如果有两个变量:

Object obj;
String methodName = "getName";

在不知道obj的类的情况下,我如何调用由methodName识别的方法?

被调用的方法没有参数,只有一个String返回值。它是Java bean的getter。


当前回答

如果多次调用,则可以使用Java 7中引入的新方法句柄。现在我们开始你的方法返回一个字符串:

Object obj = new Point( 100, 200 );
String methodName = "toString";  
Class<String> resultType = String.class;

MethodType mt = MethodType.methodType( resultType );
MethodHandle methodHandle = MethodHandles.lookup().findVirtual( obj.getClass(), methodName, mt );
String result = resultType.cast( methodHandle.invoke( obj ) );

System.out.println( result );  // java.awt.Point[x=100,y=200]

其他回答

您应该使用reflection - init一个类对象,然后是该类中的一个方法,然后在具有可选参数的对象上调用此方法。记住将下面的代码段封装在try-catch块中

希望能有所帮助!

Class<?> aClass = Class.forName(FULLY_QUALIFIED_CLASS_NAME);
Method method = aClass.getMethod(methodName, YOUR_PARAM_1.class, YOUR_PARAM_2.class);
method.invoke(OBJECT_TO_RUN_METHOD_ON, YOUR_PARAM_1, YOUR_PARAM_2);
Method method = someVariable.class.getMethod(SomeClass);
String status = (String) method.invoke(method);

SomeClass是类,somvariable是变量。

为了完成我同事的回答,你可能需要密切关注以下问题:

static or instance calls (in one case, you do not need an instance of the class, in the other, you might need to rely on an existing default constructor that may or may not be there) public or non-public method call (for the latter,you need to call setAccessible on the method within an doPrivileged block, other findbugs won't be happy) encapsulating into one more manageable applicative exception if you want to throw back the numerous java system exceptions (hence the CCException in the code below)

下面是一个旧的java1.4代码,它考虑了这些要点:

/**
 * Allow for instance call, avoiding certain class circular dependencies. <br />
 * Calls even private method if java Security allows it.
 * @param aninstance instance on which method is invoked (if null, static call)
 * @param classname name of the class containing the method 
 * (can be null - ignored, actually - if instance if provided, must be provided if static call)
 * @param amethodname name of the method to invoke
 * @param parameterTypes array of Classes
 * @param parameters array of Object
 * @return resulting Object
 * @throws CCException if any problem
 */
public static Object reflectionCall(final Object aninstance, final String classname, final String amethodname, final Class[] parameterTypes, final Object[] parameters) throws CCException
{
    Object res;// = null;
    try {
        Class aclass;// = null;
        if(aninstance == null)
        {
            aclass = Class.forName(classname);
        }
        else
        {
            aclass = aninstance.getClass();
        }
        //Class[] parameterTypes = new Class[]{String[].class};
    final Method amethod = aclass.getDeclaredMethod(amethodname, parameterTypes);
        AccessController.doPrivileged(new PrivilegedAction() {
    public Object run() {
                amethod.setAccessible(true);
                return null; // nothing to return
            }
        });
        res = amethod.invoke(aninstance, parameters);
    } catch (final ClassNotFoundException e) {
        throw new CCException.Error(PROBLEM_TO_ACCESS+classname+CLASS, e);
    } catch (final SecurityException e) {
        throw new CCException.Error(PROBLEM_TO_ACCESS+classname+GenericConstants.HASH_DIESE+ amethodname + METHOD_SECURITY_ISSUE, e);
    } catch (final NoSuchMethodException e) {
        throw new CCException.Error(PROBLEM_TO_ACCESS+classname+GenericConstants.HASH_DIESE+ amethodname + METHOD_NOT_FOUND, e);
    } catch (final IllegalArgumentException e) {
        throw new CCException.Error(PROBLEM_TO_ACCESS+classname+GenericConstants.HASH_DIESE+ amethodname + METHOD_ILLEGAL_ARGUMENTS+String.valueOf(parameters)+GenericConstants.CLOSING_ROUND_BRACKET, e);
    } catch (final IllegalAccessException e) {
        throw new CCException.Error(PROBLEM_TO_ACCESS+classname+GenericConstants.HASH_DIESE+ amethodname + METHOD_ACCESS_RESTRICTION, e);
    } catch (final InvocationTargetException e) {
    throw new CCException.Error(PROBLEM_TO_ACCESS+classname+GenericConstants.HASH_DIESE+ amethodname + METHOD_INVOCATION_ISSUE, e);
    } 
    return res;
}

从反射使用方法调用:

Class<?> c = Class.forName("class name");
Method method = c.getDeclaredMethod("method name", parameterTypes);
method.invoke(objectToInvokeOn, params);

地点:

“class name”是类的名称 objectToInvokeOn类型为Object,是您希望在其上调用方法的对象 "method name"是你想要调用的方法的名称 parameterTypes的类型是Class[],声明方法所接受的参数 params类型为Object[],声明要传递给方法的参数

try {
    YourClass yourClass = new YourClass();
    Method method = YourClass.class.getMethod("yourMethodName", ParameterOfThisMethod.class);
    method.invoke(yourClass, parameter);
} catch (Exception e) {
    e.printStackTrace();
}