java - 确定通用类型字段的类类型

Question

我收到以下代码的NoSuchFieldException:

public class MultipleSorting<T> extends Observable {
    private SelectItem[] criteria1;
    private SelectItem[] order1;
    private SelectItem[] criteria2;
    private SelectItem[] order2;
    private SelectItem[] criteria3;
    private SelectItem[] order3;

    private T criteriaType;

    private T selectedCriteria1;
    private SortOrder selectedOrder1;
    private T selectedCriteria2;
    private SortOrder selectedOrder2;
    private T selectedCriteria3;
    private SortOrder selectedOrder3;    

    private Boolean[] enabledRows = new Boolean[]{Boolean.TRUE, Boolean.FALSE, Boolean.FALSE};

    private Boolean addButtonVisible1 = Boolean.TRUE;
    private Boolean addButtonVisible2 = Boolean.FALSE;
    private Boolean addButtonVisible3 = Boolean.FALSE;

    public MultipleSorting() {
        super();
    }

    private Class<T> getCriteriaClass() throws NoSuchFieldException {
        Field field = this.getClass().getField("criteriaType");
        field.setAccessible(true);
        return (Class<T>)field.getType();
    }

    public void addOrRemoveRow(ActionEvent event) {
        // other codes
        Method setSelectedCriteriaMethod = getClass().getDeclaredMethod("setSelectedCriteria" + (index + 1), new Class[]{getCriteriaClass()});  
        // other codes
    }

    // getters and setters
}

当我调用方法 getCriteriaClass() 时，出现异常。 criteriaType 没有任何 getter 和 seeter 方法。该字段也未初始化。这就是为什么我无法调用 criteriaType.getClass()，因为它抛出 NullPointerException。

我的目标是确定 T 的类类型，并且我不想在此 MultipleSorting 类的构造函数中传递 T 的类。

我无法理解为什么会收到 NoSuchFieldException。任何指针都会对我非常有帮助。

Answer 1

如果你看JavaDoc of getField() ，你看到问题了:

Returns a Field object that reflects the specified public member field of the class or interface represented by this Class object.

您需要使用:

Field field = this.getClass().getDeclaredField("criteriaType");

来自JavaDoc ofgetDeclaredField() :

Returns a Field object that reflects the specified declared field of the class or interface represented by this Class object.

请注意，与 getField() 不同，getDeclaredField() 不会查找继承的字段。