I am trying implement the Data transformation using Reflection1 example in my code. The GetSourceValue function has a switch comparing various types, but I want to remove these types and properties and have GetSourceValue get the value of the property using only a single string as the parameter. I want to pass a class and … Read more
Due to the implementation of Java generics, you can’t have code like this: public class GenSet<E> { private E a[]; public GenSet() { a = new E[INITIAL_ARRAY_LENGTH]; // error: generic array creation } } How can I implement this while maintaining type safety? I saw a solution on the Java forums that goes like this: … Read more
What’s the best way to call a generic method when the type parameter isn’t known at compile time, but instead is obtained dynamically at runtime? Consider the following sample code – inside the Example() method, what’s the most concise way to invoke GenericMethod<T>() using the Type stored in the myType variable? public class Sample { … Read more
What is reflection, and why is it useful? I’m particularly interested in Java, but I assume the principles are the same in any language. 2 23 The name reflection is used to describe code which is able to inspect other code in the same system (or itself). For example, say you have an object of … Read more
The name reflection is used to describe code which is able to inspect other code in the same system (or itself). For example, say you have an object of an unknown type in Java, and you would like to call a ‘doSomething’ method on it if one exists. Java’s static typing system isn’t really designed … Read more
Java Reflection – Object is not an instance of declaring class
I have to ask a question in return: is your GenSet “checked” or “unchecked”? What does that mean? Checked: strong typing. GenSet knows explicitly what type of objects it contains (i.e. its constructor was explicitly called with a Class<E> argument, and methods will throw an exception when they are passed arguments that are not of type E. See Collections.checkedCollection.-> in that case, you should … Read more
After type erasure, all that is known about T is that it is some subclass of Object. You need to specify some factory to create instances of T. One approach could use a Supplier<T>: class MyClass<T> { private final Supplier<? extends T> ctor; private T field; MyClass(Supplier<? extends T> ctor) { this.ctor = Objects.requireNonNull(ctor); } public void myMethod() { field … Read more
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())) { … Read more
