[英]How to use string to compare with field names in java?
I have a class named MyClass. 我有一个名为MyClass的类。 It has many fields of type MyField.
它具有MyField类型的许多字段。 How do I return a reference to a particular field whose name matches a String's value?
如何返回对名称与字符串值匹配的特定字段的引用?
public class MyClass{
public MyField field1;
public MyField field2;
public MyField field3;
public MyField whichField(String nameOfField){
//e.g. String = "field3", then return field3
//of course I can do if else, but it will be tedious If I have long list of MyField fields, can I iterate over all field names, and return whose name matches?
}
}
I tried reflection from the answers below, I create a temp placeholder, and I wish to reutrn it but, 我尝试从下面的答案中进行反思,我创建了一个临时占位符,但我希望保留它,但是,
MyField temp = MyClass.class.getDeclaredField(whichFieldString);
doesnt work, I get type mismatch, cant convert error 不起作用,我得到类型不匹配,无法转换错误
How do I cast this? 我该如何投放? How do I return this field?
如何返回此字段?
As an alternative: 作为备选:
If all fields are of the same type and are accessed by their field name (most of the time) you could avoid the hassle and brittleness of using reflection by utilizing a Map
. 如果所有字段都属于同一类型并且可以通过它们的字段名称(大多数情况下)进行访问,则可以通过使用
Map
来避免使用反射的麻烦和脆弱性。
The map associates a key (in your case the "field name") with a value. 该映射将一个键(在您的情况下为“字段名称”)与一个值相关联。 Instead of an arbitrary number of fields, MyClass would look like:
代替任意数量的字段,MyClass看起来像:
public class MyClass {
private final Map<String, MyField> fields = new HashMap<>();
/* code to initially fill the map */
public MyField whichField(String fieldName) {
return fields.get(fieldName);
}
}
You can do it easily with reflection 您可以轻松完成反射
Class<MyClass> clazz = MyClass.class;
Field requieredField = clazz.getDeclaredField("myFielldName");
EDIT 编辑
This solution is pertinent is the number of fields is fixed. 与该解决方案有关的是字段数是固定的。 As it was mentioned in comments and answers, if you want to store a dynamic number of values, then a Map (or a Collection if you only need to enumerate the values) is much more suitable.
正如注释和答案中提到的那样,如果要存储动态数量的值,则Map(或者Collection,如果只需要枚举值)则更合适。
You can do this with reflection. 您可以通过反射来做到这一点。 Class A has the fields we want to search through:
A类具有我们要搜索的字段:
public class A {
private String field1;
private String field2;
private String field3;
}
And B shows how to iterate over the fields declared in A, matching on a particular field name: B显示了如何遍历A中声明的字段,并与特定的字段名称匹配:
public class B {
public B() {
Field field = findFieldByName("field1");
System.out.println(field);
}
private Field findFieldByName(String name) {
Field[] fields = A.class.getDeclaredFields();
for(Field f : fields) {
if(f.getName().equals(name)) {
return f;
}
}
return null;
}
public static void main(String[] args) {
new B();
}
}
You'll have to use reflection: 您必须使用反射:
import java.lang.reflect.Field;
public class MyClass {
public MyField field1;
public MyField field2;
public MyField field3;
public MyField whichField(String nameOfField) {
MyField fieldName = null;
Field[] fields = MyClass.class.getDeclaredFields();
for (Field field : fields) {
if (field.getName().equals(nameOfField)) {
// Do whatever you want to do
}
}
return null;
}
}
class MyField {
}
您可能要使用一个集合,例如Map<String, MyField>
。
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