[英]Determine class type of Generic typed field
I am getting NoSuchFieldException
for the following piece of code: 我正在为下面的代码获取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
}
I am getting the exception when I invoke the method getCriteriaClass()
. 调用方法getCriteriaClass()
时遇到异常。 The criteriaType
doesn't have any getter and seeter method. criteriaType
没有任何吸气剂和吸气剂方法。 Also this field is not initialized. 同样,该字段未初始化。 That is why I cannot call criteriaType.getClass()
as it is throwing NullPointerException
. 这就是为什么我无法调用criteriaType.getClass()
因为它引发了NullPointerException
。
My aim is to determine the class type of T
and I don't want to pass the class of T in the constructor of this MultipleSorting
class. 我的目的是确定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。
I am unable to understand why I am getting NoSuchFieldException
. 我不明白为什么我得到NoSuchFieldException
。 Any pointer would be very helpful to me. 任何指针对我都会非常有帮助。
If you look at the JavaDoc of getField()
, you see the problem: 如果查看getField()
的JavaDoc ,则会看到问题:
Returns a Field object that reflects the specified public member field of the class or interface represented by this Class object. 返回一个Field对象,该对象反映此Class对象表示的类或接口的指定公共成员字段 。
You need to use: 您需要使用:
Field field = this.getClass().getDeclaredField("criteriaType");
From the JavaDoc of getDeclaredField()
: 从getDeclaredField()
的JavaDoc中 :
Returns a Field object that reflects the specified declared field of the class or interface represented by this Class object. 返回一个Field对象,该对象反映此Class对象表示的类或接口的指定声明字段。
Note that getDeclaredField()
, unlike getField()
, won't find inherited fields. 请注意,与getField()
不同, getDeclaredField()
不会找到继承的字段。
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