Java 继承：显式调用构造函数时不能引用实例字段

Question

鉴于我有一个类的层次结构。 父类如下：

public class Utils {

    protected Driver driver;

    public Utils() {
        this.driver = new Driver();
    }

    public Utils(Driver driver,String xPath) {
        this.driver = driver;
        this.driver.waitForElement(xPath, 2);
    }

而孩子是：

public class SelectRegisteredOwner extends Utils {


    final String newOrUsed = "//*[@id=\"root\"]/div/div[3]/div/div[2]/div/div/form/div[3]/div[2]/button[2]";


    public SelectRegisteredOwner( Driver driver) {
        super(driver,newOrUsed);
    }}

问题是，在super(driver,newOrUsed);行中的子类中super(driver,newOrUsed); 它抱怨：

Cannot refer to an instance field newOrUsed while explicitly invoking a constructor

作为快速修复，建议将newOrUsed视为static属性

有没有办法在不使属性静态的情况下解决这个问题？

Answer 1

在类初始化之前，您不能使用最终字段newOrUsed 。 将其设为静态或将其移动到构造函数中。

Answer 2

该字段看起来像一个常量，允许您识别 UI 中的元素。 我会将其设为常量并将其与您的子类分开：

public class Utils {

    private Driver driver;  //make them private and expose getters
    private String xPath;

    public Utils() {
        this.driver = new Driver();
    }

    public Utils(Driver driver,String xPath) {
        this.driver = driver;
        this.xPath = xPath;
        this.driver.waitForElement(xPath, 2);
    }
   protected Driver getDriver(){...}
   protected Driver getXPath(){...}
}

public class SelectRegisteredOwner extends Utils {
    public SelectRegisteredOwner( Driver driver) {
        super(driver,XPathSelector.NEW_OR_USED);
    }
}

public interface XPathSelector{
    String NEW_OR_USED = "//*[@id=\"root\"]/div/div[3]/div/div[2]/div/div/form/div[3]/div[2]/button[2]";
}

Answer 3

由于该字段具有恒定值，因此您可以将其设为static 。 但由于您的要求不是使用static ，我推荐这种方法

class Utils {

    protected Driver driver;

    public Utils() {
        this(new Driver());
    }

    public Utils(Driver driver) {
        this.driver = driver;
    }

    public void addXPath(String xPath) {
        this.driver.waitForElement(xPath, 2);
    }
}

class SelectRegisteredOwner extends Utils {

    final String newOrUsed = "//*[@id=\"root\"]/div/div[3]/div/div[2]/div/div/form/div[3]/div[2]/button[2]";

    public SelectRegisteredOwner(Driver driver) {
        super(driver);
        addXPath(newOrUsed);
    }
}

现在，由于您在Utils有default和overloaded构造函数，这清楚地表明xPath不是强制性的。

因此，一旦构建driver ，您就可以利用常规方法将其添加到driver ，因为添加xPath完全在SelectRegisteredOwner控制范围内。