如何在子类中设置实例变量，即使它是私有的并在超类中声明？

Question

import javax.swing.ImageIcon;

public class City {
private String name;
private int population, x, y;
private ImageIcon marker;

public City(String name, int population, int x, int y) {
    marker = new ImageIcon("marker_city.png");
    this.name = name;
    this.population = population;
    this.x = x;
    this.y = y;
}

public ImageIcon getMarker() {
    return marker;
}

public void setMarker(ImageIcon marker) {
    this.marker = marker;
}

public String toString() {
    return this.name;
}
}

我需要用不同的 ImageIcon 文件创建一个子类 ("marker_prov.png")。我应该如何设置 marker 变量？这个必须在超类中保持私有。

import javax.swing.ImageIcon;

public class ProvCapital extends City {
private String province;

public ProvCapital(String name, int population, int x, int y, String province) {
    super(name, population, x, y, marker);
    marker = new ImageIcon("marker_prov.png");
    this.province = province;
}

我想我可以使用 getter 或 setter，因为它们是 public，但我不知道如何使用。

Answer 1


marker = new ImageIcon("marker_prov.png");
setMarker(marker);

应该这样做吗？

Answer 2

我建议更改 class ProvCapital 的构造函数。删除 marker 参数，因为无论如何您都会忽略它。试试下面的构造函数。

public ProvCapital(String name, int population, int x, int y, String province) {
    super(name, population, x, y, new ImageIcon("marker_prov.png"));
    this.province = province;
}

编辑

实际上，我看到您在 class City 的构造函数中也忽略了 marker 参数，所以最好也放弃它。只保留 setMarker() 方法。为 class City

尝试以下构造函数

public City(String name, int population, int x, int y) {
    setMarker(new ImageIcon("marker_city.png"));
    this.name = name;
    this.population = population;
    this.x = x;
    this.y = y;
}

然后如下更改 class ProvCapital 的构造函数。

public ProvCapital(String name, int population, int x, int y, String province) {
    super(name, population, x, y);
    setMarker(new ImageIcon("marker_prov.png"));
    this.province = province;
}

Answer 3

在 City 中添加一个新的（受保护的）构造函数，它将 marker 作为参数：

protected City(String name, int population, int x, int y, ImageIcon marker) {
    this.name = name;
    this.population = population;
    this.x = x;
    this.y = y;
    this.marker = marker;
}

理想情况下，在 public 构造函数中重用它：

public City(String name, int population, int x, int y) {
    this(name, popoulation, x, y, new ImageIcon("marker_city.png"));
}

然后在子类的 super() 调用中传递选定的标记：

public ProvCapital(String name, int population, int x, int y, String province) {
    super(name, population, x, y, new ImageIcon("marker_prov.png"));
    this.province = province;
}

如果需要，这种方法甚至允许您删除 setter 并使 marker 最终化。

如何在子类中设置实例变量，即使它是私有的并在超类中声明？

How to set an instance variable in subclass even though it's private and declared in superclass?

java

subclass

superclass

imageicon

编辑