How do I invoke a Java method when given the method name as a string?

2021-6-3 anglehua

If I have two variables:

Object obj;
String methodName = "getName";

Without knowing the class of obj, how can I call the method identified by methodName on it?

The method being called has no parameters, and a String return value. It's a getter for a Java bean.


Coding from the hip, it would be something like:

java.lang.reflect.Method method;
try {
  method = obj.getClass().getMethod(methodName, param1.class, param2.class, ..);
} catch (SecurityException e) { ... }
  catch (NoSuchMethodException e) { ... }

The parameters identify the very specific method you need (if there are several overloaded available, if the method has no arguments, only give methodName).

Then you invoke that method by calling

try {
  method.invoke(obj, arg1, arg2,...);
} catch (IllegalArgumentException e) { ... }
  catch (IllegalAccessException e) { ... }
  catch (InvocationTargetException e) { ... }

Again, leave out the arguments in .invoke, if you don't have any. But yeah. Read about Java Reflection



Use method invocation from reflection:

Class<?> c = Class.forName("class name");
Method method = c.getDeclaredMethod("method name", parameterTypes);
method.invoke(objectToInvokeOn, params);

Where:

  • "class name" is the name of the class
  • objectToInvokeOn is of type Object and is the object you want to invoke the method on
  • "method name" is the name of the method you want to call
  • parameterTypes is of type Class[] and declares the parameters the method takes
  • params is of type Object[] and declares the parameters to be passed to the method


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