Question

I have 2 classes in my android app. Class1 and Class2. I have some methods in class2 which i want to invoke using reflection API.

To invoke “printString” of class2, i am using following code:

public void printString(String str) {
        Log.d("TAG", "in printString" + str);
    }

Reflection Code:

Method method = Class2.class.getMethod("printString");
method.invoke("asjdhaskdf", null);

But using this code is throwing following exception:

10-26 16:10:16.931: W/System.err(25036): java.lang.NoSuchMethodException: printString []
10-26 16:10:16.931: W/System.err(25036):    at java.lang.Class.getConstructorOrMethod(Class.java:460)
10-26 16:10:16.931: W/System.err(25036):    at java.lang.Class.getMethod(Class.java:915)
10-26 16:10:16.931: W/System.err(25036):    at com.sample.mobile.android.ui.activities.Class1Activity$1.onClick(Class1Activity.java:56)
10-26 16:10:16.931: W/System.err(25036):    at android.view.View.performClick(View.java:3627)
10-26 16:10:16.931: W/System.err(25036):    at android.view.View$PerformClick.run(View.java:14329)
10-26 16:10:16.936: W/System.err(25036):    at android.os.Handler.handleCallback(Handler.java:605)
10-26 16:10:16.936: W/System.err(25036):    at android.os.Handler.dispatchMessage(Handler.java:92)
10-26 16:10:16.936: W/System.err(25036):    at android.os.Looper.loop(Looper.java:137)
10-26 16:10:16.941: W/System.err(25036):    at android.app.ActivityThread.main(ActivityThread.java:4511)
10-26 16:10:16.941: W/System.err(25036):    at java.lang.reflect.Method.invokeNative(Native Method)
10-26 16:10:16.941: W/System.err(25036):    at java.lang.reflect.Method.invoke(Method.java:511)
10-26 16:10:16.941: W/System.err(25036):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:986)
10-26 16:10:16.941: W/System.err(25036):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:753)
10-26 16:10:16.941: W/System.err(25036):    at dalvik.system.NativeStart.main(Native Method)

Please advise what i am doing wrong. I have read tutorials available on internet but nothing worked.

Update 1

One Imp Point: My code never reached on “method.invoke” line. It throws an exception on the line where i am getting the method using “getMethod” function.

Code of Class2:

package com.sample.mobile.android.utils;

public class Class2{

    public void printString(String str) {
       Log.d("TAG", "in printString" + str);
    }

}

Code of class1Activity:

package com.sample.mobile.android.ui.activities;

public class Class1Activity extends Activity {

    private Class2 obj; 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        obj = new Class2();
        Class cls;
        try {
            cls = Class
                    .forName("com.sample.mobile.android.utils.Class2");

            Method[] methods = cls.getMethods();
            Log.d("TAG", "length -- " + methods.length);

            for (int i = 0; i < methods.length; i++) {
                Log.d("TAG", "name -- " + methods[i].getName());
                // this is printing the name of all  methods including "printString".
            }

            Method method = cls.getMethod("printString");
            method.invoke(obj, "asjdhaskdf");

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Answer 1

it because there is no such method

you’re trying invoke this method on String class

it should be method.invoke(instanceofClass2, "asjdhaskdf")

EDIT: to match Update 1

… and since printString has String parameters you should use getMethod like this:

Method method = Class2.class.getMethod("printString", String.class);