Java reflection set private field
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We then cast the result to the required type. If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned. The following steps show how to use it.
You can read its name, access modifiers etc. Primitive types are — boolean, byte, short, int, long, char, float, and double. Access specifiers such as protected and private are not meant as security measures, to make data invisible under all circumstances. Obtain a Field object for that field, make it accessible and update it.
Though it works, it looks so weird to me, I suspect rather a bug than a feature! This means that with this method, we can get public methods of the java. Here is the Person class: public class Person private String name; private int age; We will now use java reflection to discover the names of all fields of this class. Field Declaring Class We can use getDeclaringClass of field object to get the class declaring the field. For instance, in many cases we have a naming convention for database tables. We need to pass class instance and required arguments. In this article we will see simple example of accessing private field using reflection and invoking private method using reflection in Java. Implemented Interfaces Using java reflection, we are also able to get the list of interfaces implemented by a given class. Matthiew You are right of course!
Java reflection get set private field value - We will look into this in more details in later sections.
I have a class with a private static final field that, unfortunately, I need to change at run-time. Using reflection I get this error: java. IllegalAccessException: Can not set static final boolean field Is there any way to change the value. Here's an example: import java. It may not work because a SecurityManager may be present, but even if it doesn't, depending on usage pattern, it may or may not work. In some cases, such as deserialization, the system will need to change the final fields of an object after construction. The only pattern in which this has reasonable semantics is one in which an object is constructed and then the final fields of the object are updated. The object should not be made visible to other threads, nor should the final fields be read, until all updates to the final fields of the object are complete. Freezes of a final field occur both at the end of the constructor in which the final field is set, and immediately after each modification of a final field via reflection or other special mechanism. Even then, there are a number of complications. If a final field is initialized to a compile-time constant in the field declaration, changes to the final field may not be observed, since uses of that final field are replaced at compile time with the compile-time constant. Another problem is that the specification allows aggressive optimization of final fields. Within a thread, it is permissible to reorder reads of a final field with those modifications of a final field that do not take place in the constructor. Does your code looks like this. For more details about why this behavior. My answer only shows how, in some circumstances, this is possible. The most disgusting example that I can think of is deliberate chosen with the hope that perhaps people would be instantly disgusted by instead of falling in love with java reflection set private field technique. Fields of primitive or String type can be compile-time constants. A constant will be inlined in any code that references the field. Since the field is not actually read at runtime, changing it then will have no effect. The says this: If a field is a constant variable §4. This is true even if the usage itself is not a compile-time constant expression §15. We refer to these fields as being write-protected to distinguish them from ordinary final fields. Source: In case of presence of a Security Manager, one can make use of AccessController. Apache commons FieldUtils class already has particular method that can do the stuff. Please, take a look at FieldUtils. You should specify target field instance and accessibility forcing flag if you play with non-public fields. More info you can find. Then I realized it failed at field. Probably the read caused somehow different setup of Java reflection internals namely sun. UnsafeQualifiedStaticObjectFieldAccessorImpl in java reflection set private field case instead of sun. UnsafeStaticObjectFieldAccessorImpl in success case but I didn't elaborate it further. However for general case this would not be sufficient. Just saw that question on one of the interview question, if possible to change final variable with reflection or in runtime. So in the main class import java. Class name: class SomeClass Value: There you are Process finished with exit code 0 According to documentation Tom: Did you ever read up why singletons are evil. Now I know that they evil only in Java. And only because of the availabilty of a user defined class loader. And ever since I know all this and I don´t use user defined class loader I use singletons without regret. And so does Scala where singleton are a first class language feature — That singletons are evil is is a well known false myth. They add hidden complexity to your code. Additionally, they can make it impossible to unit test without also knowing that n singletons must also be configured first. They are the antithesis of dependency injection. Your team might make the decision that the pitfalls of having hidden complexity don't outweigh the convenience of Singletons, but many teams take the opposite stance for good reason.
