How to inspect constructors, fields and methods using Reflection ?

Inspecting Constructors

Instantiating Objects using Constructor Object

// Get constructor that takes a String as argument

Constructor constructor = 

        MyObject.class.getConstructor(String.class);

MyObject myObject = 

       (MyObject) constructor.newInstance("constructor-arg1");

Get parameter types of constructor

Class[] parameterTypes = constructor.getParameterTypes();

Inspecting fields

If you know the name of the field you want to access, you can access it like this :

Field field = aClass.getField("someField");

If no field exists with the name given as parameter to the getField() method, a NoSuchFieldException is thrown.

Get field name and type

String fieldName = field.getName();

Object fieldType = field.getType();

Get and set values using the field.get() and field.set() methods

Object value = field.get(objectInstance);

field.set(objetInstance, value);

Inspecting methods

Return the public method named "doSomething", in the given class which takes a String as parameter

Method method = 

         aClass.getMethod("doSomething", new Class[]{String.class});

If no method matches the given method name and arguments, in this case String.class, a NoSuchMethodException is thrown.

If the method you are trying to access takes no parameters, pass null as the parameter type array :

Method method = aClass.getMethod("doSomething", null);

Get parameter types and return types

Class[] parameterTypes = method.getParameterTypes();

Class returnType = method.getReturnType();

Invoking method

Object returnValue = method.invoke(null, "parameter-value1");

If the method is static you supply null instead of an object instance.

If method is not static, you need to supply a valid instance on which you like to invoke it.