Question

I have a class name (as a String), and I want to get all members and their types. I know I need to use reflection, but how?

For instance, if I have

class MyClass {
    Integer a;
    String b;
}

how do I get the types and names of a and b?

Answer 1

If the classes have already been loaded by the jvm, you can use the static method of Class called Class.forName(String className); and it will return you a handle to the reflections object.

you would do:

//get class reflections object method 1
Class aClassHandle = Class.forName("MyClass");

//get class reflections object method 2(preferred)
Class aClassHandle = MyClass.class;

//get a class reflections object method 3: from an instance of the class
MyClass aClassInstance = new MyClass(...);
Class aClassHandle = aClassInstance.getClass();



//get public class variables from classHandle
Field[] fields = aClassHandle.getFields();

//get all variables of a class whether they are public or not. (may throw security exception)
Field[] fields = aClassHandle.getDeclaredFields();

//get public class methods from classHandle
Method[] methods = aClassHandle.getMethods();

//get all methods of a class whether they are public or not. (may throw security exception)
Method[] methods = aClassHandle.getDeclaredMethods();

//get public class constructors from classHandle
Constructor[] constructors = aClassHandle.getConstructors();

//get all constructors of a class whether they are public or not. (may throw security exception)
Constructor[] constructors = aClassHandle.getDeclaredConstructors();

To get a variable named b from MyClass, one might do.

Class classHandle = Class.forName("MyClass");
Field b = classHandle.getDeclaredField("b");

and if b is type integer, to get its value i would do.

int bValue = (Integer)b.get(classInstance);//if its an instance variable`

or

int bValue = (Integer)b.get(null);//if its a static variable