java dynamically create object based on string

And if you can't guarantee your class will provide a constructor that sets all the fields like your example TempStruct does, then I'll call it a day and grab a beer, because this approach is DOA. Class cls = Class.forName(fullPathOfTheClass); Use java reflection. Exercise 1: At some point in the future, change the format in a backwards incompatible way to incur someone's wrath. The syntax you showed - which isn't quite Java syntax - was probably trying to imply something much like that. + */ String formatValue(Field f) { String retval = null; String type = f.getClass().getName(); if (type.equals("String")) { try { String value = (String)f.get(f); if (value != null) { retval = "'" + value + "'"; } else { retval = "NULL"; } } catch (Exception e) { System.err.println("No such field: " + e.getMessage()); } } else if (type.equals("Integer")) { try { Integer value = (Integer)f.get(f); if (value != null) { retval = … In Java, we generally create objects using the new keyword or we use some DI framework e.g. Sometimes you have an object and you need to call a method, or a different method, depending on some condition. I have a List that contains data with String type -> ["classField1", "classField2", "classField3"] I have a method (myMethod(List list, String className)) that accept as parameter the List. I have a method (myMethod(List list, String className)) that accept as parameter the List. This interface initializes an empty JSON object model and provides methods to add name/value pairs to the object model and to return the resulting object. The methods in this class can be chained to add multiple name/value pairs to the object. This discussion is archived. You can have any number of rows or columns. Unfortunately, I feel it misses one important point: dynamic casting. How do I create a Java string from the contents of a file? // now I can use the object methods as usual A specific element in an array is accessed by its index. Assuming that works, we then invoke the constructor via reflection, wave the magic wand and say abracadabra. So please enhance as appropriate. Remember the String type in Java is immutable. You can achieve the same using List. I didn't think any other way to do it. We can map the common properties with the following Java class: class Product { String name; String category; // standard getters and setters } On top of that, we need an appropriate representation for the details object. innerClassName; Inner class names are delimited with $, not with a period. After that I want to set the fields of the class by using the data of the List. // Instantiate the object with the converted arguments. Since that’s is (very) relatively new, this post will try to fill that gap. This means that the class name is: MyTestClass$MyInnerTestClass. Maps let us store object instances with some kind of key. Note the conversion from String to some other type is effectively a form of deserialization, and so you're placing constraints on your clients (whoever is giving you the Strings) to provide their values in specific formats. Creating New Objects There is no equivalent to method invocation for constructors, because invoking a constructor is equivalent to creating a new object (to be the most precise, creating a new object involves both memory allocation and object construction). Actually, I have a method that accept only List of Strings, so by using reflection I convert the object to List of string, and after that I want to do the opposite. More discussions in Java Programming. If you do need to use a parametrized constructor, this is what you need to do: import java.lang.reflect. String fullPathOfTheClass = "" is so that the class name is not used directly in later declaration. The $ syntax is valid for class loading only. // Search for an "appropriate" constructor. String fullPathOfTheClass = "" MyTestClass myTestObject = new MyTestClass(); You cannot use MyTestClass directly anywhere in this code for it to be really dynamic. I can put an object in for id "123" and get it back later. Let's try it with an extremely contrived example: I used to have the same kind of problem and a hashMap turned out to be the solution for me. In this tutorial, we walk through the creation of a basic form that binds to a plain Java object, applies validation to the input fields, and dynamically changes based on the state of the form. Have a look at the Collections tutorial from Oracle to learn about collections. To tell you the whole story: The kind of system I would like to create is one where you can generate a form (with some fields) which then would automatically be mapped to a java object with the same name as the form name and the fields and their values as class variables. Note: The java.lang.String class provides a lot of methods to work on string. Due to the fact that I want to obtain dynamically the fields of the class, the result of the above is that I have to cast each String value of the list, to the type of each field of the class. Class cls = Class.forName(fullPathOfTheClass); Having the Class type, you need to use the newInstance() function. So we need a function that parses a String into the appropriate target type: Ugh. I was thinking that using: mysql_fetch_object() Reading the type attribute; Creating an object with type defined by type attribute If you wish to create a dynamic 2d array in Java without using List. In order to dynamically create an object in Java from an inner class name, you should use the $ sign. . How to read the value of a private