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

Question

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

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something like this should work     String name    Test2    Name of the class         Class myClass   Class forName name           Object o   myClass newInstance

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use Class forName  String name of class   newInstance     Class forName  A   newInstance      This will cause class named A initialized

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Class forName  ClassName   will solve your purpose   Class class1   Class forName ClassName   Object object1   class1 newInstance

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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

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MyClass myInstance    MyClass  Class forName  MyClass   newInstance

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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 lt   gt  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

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String str    String Class forName  java lang String   newInstance

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Using newInstance   directly is deprecated as of Java 8  You need to use Class getDeclaredConstructor      newInstance      with the corresponding exceptions

User · Answer

Two ways   Method 1 - only for classes having a no-arg constructor  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    For example   Class lt   gt  clazz   Class forName  java util Date    Object date   clazz newInstance      Method 2  An alternative safer approach which also works if the class doesn t have any no-arg constructors is to query your class object to get its Constructor object and call a newInstance   method on this object   Class lt   gt  clazz   Class forName  com foo MyClass    Constructor lt   gt  constructor   clazz getConstructor String class  Integer class   Object instance   constructor newInstance  stringparam   42     Both methods are known as reflection  You will typically have to catch the various exceptions which can occur  including things like    the JVM can t find or can t load your class the class you re trying to instantiate doesn t have the right sort of constructors the constructor itself threw an exception the constructor you re trying to invoke isn t public a security manager has been installed and is preventing reflection from occurring

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

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