无法从抽象类中调用非静态方法

Question

我正在尝试从SingleChoiceViewHolder.java中的SettingsItem.java调用getSetting() 。 有没有一种方法可以在保持SettingsItem为非静态抽象类的同时调用getSetting() ？ 这是我尝试添加到SingleChoiceViewHolder.java中的内容，但是Android Studio表示“ SettingsItem”是抽象的； 无法实例化：

 SettingsItem instance = new SettingsItem(); instance.getSetting(); IntSetting setting = (IntSetting) getSetting(); mTextSettingDescription.setText(setting.getValue()); 

我也尝试过将SettingsItem转换为接口，并与SingleChoiceViewHolder extends SettingViewHolder实现它SingleChoiceViewHolder extends SettingViewHolder但原始问题仍然存在。

这些文件附在下面。

SingleChoiceViewHolder.java：

 public final class SingleChoiceViewHolder extends SettingViewHolder { private SingleChoiceSetting mItem; private TextView mTextSettingName; private TextView mTextSettingDescription; public SingleChoiceViewHolder(View itemView, SettingsAdapter adapter) { super(itemView, adapter); } @Override protected void findViews(View root) { mTextSettingName = (TextView) root.findViewById(R.id.text_setting_name); mTextSettingDescription = (TextView) root.findViewById(R.id.text_setting_description); } @Override public void bind(SettingsItem item) { mItem = (SingleChoiceSetting) item; mTextSettingName.setText(item.getNameId()); if (item.getDescriptionId() == R.string.dynamic_descriptionId) { SettingsItem instance = new SettingsItem(); instance.getSetting(); IntSetting setting = (IntSetting) getSetting(); mTextSettingDescription.setText(setting.getValue()); } if (item.getDescriptionId() > 0 && item.getDescriptionId() != R.string.dynamic_descriptionId) { mTextSettingDescription.setText(item.getDescriptionId()); } } @Override public void onClick(View clicked) { getAdapter().onSingleChoiceClick(mItem); } 

SettingsItem.java：

 public abstract class SettingsItem { public static final int TYPE_HEADER = 0; public static final int TYPE_CHECKBOX = 1; public static final int TYPE_SINGLE_CHOICE = 2; public static final int TYPE_SLIDER = 3; public static final int TYPE_SUBMENU = 4; public static final int TYPE_INPUT_BINDING = 5; public static final int TYPE_RADIO_BUTTON = 6; private String mKey; private String mSection; private int mFile; private Setting mSetting; private int mNameId; private int mDescriptionId; public SettingsItem(String key, String section, int file, Setting setting, int nameId, int descriptionId) { mKey = key; mSection = section; mFile = file; mSetting = setting; mNameId = nameId; mDescriptionId = descriptionId; } public String getKey() { return mKey; } public String getSection() { return mSection; } public int getFile() { return mFile; } public Setting getSetting() { return mSetting; } public void setSetting(Setting setting) { mSetting = setting; } public int getNameId() { return mNameId; } public int getDescriptionId() { return mDescriptionId; } public abstract int getType(); } 

Answer 1

按照定义，抽象类意味着它没有实例化，但是您可以从中继承。 如果要创建许多具有相同值但名称不同的对象，则可以扩展SettingsItem。

另外，如果您希望更多抽象以供将来使用，则可以使用与抽象方法相同的方法来创建接口，以防需要为其他设置项创建自定义方法。

例：

interface SettingsInterface {
    void doSomething();
}

class abstract SettingsItem implements SettingsInterface {
    public void doSomething() {
        System.out.println("Hello");
    }
}

class RegularSettings extends SettingsItem {}

class CustomSettings implements SettingsInterface {
    public void doSomething() {
        System.out.println("Goodbye");
    }
}

class TestClass {

    public static void testAbstract(SettingsItem extendedAbstract) {
        extendedAbstract.doSomething();
    }

    public static void testInterface(SettingsInterface interface) {
        interface.doSomething();
    }

    public static void main(String[] args) {
        SettingsItem abstractExtended = new RegularSettings();
        // also could be CustomSettings instead of SettingsInterface
        SettingsInterface customClass = new CustomSettings();

        testInterface(abstractExtended);
        testInterface(customClass);

        testAbstract(abstractExtended);
        // will throw errors since it doesn't extend SettingsItem
        testAbstract(customClass);
    }
}

Answer 2

由于getSetting（）不是静态方法，因此您需要在扩展抽象类SettingsItem的某些具体类的实例上调用它。

想一想。 如果您有一个此类的两个实例，并且两个实例的mSetting变量不同，则应该从对getSetting（）的类似静态的调用中返回哪个实例？