Java – How to invoke a Java method when given the method name as a string

invokejavareflection

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.

Best Answer

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

Related Solutions

Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Java – How to efficiently iterate over each entry in a Java Map

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

On Java 10+:

for (var entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

Best Answer

Related Solutions

Java – What are the differences between a HashMap and a Hashtable in Java

Java – How to efficiently iterate over each entry in a Java Map

Related Topic