You can use:
String value = (String) this.getClass().getDeclaredField("str").get(this);
Or in a more generalized and safer form:
Field field = anObject.getClass().getDeclaredField(fieldName);
field.setAccessible(true);
String value = (String) field.get(anObject);
And for your example, this should be enough:
String value = this.str;
But you probably know of that one.
Note: anObject.getClass().getDeclaredField() is potentially unsafe as anObject.getClass() will return the actual class of anObject. See this example:
Object anObject = "Some string";
Class<?> clazz = anObject.getClass();
System.out.println(clazz);
Will print:
class java.lang.String
And not:
class java.lang.Object
So for your code's safety (and to avoid nasty errors when your code grows), you should use the actual class of the object you're trying to extract the field from:
Field field = YourObject.class.getDeclaredField(fieldName);
Top answer 1 of 2
13
You can use:
String value = (String) this.getClass().getDeclaredField("str").get(this);
Or in a more generalized and safer form:
Field field = anObject.getClass().getDeclaredField(fieldName);
field.setAccessible(true);
String value = (String) field.get(anObject);
And for your example, this should be enough:
String value = this.str;
But you probably know of that one.
Note: anObject.getClass().getDeclaredField() is potentially unsafe as anObject.getClass() will return the actual class of anObject. See this example:
Object anObject = "Some string";
Class<?> clazz = anObject.getClass();
System.out.println(clazz);
Will print:
class java.lang.String
And not:
class java.lang.Object
So for your code's safety (and to avoid nasty errors when your code grows), you should use the actual class of the object you're trying to extract the field from:
Field field = YourObject.class.getDeclaredField(fieldName);
2 of 2
1
Imagine you have object in variable foo.
Then you need to get Field
Field field = foo.getClass().getDeclaredField("str");
then allow access to private field by:
field.setAccessible(true);
and you can have value by:
Object value = field.get(foo);
Oracle
docs.oracle.com › javase › tutorial › reflect › member › fieldValues.html
Getting and Setting Field Values (The Java™ Tutorials > The Reflection API > Members)
Because such access usually violates the design intentions of the class, it should be used with the utmost discretion. The Book class illustrates how to set the values for long, array, and enum field types. Methods for getting and setting other primitive types are described in Field. import java.lang.reflect.Field; import java.util.Arrays; import static java.lang.System.out; enum Tweedle { DEE, DUM } public class Book { public long chapters = 0; public String[] characters = { "Alice", "White Rabbit" }; public Tweedle twin = Tweedle.DEE; public static void main(String...
java - Reflection generic get field value - Stack Overflow
I am trying to obtain a field's value via reflection. The problem is I don't know the field's type and have to decide it while getting the value. This code results with this exception: Can not set... More on stackoverflow.com
What’s the point of Java reflection?
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3
September 5, 2022Access Java field directly instead of using getter/setter - Language Design - Kotlin Discussions
For example, here is a Java class public class Thing { ... public int thing; public getThing() { return thing; } public setThing(int t) { thing = t; } } In Kotlin, if I want to access thing , I would do the following: val t = Thing() t.thing // get t.thing = 42 //set In the decompiled Kotlin ... More on discuss.kotlinlang.org
1
October 4, 2020(Reflections) Get list of fields?
Did you ask on Stack Overflow ? I know the JetBrains Kotlin team regular post answers there. More on reddit.com
6
4
February 7, 2015Videos
Java Reflection - Get and Set field values
20:07
Java Reflection Explained - bɘniɒlqxƎ noiɟɔɘlʇɘЯ ɒvɒᒐ ...
02:14
How to set and get the field values using java Reflection? | ...
00:47
Accessing Fields of an Interface via Reflection #java #shorts #coding ...
18:26
Java Tutorial - Reflection - Constructor and Method Invocation ...
01:26
How to Access Fields of a Class in Java Using Reflection | Reflection ...
Baeldung
baeldung.com › home › java › core java › retrieve fields from a java class using reflection
Retrieve Fields from a Java Class Using Reflection | Baeldung
January 4, 2026 - Of course, we could use the getDeclaredFields() method on both Person and Employee classes and merge their results into a single array. But what if we don’t want to specify the superclass explicitly?
TutorialsPoint
tutorialspoint.com › javareflect › javareflect_field_get.htm
java.lang.reflect.Field.get() Method Example
The java.lang.reflect.Field.get(Object obj) method returns the value of the field represented by this Field, on the specified object. The value is automatically wrapped in an object if it has a primitive type.
Dev.java
dev.java › learn › reflection › fields
Reading and Writing Fields - Dev.java
A Field object lets you get more information on the corresponding field: its type and its modifiers, and enables you to get the value of this field for a given object, and to set it.
