Is there a way to instantiate a class by name in Java?

java get class instance from name
java dynamically create object based on string
object instantiation in java
dynamically name objects java
java create class from string
object obj = new object in java
java reflection
java dynamic class name

I was looking as the question : Instantiate a class from its string name which describes how to instantiate a class when having its name. Is there a way to do it in Java? I will have the package name and class name and I need to be able to create an object having that particular name.

Java - Dynamic Class Instantiation, Instantiation: The new keyword is a Java operator that creates the object. Note: The phrase "instantiating a class" means the same thing as "creating an object. The name of the constructor provides the name of the class to instantiate. If your class has a no-arg constructor, you can get a Class object using Class.forName() and use the newInstance() method to create an instance (though beware that this method is often considered evil because it can defeat Java’s checked exceptions).

MyClass myInstance = (MyClass) Class.forName("MyClass").newInstance();

Creating Objects (The Java™ Tutorials > Learning the Java , A powerful feature of JavaSW is to be able to instantiate a class using the String name of the class. If Java 'knows' about the class (ie, it exists somewhere in the  How to do custom rounding of numbers in Java? java,rounding. Math.floor(x+0.7) should do it. This should work for an arbitrary mantissa. Just add the offset to the next integer to your value and round down. The rounding is done by floor. Here is what the java API says to floor: Returns the largest (closest to positive infinity) double value that

use Class.forName("String name of class").newInstance();

Class.forName("A").newInstance();

This will cause class named A initialized.

How do I instantiate an object of a class via its String name?, You can create an object dynamically at runtime using only the name of the class, input as The most common use of reflection is to instantiate a class whose generic type is The object can then be used in the same way as any other object. Can Java class name contain underscore? Technically it’s possible to use the underscore in a class name, but there’s no practical reason to do so. If the underscore were used in a class name, it would act as a separator between words. In Java, we achieve optical separation between words with the camel case.

To make it easier to get the fully qualified name of a class in order to create an instance using Class.forName(...), one could use the Class.getName() method. Something like:

class ObjectMaker {
    // Constructor, fields, initialization, etc...
    public Object makeObject(Class<?> clazz) {
        Object o = null;

        try {
            o = Class.forName(clazz.getName()).newInstance();
        } catch (ClassNotFoundException e) {
            // There may be other exceptions to throw here, 
            // but I'm writing this from memory.
            e.printStackTrace();
        }

        return o;
    }
}

Then you can cast the object you get back to whatever class you pass to makeObject(...):

Data d = (Data) objectMaker.makeObject(Data.class);

Java Practices->Construct Object using class name, You will learn how to create a class later in Creating Classes. This statement creates a new Date object ( Date is a class in the java.util package). which simply declares to the compiler that the name today will be used to refer to an object whose To instantiate the Date class, or any other class, use the new operator. In Java programming, instantiating an object means to create an instance of a class. To instantiate an object in Java, follow these seven steps. Open your text editor and create a new file. Type in the following Java statements: The object you have instantiated is referred to as person.

Use java reflection

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). So the nearest equivalent to the previous example is to say:

import java.lang.reflect.*;

   public class constructor2 {
      public constructor2()
      {
      }

      public constructor2(int a, int b)
      {
         System.out.println(
           "a = " + a + " b = " + b);
      }

      public static void main(String args[])
      {
         try {
           Class cls = Class.forName("constructor2");
           Class partypes[] = new Class[2];
            partypes[0] = Integer.TYPE;
            partypes[1] = Integer.TYPE;
            Constructor ct 
              = cls.getConstructor(partypes);
            Object arglist[] = new Object[2];
            arglist[0] = new Integer(37);
            arglist[1] = new Integer(47);
            Object retobj = ct.newInstance(arglist);
         }
         catch (Throwable e) {
            System.err.println(e);
         }
      }
   }

which finds a constructor that handles the specified parameter types and invokes it, to create a new instance of the object. The value of this approach is that it's purely dynamic, with constructor lookup and invocation at execution time, rather than at compilation time.

Creating Objects, Instantiation: The new keyword is a Java operator that creates the object. variable in this manner, it could be illustrated as follows (variable name, plus  You have to write the code of the factory method as there is no standard way of creating a child class based on its parent class. It's always specific and depends on the logic of your classes. However, consider if it is really what you need. There are not many smart use cases for instantiating a class based on the instance of its parent.

15. Classes and Objects — the Basics, Every class should have a method with the special name __init__. from turtle import Turtle tess = Turtle() # Instantiate objects of type Turtle alex = Turtle()  @conorgriffin in a way yes, it moves the responsibilities from one place to another - but there's no escaping, at some place the objects need to be instantiated and it makes sense to put this code in each subclass; and on the other hand - a Java application can only have a single main() method, so it was necessary to get rid of the multiple main() methods. – Óscar López Apr 27 '14 at 19:11

Guide to Java Reflection, Additionally, we can instantiate new objects, invoke methods, and get or set To get access to the class, method, and field information of an instance we In such cases, we may name the Java object holding student data as  There is no Sample class in your code . The one which you have declared is a private method . // private method which takes an int as parameter and returns another int private int Sample(int c) { int a = 1; int b = 2; c = a + b; return c; } With the current snippet , You need to instantiate the Testing class and make use of the Sample method.

Class and object initialization in Java, Learn how to to initialize Java classes and objects for successful JVM The angle brackets prevent a name conflict: you cannot declare a  You can't write a program that uses an ordinary call to new to do that: in order for a class to be instantiated, it must have a name. Anonymous inner classes, as that term implies, do not have a name. Thus a class that exists within that anonymous inner class also has no name; thus it can not be instantiated outside of that anonymous inner class.

Comments
  • We instantiate a class and the result is an object (or: instance).
  • The answer is yes, but I think you should ask if its a good idea. With great power (reflection) comes great responsibility and you should only use it if you understand and have considered the consequences.
  • hi, once we have created the object from newInstance(), could we cast it back to our own object?
  • @Simon can you elaborate/give pointer about the security manager?
  • I don't understand this. I want to access a class in an unknown file in some other directory, I only have the name of the path/file as a string. String "dir/unkonwn.java". Calling Class.forName("dir/unknown") gives me errors.
  • How can we cast instance to com.foo.MyClass ? given that com.foo.MyClass is just a string
  • It's worth mentioning that this doesn't work if the class has no parameterless constructor (and has other constructors), or if the parameterless constructor is inaccessible.
  • DOesn't work for me, even with the package name prepended. :(
  • Can't you simply clazz.newInstance() instead of the getName then fromName?