Java Reflection for creating new objects

Question

Is there a way to create primitive data type variables use Java Reflection?

For example,

public Object createObj(String type, String value){
  if(type.compareTo("char") == 0)
    //return a char
  else if(type.compareTo("int") == 0)
    //return an int
  ....
}

Answer 1

The common idiom I see here is to use Class.forName() .

public static Object makeNew(String type) throws Exception {
    Class clazz = Class.forName(type);
    return clazz.newInstance();
}

For int , char you have to use the names of their respective class-types, you can't actually make a primitive. "java.lang.Integer", "java.lang.Character", etc. respectively. You'll need to check those specially if you want to pass in "int", "char", etc.

Adding a "value" as a string is much harder. Most classes will not have a way of changing a string into an initial state. You'll definitely have to special case the primitives to provide an initial value. Overall, I think this is not a great way to approach whatever problem you are tying to solve.

---

So you mention in your comment about using setter methods. One problem is how do you determine which setter do you call? If you pass a parameter of "10", for a JButton , is that the setAlignmentX , setAlignmentY , or the setText method?

At this point you have to go whole hog on it.

<class>
  <name>javax.swing.JButton</name>
  <set><method>setAlignmentX</method><value>10</value></set>
</class>

Now you have the problem that some setters take other classes as parameters. And some classes are immutable ( Integer and Character are), they have no setters at all, you'll have to call a ctor.

You're basically getting into serialization here (which is a very hard problem). Take a look at XmlEncoder and XmlDecoder , they do something close to what you want. https://docs.oracle.com/javase/8/docs/api/java/beans/XMLEncoder.html