CODEWITHSUNDEEP
javajakarta-ee
hawx
hawx

Reputation: 1669

Invoking a Class and Method Using Variables In Java

I am attempting to call a custom class and method on my Application start-up to perform dev testing. I have stored the setting for my test class and method in my SettingsClass as shown below.

public class SettingsClass {

        public static final boolean BOOT_TEST = true;
        public static final String BOOT_CLASS = "MyClass";
        public static final String BOOT_METHOD = "MyMethod";

    }

My Main Class.

public class MainClass {


        public static void main(String[] args) throws InstantiationException, IllegalAccessException, ClassNotFoundException {

            if(SettingsClass.BOOT_TEST) {
                Method method = getDeclaredMethodClass(SettingsClass.BOOT_CLASS).getDeclaredMethod(SettingsClass.BOOT_METHOD);
                method.invoke();
                System.exit(1);
            }
}

Is it possible to perform the above action?

Any help would be appreciated.

Upvotes: 2

Views: 2389

Answers (4)

Kallja
Kallja

Reputation: 5472

Yes, it is. The following code will execute the method someMethod in the MainClass.

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class MainClass {

  public static final boolean BOOT_TEST = true;
  public static final String BOOT_CLASS = "MainClass";
  public static final String BOOT_METHOD = "someMethod";

  public static void main(String[] args) throws InstantiationException,
      IllegalAccessException, ClassNotFoundException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException, SecurityException {

    if (MainClass.BOOT_TEST) {
      Class bootClass = Class.forName(BOOT_CLASS);
      Method bootMethod = bootClass.getDeclaredMethod(BOOT_METHOD, null);
      bootMethod.invoke(null, null);
    }
  }

  public static void someMethod() {
    System.out.println("Some method executing...");
  }
}

What you need to do is get the class object for the class whose method you wish to execute dynamically by using the static method Class.forName(String) passing in the class's name. subsequently you can request the method you wish to execute using the getDeclaredMethod(String, Class<?>...) passing in the method's name and parameter types. Following that you can call invoke(Object, Object...) on the method with two null arguments (execute the method on no instance of the class (static execution) without any parameters).

Upvotes: 1

Bhaskar
Bhaskar

Reputation: 592

You need both a reference to the Class type and an instance of the class (unless the method you want to invoke is static). In your pseudo code you have the correct idea, all you need to do is a quick review of the javadoc for java.lang.Class and java.lang.reflect.Method

public class SettingsClass {

    public static final boolean BOOT_TEST = true;
    public static final String BOOT_CLASS = "MyClass";
    public static final String BOOT_METHOD = "doMain";

}

public class MyClass {
    public static void doMain() {
    }
}

public class MainClass {


    public static void main(String[] args) throws InstantiationException, IllegalAccessException, ClassNotFoundException {

        if(SettingsClass.BOOT_TEST) {
            Class<?> clazz = Class.forName(SettingsClass.BOOT_CLASS);
            Method m = clazz.getMethod(SettingsClass.BOOT_METHOD);
            m.invoke(null);
            System.exit(1);
        }

}

Upvotes: 3

venergiac
venergiac

Reputation: 7717

You can refer to Java reflection (Method Invocation)

http://docs.oracle.com/javase/tutorial/reflect/member/methodInvocation.html

you can find methods through

Class<?> c = Class.forName("nameClass");
Object t = c.newInstance();

Method[] allMethods = c.getDeclaredMethods();

and you can call through

m.setAccessible(true);
Object o = m.invoke(t, .... )

Upvotes: 1

Dodge
Dodge

Reputation: 8307

for .invoke() you need an object that is an instance of your class.

if your class has an public default consturctor you should be able to do something like this

// load your class
Class<?> clazz = Class.forName("full.package.and.class.name"); 
// get the method
Method method = clazz.getDeclaredMethod("methodName");
// create an instance of your class
Object object = clazz.newInstance();
// call the method in context of object
method.invoke(object);

Upvotes: 2

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