java reflection calling a function

Question

I am using the java reflection to call an API from the .class . I see my function is the list of functions listed by the .getMethods() API . The no param version works fine but the parameterised version fails .

The compilation time call for the API was

public static class CapabilitiesEditor  extends ComboBoxPropertyEditor  {
    public CapabilitiesEditor() {
        super();
        print(); // Call to print if fine . 
        setAvailableValues(new String[] { "High", "Medium", "Low", "None", }); // I want call this one . Fails
        Icon[] icons = new Icon[4];
        Arrays.fill(icons, UIManager.getIcon("Tree.openIcon"));
        setAvailableIcons(icons);
    }

Here is my code that attempts to change the setAvailableValues dynamically.

 Class<?> cls;
    // Paremeterized call 
    Class[] paramObject = new Class[1]; 
    paramObject[0] = Object[].class; // Function takes a single parameter of type Object[]
    Object[] params = new String[] { "H", "M", "L", "N" };

    // no paramater version
    Class noparams[] = {};

    try { 

    cls = Class.forName("com.app.services.prop.system.SystemTopologyBean$CapabilitiesEditor");                                  Object obj = cls.newInstance();   

    for(Method method : cls.getMethods()){
        System.out.println("method = " + method.getName());
    }
    // WORKS
    Method method = cls.getDeclaredMethod("print", noparams);  
    method.invoke(obj, null);

    // **DOES NOT WORK** 
    Method method = cls.getDeclaredMethod("setAvailableValues", paramObject);
    method.invoke(obj, params);

    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException e2) {
                                // TODO Auto-generated catch block
                                e2.printStackTrace();
                            }

I always get the following exception

java.lang.NoSuchMethodException: com.app.services.prop.system.SystemTopologyBean$CapabilitiesEditor.setAvailableValues([Ljava.lang.Object;)

EDIT :

I follow Mkyong wonderful tutorial on reflection How To Use Reflection To Call Java Method At Runtime

Michael Krause · Answer 1 · 2014-10-03T04:28:32.420

1

To retrieve your method, and then invoke it, you'll need to do it like this:

Class cls = Class.forName("com.app.services.prop.system.SystemTopologyBean$CapabilitiesEditor");
Object obj = cls.newInstance();
Method method = cls.getDeclaredMethod("setAvailableValues", new Class[] {String[].class});
method.invoke(obj, new Object[] {new String[] {"Foo", "Bar"}});

edited Oct 03 '14 at 04:28

answered Oct 03 '14 at 04:14

Michael Krause

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score 0 · Answer 2 · edited May 23 '17 at 10:33

So there were two issues here that prevented me from access the function . Be careful I should have been using getMethod instead of getDeclaredMethod

See Using .getDeclaredMethod to get a method from a class extending another answer to know which one should be applicable.

Also be very careful in calling the method.invoke function especially the second parameter .

See How to call MethodInvoke - reflection and Michael's answer above for the correct way to call .

java reflection calling a function

2 Answers2