Jenkov
jenkov.com › tutorials › java-reflection › fields.html
Java Reflection - Fields
April 21, 2016 - Class aClass = MyObject.class Field field = aClass.getField("someField"); MyObject objectInstance = new MyObject(); Object value = field.get(objectInstance); field.set(objetInstance, value); The objectInstance parameter passed to the get and ...
Bala's Blog
dkbalachandar.wordpress.com › 2017 › 03 › 08 › how-to-use-reflectionutils-to-retrieve-the-field-value
How to use ReflectionUtils to retrieve the field value | Bala's Blog
March 8, 2017 - import org.apache.commons.lang3.exception.ExceptionUtils; import org.apache.commons.lang3.reflect.FieldUtils; import java.lang.reflect.Field; public class ReflectionUtilsMain { public static void main(String[] args) { Employee employee = new Employee(); employee.setEmpId("1234"); employee.setFirstName("John"); employee.setLastName("Turner"); employee.setDesignation("Manager"); System.out.println(employee); //Now you want to access the First Name from Employee object with Java reflection String firstName = null; String fieldName = "firstName"; for (Class aClass = employee.getClass(); aClass !=
Google Groups
groups.google.com › g › scala-user › c › DT1Ifw8YKvU
how to get value class fields with scala reflection
April 3, 2013 - It looks like that when using runtime reflection, foo becomes the int value (3) because it extends AnyVal. ... This behavior is expected or are we using the reflection API in a wrong way? I get the same result using SMirror: scala> implicit val mirror = scala.reflect.runtime.currentMirror · mirror: reflect.runtime.universe.Mirror = JavaMirror with scala.t...
Top answer 1 of 11
207
You should pass the object to get method of the field, so
import java.lang.reflect.Field;
Field field = object.getClass().getDeclaredField(fieldName);
field.setAccessible(true);
Object value = field.get(object);
2 of 11
189
Like answered before, you should use:
Object value = field.get(objectInstance);
Another way, which is sometimes prefered, is calling the getter dynamically. example code:
public static Object runGetter(Field field, BaseValidationObject o)
{
// MZ: Find the correct method
for (Method method : o.getMethods())
{
if ((method.getName().startsWith("get")) && (method.getName().length() == (field.getName().length() + 3)))
{
if (method.getName().toLowerCase().endsWith(field.getName().toLowerCase()))
{
// MZ: Method found, run it
try
{
return method.invoke(o);
}
catch (IllegalAccessException e)
{
Logger.fatal("Could not determine method: " + method.getName());
}
catch (InvocationTargetException e)
{
Logger.fatal("Could not determine method: " + method.getName());
}
}
}
}
return null;
}
Also be aware that when your class inherits from another class, you need to recursively determine the Field. for instance, to fetch all Fields of a given class;
for (Class<?> c = someClass; c != null; c = c.getSuperclass())
{
Field[] fields = c.getDeclaredFields();
for (Field classField : fields)
{
result.add(classField);
}
}
DigitalOcean
digitalocean.com › community › tutorials › java-reflection-example-tutorial
Java Reflection Example Tutorial | DigitalOcean
August 3, 2022 - If the field is final, the set() methods throw java.lang.IllegalAccessException. We know that private fields and methods can’t be accessible outside of the class but using reflection we can get/set the private field value by turning off the java access check for field modifiers.
Baeldung
baeldung.com › home › java › core java › get all record fields and its values via reflection
Get All Record Fields and Its Values via Reflection | Baeldung
January 16, 2024 - But, it “upgraded” to a permanent feature in Java 16. The RecordComponent class provides information about a component of a record class. Moreover, the Class class provides the getRecordComponents() method to return all components of a record class if the class object is a Record instance. It’s worth noting that the components in the returned array are in the same order declared in the record. Next, let’s see how to use RecordComponent together with the reflection API to get all fields from our Player record class and the corresponding values of the ERIC instance:
GeeksforGeeks
geeksforgeeks.org › java › how-to-access-private-field-and-method-using-reflection-in-java
How to Access Private Field and Method Using Reflection in Java? - GeeksforGeeks
February 5, 2021 - // Access Private Field Using Reflection in Java import java.lang.reflect.Field; // Student class declaration class Student { // private fields private String name; private int age; // Constructor public Student(String name, int age) { this.name = name; this.age = age; } // Getters and setters public String getName() { return name; } public void setName(String name) { this.name = name; } private int getAge() { return age; } public void setAge(int age) { this.age = age; } // Override toString method to get required // output at terminal @Override public String toString() { return "Employee [nam
Coderanch
coderanch.com › t › 378770 › java › reflection-final-static-field
Using reflection to get the value of a final static field (Java in General forum at Coderanch)
January 5, 2006 - In order to do this it needs to call the stored procedure with parameters extracted from an xml file. I've given each parameter an attribute sqltype which should take the name of one of the fields of java.sql.Types and then I'm using reflection to get the actual value of that field.
noredhomepage
noredhomepage.weebly.com › java-reflection-get-field-value-from-object.html
Java reflection get field value from object - noredhomepage
In order to access a private field ... of a public field, you can call the get() method of the Field object, with the object featuring the field value that you'd like to get as the first parameter....
