRedraw(); // cannot be replaced by this.draw(); since it's some more complicated.
}

我一直这样称呼:

ImageCellView imageCellView = new ImageCellView();
imageCellView.setSomeParam();

这是否会导致问题(当我从 super 调用函数时，它仅调用 super )？我怎样才能解决这个问题...(不必在每个子类中重新定义/覆盖 needRedraw() 方法？)

Answer 1

您应该得到正确的输出。

我试过你的例子只是评论了不相关的事情:

import java.awt.Image;

public class CellView {
    //public CellViewHelper helper; // CellViewHelper is just an example

    public CellView() {
        //this.helper = new CellViewHelper();
        //this.helper.someVariable = <anything>;

        System.out.println("CellView_constructor");
    }

    public void draw() {
        System.out.println("CellView_draw");
    }

    public static void main(String[] args) {
        ImageCellView imageCellView = new ImageCellView();
        imageCellView.draw();
    }
}

class ImageCellView extends CellView {

    public Image someImage;

    public ImageCellView() {
        super();
        //this.someImage = new Image();
        System.out.println("ImageCellView_constructor");
    }

    @Override public void draw() {
        super.draw();
        System.out.println("ImageCellView_draw");
    }

}

我得到以下输出:

CellView_constructor

ImageCellView_constructor

CellView_draw

ImageCellView_draw

这正是您想要的，这就是您的代码打印的内容。