![]() ![]() This tutorial will focus on how to retrieve the fields of a Java class, including private and inherited fields. It allows us to inspect the elements of a class such as fields, methods or even inner classes, all at runtime. In this tutorial, weve seen how we can modify or set the values of private fields of a class from another class in Java. In this example, we will try to access the private field defined in the other class. In Java, we achieve this by using the Java Reflection API. Through reflection we can access the private variables and methods of a class with the help of its class object and invoke the method by using the object as. Reflection1.We can access private fields and methods outside of class using reflection. An object cant use it to find out about data fields that it wouldnt normally be able to access (for example, another objects private fields), and you cant. Here is following code snapts to demonstrate basic concepts of Reflection If you want to invoke any method using reflection, you can go through invoke method using reflection. Reflective code breaks abstractions and therefore may change behavior with upgrades of the platform" When the value of a private field is always assigned to in a class methods before being read, then it is not being used to. "Since reflection allows code to perform operations that would be illegal in non-reflective code, such as accessing private fields and methods, the use of reflection can result in unexpected side-effects, which may render code dysfunctional and may destroy portability. But as per the Oracle documentation in the section drawbacks they recommended that : ![]() setAccessible(true) // get the value of this private field String. Using the Reflection in Java you can access all the private/public fields and methods of one class to another. With reflections, we can get the information about any classs structure like its. The RuntimeExceptions which may be thrown are either SecurityExceptions (if the JVM's SecurityManager will not allow you to change a field's accessibility), or IllegalArgumentExceptions, if you try and access the field on an object not of the field's class's type: f.get("BOB") //will throw IllegalArgumentException, as String is of the wrong type To get the value of a public field, you can call the get() method of the Field object, with the object featuring the field value that youd like to get as the. The IllegalAccessException would be thrown if the field was not accessible (for example, if it is private and has not been made accessible via missing out the f.setAccessible(true) line. class.getField(1st) Class<> t f.getType() if(t.obj.getClass().getDeclaredField("misspelled") //will throw NoSuchFieldException Getting value of public static final field/property of a class in Java via reflection. Whereas Class.getDeclaredMethod(String methodName, Class<> parameterTypes) or Class.getDeclaredMethods() can be used to get private methods.Class.getDeclaredField(String fieldName) or Class.getDeclaredFields() can be used to get private fields. The NoSuchFieldException would be thrown if you asked for a field by a name which did not correspond to a declared field. If we want to access Private Field and method using Reflection we just need to call setAccessible(true) on the field or method object which you want to access. ![]() Method 3: Class.getDeclaredField(FieldName): Used to get the private field. We use below two methods for this purpose. Hashtable iWantThis = (Hashtable) f.get(obj) //IllegalAccessExceptionĮDIT: as has been commented by aperkins, both accessing the field, setting it as accessible and retrieving the value can throw Exceptions, although the only checked exceptions you need to be mindful of are commented above. Note: Through reflection, we can access the private variables and methods of a class with the help of its class object and invoke the method by using the object as discussed above. In order to access private fields, you need to get them from the class's declared fields and then make them accessible: Field f = obj.getClass().getDeclaredField("stuffIWant") //NoSuchFieldException ![]()
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