Invoking a static method using reflection

JavaReflectionStatic

Java Problem Overview


I want to invoke the main method which is static. I got the object of type Class, but I am not able to create an instance of that class and also not able to invoke the static method main.

Java Solutions


Solution 1 - Java

// String.class here is the parameter type, that might not be the case with you
Method method = clazz.getMethod("methodName", String.class);
Object o = method.invoke(null, "whatever");

In case the method is private use getDeclaredMethod() instead of getMethod(). And call setAccessible(true) on the method object.

Solution 2 - Java

Fromthe Javadoc of Method.invoke():

If the underlying method is static, then the specified obj argument is ignored. It may be null.

What happens when you

Class klass = ...;
Method m = klass.getDeclaredMethod(methodName, paramtypes);
m.invoke(null, args)

Solution 3 - Java

String methodName= "...";
String[] args = {};

Method[] methods = clazz.getMethods();
for (Method m : methods) {
    if (methodName.equals(m.getName())) {
        // for static methods we can use null as instance of class
        m.invoke(null, new Object[] {args});
        break;
    }
}

Solution 4 - Java

public class Add {
    static int add(int a, int b){
        return (a+b);
    }
}

In the above example, 'add' is a static method that takes two integers as arguments.

Following snippet is used to call 'add' method with input 1 and 2.

Class myClass = Class.forName("Add");
Method method = myClass.getDeclaredMethod("add", int.class, int.class);
Object result = method.invoke(null, 1, 2);

Reference link.

Attributions

All content for this solution is sourced from the original question on Stackoverflow.

The content on this page is licensed under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.

Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionStevenView Question on Stackoverflow
Solution 1 - JavaAdeel AnsariView Answer on Stackoverflow
Solution 2 - JavaatkView Answer on Stackoverflow
Solution 3 - JavaFrostmanView Answer on Stackoverflow
Solution 4 - JavaHari KrishnaView Answer on Stackoverflow