Coderanch
coderanch.com › t › 443479 › java › Property-Field-Reflection
get Property-Field-Name via Reflection (Java in General forum at Coderanch)
April 30, 2009 - The answer is that there doesn't have to be any such field, by any name, so reflection cannot help you. For example, getX() might look like Even if the method returns a variable, it might be named "variableX" or "valueOfX" or anything; or it might be an element of an array, or a value in a HashMap, or a variety of other things. If you need to find this out about one particular class, you can disassemble it with the "javap" tool and look at the bytecode to see how the method is implemented.
Jaketrent
jaketrent.com › post › use-java-reflection-get-field-w-accessor
Use Java Reflection to Get Field w/ Accessor
The only stipulation to this working is that the class follows the JavaBean naming convention standard of "get" + capitalized field name following. Oh, and one more: this is only designed for @Entity's with one @Id field (no composite key). This method goes through all fields, finds the one with the javax.persistence.Id interface annotation, then tries to find a matching accessor method. If it is found, it is executed, the value of the id field is given, finally to be used to create the specially formatted string.
Spring
docs.spring.io › spring-framework › docs › 3.2.x › javadoc-api › org › springframework › core › annotation › AnnotationUtils.html
AnnotationUtils (Spring Framework 3.2.18.RELEASE API)
the Map of annotation attributes, ... as values · public static AnnotationAttributes getAnnotationAttributes(Annotation annotation, boolean classValuesAsString, boolean nestedAnnotationsAsMap) Retrieve the given annotation's attributes as an AnnotationAttributes map structure. Implemented in Spring 3.1.1 to provide fully recursive annotation reading capabilities on par with that of the reflection-based ...
Reddit
reddit.com › r/learnjava › what’s the point of java reflection?
r/learnjava on Reddit: What’s the point of Java reflection?
September 5, 2022 -
I just watched a video showing some uses of reflection in Java, but honestly I can’t seem to comprehend why you’d go through that route with any program. For example, it was showing how you could alter the value of a final and/or private field. But what’s the point of adding 3+ extra lines of code when you could just change the type of the field?
Im not a Java veteran, but based on what I know, the concept of reflection seems unnecessary to me. Especially when the man who made the video, had as no1 argument as to why you should you use reflection that “it’s really cool”.
That’s why I’d like someone to briefly explain how it could genuinely be useful. Like, are there are any benefits that we couldn’t have without it ? In the video I watched there was something mentioned about frameworks which I haven’t worked with whatsoever, but I’m guessing that you’re still manipulating the api to get things done in a “cool” way.
Thank you in advance.
Top answer 1 of 9
9
In your normal applications you rarely use reflection yourself. It usually really is just a last resort thing to do if you need to get or set the value of a private field in a class that you need to extend. As the video you mentioned stated: The big use of reflection is in frameworks. Frameworks will use reflection to manipulate instances. They will allow you to use dependency injection, so that you dont need to care about where the required instances are coming from, you just get them and can use them. They will create and register event handlers based on annotations without you having to write any line of code besides the one annotation. Database frameworks will not make you deal with SQL result sets, instead they will give you a list of entity instances that they created via reflection. The framework wasnt built to specifically handle your Person entity for example. It is just able to accept any kind of entity because it can manipulate them via reflection. So in general frameworks will use reflection, accept that they have to write more code, so that the users of the framework can write less code. They do it so that the framework is as generic as possible. If you have never worked on larger projects and with large frameworks then this might not all make sense, but trust me reflection plays a huge role in saving time.
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5
From a testing perspective, I read from a good book called “Working Effectively With Legacy Code” by Michael Feathers that it is best practice to not modify existing code in order to open up classes for testing. If you cant access these fields because they are marked private, reflection can be used to access these fields from outside the class. There can be regulatory reasons for not opening up fields for testing, and its better to not make edits to existing code if it can be avoided. EDIT: grammar
GraalVM
graalvm.org › jdk24 › reference-manual › native-image › metadata
GraalVM
Providing constant arguments in code is a preferred way to provide metadata as it requires no duplication of information in external JSON files. Reflection in Java starts with java.lang.Class that allows fetching further reflective elements such as methods and fields.
Kotlin Discussions
discuss.kotlinlang.org › language design
Access Java field directly instead of using getter/setter - Language Design - Kotlin Discussions
October 4, 2020 - For example, here is a Java class public class Thing { ... public int thing; public getThing() { return thing; } public setThing(int t) { thing = t; } } In Kotlin, if I want to access thing , I would do the following: val t = Thing() t.thing ...