field from a different class in Java? MyTestClass myTestObject = (MyTestClass) cls.newInstance(); Not if MyTestClass is an interface or super class, eh? Java String is not a primitive data type like int and long. Thereafter I would like to pass it to hibernate to store it in my DB. For example: private MyTestClass.MyInnerTestClass myInnerObject; For more information see: Overloaded constructors of the same arity? (generic type), JsonMappingException: No suitable constructor found for type[simple type, class]: can not instantiate from JSON object. I try to give a solution with the following way: Actually I want to create an object of an existing class and I tried to do that with reflection. This is ugly and handles only intrinsic types. What is the difference between canonical name, simple name and class name in Java Class? The static method forName() in the java.lang.Class class will return the Class object that represents a class, given its name as a String; then you can call newInstance() on the Class object to construct an instance of the class. This example creates an Hello class source, compiles it and calls a given method. Java 8 Object Oriented Programming Programming To declare array size dynamically read the required integer value from the user using Scanner class and create … Create an object from a string Tag(s): Language In this HowTo, we instantiate an object from its classname and pass a parameter to the constructor. Thread: How to create object dynamically with class name known in string format As with any other object, you can create String objects by using the new keyword and a constructor. Dynamically naming an object. myTestObject.myFunction(); In order to dynamically create an object in Java from an inner class name, you should use the $ sign. I have a List that contains data with String type -> ["classField1", "classField2", "classField3"]. fred rosenberger. That threw a lot of new stuff out there all at once. Simply load the class and search for a constructor whose number of parameters matches the number of arguments (i.e., arity). Please keep your hands inside the vehicle at all times as the ride is going to get bumpy. Dynamic instantiation of objects can get pretty complex, and your scenario touches upon several aspects: A thorough discussion of each of those points would take up an entire chapter in a no-doubt riveting treatment of Java as a dynamic language. It is basically an object that represents sequence of char values . I generally don't encourage dynamic forms. className + The String class has 11 constructors that allow you to provide the initial value of the string using different sources, such as an array of characters. then why don’t I just directly use: Send Page to a Friend. I am sure that the order of the Strings inside to the List, are in the right order, and correspond to the fields of the class with the same order. One of JSF's strengths is that instead of having to have programmers painstakingly create and debug the UI from logic (one of the annoying things about frameworks such as java awt), you can have non-JSF people "paint" a form in declarative View Template Language (xhtml) and let JSF do all the dirty work. The "Client client = " part is the object itself. Arrays store one or more values of a specific data type and provide indexed access to store the same. 2. I use the following code: But I get an exception to the 2nd line, when it tries to create the new object. the whole purpose of this exercise get defeated when you use… Okay, so I'm using a JButton to create an object for an inventory tracking software and I need a way to dynamically identify objects to avoid identifier conflicts. However, the parser will fail when the JSON data contains unknown properties. Arrays in Java are homogeneous data structures implemented in Java as objects. p. parbir. Defining a dynamic property using Object.defineProperty. There are two methods present in Reflection API which we can use to create objects A builder for creating JsonObject models from scratch. Java String Class represents character strings. And then, we are calling a method dynamically. It is like an array of characters works same as java string. Non-public constructors? 1. Jesper's Blog - Pluralsight Author Page . In this case, the formats are defined by the behavior of the parse methods. Take a look at the JavaDoc for Map. Nope, not gonna work. loading the right class from the class name and creating an instance. We store the dynamic properties in the details object. If the fully-qualified name of a class is available, it is possible to get the corresponding Class using the static method Class.forName(). Spring to create an object which internally use Java Reflection API to do so. If you want to create and store objects dynamically, you'll have to store them in a collection such as a List, Map or Set. See the below program. Voilà: you have a new object. Java Programming Forum - Learning Java easily. In this Article, we are going to study the reflective ways to create objects. Dynamically Create Object Based on String… For Example: String className = "MyTestClass"; Programming, Researching and Developing practice. Check it out: So String name = "a_class"; Class c = Class.forName(name); PreClass p = (PreClass) c.newInstance(); However, This cannot be used for primitive types. It uses the constructor represented by the class object to create and initialize a new instance of the constructor’s declaring class, with the specified initialization parameters. 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