How do I pass a class as a parameter in Java?
JavaClassGwtParametersJava Problem Overview
Is there any way to pass class as a parameter in Java and fire some methods from that class?
void main()
{
callClass(that.class)
}
void callClass(???? classObject)
{
classObject.somefunction
// or
new classObject()
//something like that ?
}
I am using Google Web Toolkit and it does not support reflection.
Java Solutions
Solution 1 - Java
public void foo(Class c){
try {
Object ob = c.newInstance();
} catch (InstantiationException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
}
}
How to invoke method using reflection
import java.lang.reflect.*;
public class method2 {
public int add(int a, int b)
{
return a + b;
}
public static void main(String args[])
{
try {
Class cls = Class.forName("method2");
Class partypes[] = new Class[2];
partypes[0] = Integer.TYPE;
partypes[1] = Integer.TYPE;
Method meth = cls.getMethod(
"add", partypes);
method2 methobj = new method2();
Object arglist[] = new Object[2];
arglist[0] = new Integer(37);
arglist[1] = new Integer(47);
Object retobj
= meth.invoke(methobj, arglist);
Integer retval = (Integer)retobj;
System.out.println(retval.intValue());
}
catch (Throwable e) {
System.err.println(e);
}
}
}
Also See
Solution 2 - Java
public void callingMethod(Class neededClass) {
//Cast the class to the class you need
//and call your method in the class
((ClassBeingCalled)neededClass).methodOfClass();
}
To call the method, you call it this way:
callingMethod(ClassBeingCalled.class);
Solution 3 - Java
Construct your method to accept it-
public <T> void printClassNameAndCreateList(Class<T> className){
//example access 1
System.out.print(className.getName());
//example access 2
ArrayList<T> list = new ArrayList<T>();
//note that if you create a list this way, you will have to cast input
list.add((T)nameOfObject);
}
Call the method-
printClassNameAndCreateList(SomeClass.class);
You can also restrict the type of class, for example, this is one of the methods from a library I made-
protected Class postExceptionActivityIn;
protected <T extends PostExceptionActivity> void setPostExceptionActivityIn(Class <T> postExceptionActivityIn) {
this.postExceptionActivityIn = postExceptionActivityIn;
}
For more information, search Reflection and Generics.
Solution 4 - Java
Use
void callClass(Class classObject)
{
//do something with class
}
A Class
is also a Java object, so you can refer to it by using its type.
Read more about it from official documentation.
Solution 5 - Java
This kind of thing is not easy. Here is a method that calls a static method:
public static Object callStaticMethod(
// class that contains the static method
final Class<?> clazz,
// method name
final String methodName,
// optional method parameters
final Object... parameters) throws Exception{
for(final Method method : clazz.getMethods()){
if(method.getName().equals(methodName)){
final Class<?>[] paramTypes = method.getParameterTypes();
if(parameters.length != paramTypes.length){
continue;
}
boolean compatible = true;
for(int i = 0; i < paramTypes.length; i++){
final Class<?> paramType = paramTypes[i];
final Object param = parameters[i];
if(param != null && !paramType.isInstance(param)){
compatible = false;
break;
}
}
if(compatible){
return method.invoke(/* static invocation */null,
parameters);
}
}
}
throw new NoSuchMethodException(methodName);
}
Update: Wait, I just saw the gwt tag on the question. You can't use reflection in GWT
Solution 6 - Java
Adding <T> T as return type worked for me. Ex with json deserialize
public static <T> T fromJson(String json, Class<T> classOfT){
return gson().fromJson(json, classOfT);
}
Solution 7 - Java
I am not sure what you are trying to accomplish, but you may want to consider that passing a class may not be what you really need to be doing. In many cases, dealing with Class like this is easily encapsulated within a factory pattern of some type and the use of that is done through an interface. here's one of dozens of articles on that pattern: http://today.java.net/pub/a/today/2005/03/09/factory.html
using a class within a factory can be accomplished in a variety of ways, most notably by having a config file that contains the name of the class that implements the required interface. Then the factory can find that class from within the class path and construct it as an object of the specified interface.
Solution 8 - Java
As you said GWT does not support reflection. You should use deferred binding instead of reflection, or third party library such as gwt-ent for reflection suppport at gwt layer.
Solution 9 - Java
Se these: http://download.oracle.com/javase/tutorial/extra/generics/methods.html
here is the explaniation for the template methods.
Solution 10 - Java
Have a look at the reflection tutorial and reflection API of Java:
https://community.oracle.com/docs/DOC-983192[enter link description here]1
and
http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html
Solution 11 - Java
Class as paramater. Example.
Three classes:
class TestCar {
private int UnlockCode = 111;
protected boolean hasAirCondition = true;
String brand = "Ford";
public String licensePlate = "Arizona 111";
}
--
class Terminal {
public void hackCar(TestCar car) {
System.out.println(car.hasAirCondition);
System.out.println(car.licensePlate);
System.out.println(car.brand);
}
}
--
class Story {
public static void main(String args[]) {
TestCar testCar = new TestCar();
Terminal terminal = new Terminal();
terminal.hackCar(testCar);
}
}
In class Terminal method hackCar() take class TestCar as parameter.