如果我有两个变量：
Object obj;
String methodName = "getName";
在不知道obj类的情况下，如何在其上调用methodName标识的方法？
被调用的方法没有参数，并且String返回值。它是 Java bean的getter 。
答案 0 :(得分：904)
从臀部编码，它会是这样的：
java.lang.reflect.Method method;
try {
method = obj.getClass().getMethod(methodName, param1.class, param2.class, ..);
} catch (SecurityException e) { ... }
catch (NoSuchMethodException e) { ... }
参数标识您需要的非常具体的方法（如果有多个重载可用，如果方法没有参数，则只给methodName）。
然后通过调用
调用该方法try {
method.invoke(obj, arg1, arg2,...);
} catch (IllegalArgumentException e) { ... }
catch (IllegalAccessException e) { ... }
catch (InvocationTargetException e) { ... }
再次，如果你没有参数，请忽略.invoke中的参数。但是，是的。阅读Java Reflection
答案 1 :(得分：177)
使用反射中的method invocation：
Class<?> c = Class.forName("class name");
Method method = c.getDeclaredMethod("method name", parameterTypes);
method.invoke(objectToInvokeOn, params);
其中：
"class name"是班级的名称objectToInvokeOn的类型为Object，是您要在"method name"是您要调用的方法的名称parameterTypes的类型为Class[]，并声明方法采用的参数params的类型为Object[]，并声明要传递给方法的参数答案 2 :(得分：81)
对于那些想要在Java 7中使用直接代码示例的人来说：
Dog课程：
package com.mypackage.bean;
public class Dog {
private String name;
private int age;
public Dog() {
// empty constructor
}
public Dog(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void printDog(String name, int age) {
System.out.println(name + " is " + age + " year(s) old.");
}
}
ReflectionDemo课程：
package com.mypackage.demo;
import java.lang.reflect.*;
public class ReflectionDemo {
public static void main(String[] args) throws Exception {
String dogClassName = "com.mypackage.bean.Dog";
Class<?> dogClass = Class.forName(dogClassName); // convert string classname to class
Object dog = dogClass.newInstance(); // invoke empty constructor
String methodName = "";
// with single parameter, return void
methodName = "setName";
Method setNameMethod = dog.getClass().getMethod(methodName, String.class);
setNameMethod.invoke(dog, "Mishka"); // pass arg
// without parameters, return string
methodName = "getName";
Method getNameMethod = dog.getClass().getMethod(methodName);
String name = (String) getNameMethod.invoke(dog); // explicit cast
// with multiple parameters
methodName = "printDog";
Class<?>[] paramTypes = {String.class, int.class};
Method printDogMethod = dog.getClass().getMethod(methodName, paramTypes);
printDogMethod.invoke(dog, name, 3); // pass args
}
}
<强>输出：
Mishka is 3 year(s) old.
您可以通过以下方式调用构造函数：
Constructor<?> dogConstructor = dogClass.getConstructor(String.class, int.class);
Object dog = dogConstructor.newInstance("Hachiko", 10);
或者，您可以删除
String dogClassName = "com.mypackage.bean.Dog";
Class<?> dogClass = Class.forName(dogClassName);
Object dog = dogClass.newInstance();
并做
Dog dog = new Dog();
Method method = Dog.class.getMethod(methodName, ...);
method.invoke(dog, ...);
答案 3 :(得分：54)
可以像这样调用该方法。还有更多的可能性（检查反射api），但这是最简单的一个：
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import org.junit.Assert;
import org.junit.Test;
public class ReflectionTest {
private String methodName = "length";
private String valueObject = "Some object";
@Test
public void testGetMethod() throws SecurityException, NoSuchMethodException, IllegalArgumentException,
IllegalAccessException, InvocationTargetException {
Method m = valueObject.getClass().getMethod(methodName, new Class[] {});
Object ret = m.invoke(valueObject, new Object[] {});
Assert.assertEquals(11, ret);
}
}
答案 4 :(得分：17)
首先，不要。避免使用这种代码。它往往是非常糟糕的代码和不安全的（参见Secure Coding Guidelines for the Java Programming Language, version 2.0的第6节）。
如果你必须这样做，那就选择java.beans来反思。豆类包裹反射，允许相对安全和传统的访问。
答案 5 :(得分：13)
要完成我同事的答案，您可能需要密切关注：
这是一个旧的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;
}
答案 6 :(得分：12)
//Step1 - Using string funClass to convert to class
String funClass = "package.myclass";
Class c = Class.forName(funClass);
//Step2 - instantiate an object of the class abov
Object o = c.newInstance();
//Prepare array of the arguments that your function accepts, lets say only one string here
Class[] paramTypes = new Class[1];
paramTypes[0]=String.class;
String methodName = "mymethod";
//Instantiate an object of type method that returns you method name
Method m = c.getDeclaredMethod(methodName, paramTypes);
//invoke method with actual params
m.invoke(o, "testparam");
答案 7 :(得分：11)
Object obj;
Method method = obj.getClass().getMethod("methodName", null);
method.invoke(obj, null);
答案 8 :(得分：11)
您可以使用FunctionalInterface将方法保存在容器中以对其进行索引。您可以使用数组容器通过数字调用它们，也可以使用哈希图通过字符串调用它们。通过此技巧，您可以索引方法以更快动态地调用它们。
@FunctionalInterface
public interface Method {
double execute(int number);
}
public class ShapeArea {
private final static double PI = 3.14;
private Method[] methods = {
this::square,
this::circle
};
private double square(int number) {
return number * number;
}
private double circle(int number) {
return PI * number * number;
}
public double run(int methodIndex, int number) {
return methods[methodIndex].execute(number);
}
}
您还可以使用lambda语法：
public class ShapeArea {
private final static double PI = 3.14;
private Method[] methods = {
number -> {
return number * number;
},
number -> {
return PI * number * number;
},
};
public double run(int methodIndex, int number) {
return methods[methodIndex].execute(number);
}
}
答案 9 :(得分：8)
如果多次执行调用，则可以使用Java 7中引入的新方法句柄。这里我们为您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]
答案 10 :(得分：7)
这听起来像Java Reflection包可以使用。
http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html
特别是按名称调用方法
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);
}
}
}
答案 11 :(得分：5)
请参考以下代码可能对您有帮助。
public static Method method[];
public static MethodClass obj;
public static String testMethod="A";
public static void main(String args[])
{
obj=new MethodClass();
method=obj.getClass().getMethods();
try
{
for(int i=0;i<method.length;i++)
{
String name=method[i].getName();
if(name==testMethod)
{
method[i].invoke(name,"Test Parameters of A");
}
}
}
catch(Exception ex)
{
System.out.println(ex.getMessage());
}
}
...谢谢
答案 12 :(得分：5)
我是这样做的：
try {
YourClass yourClass = new YourClass();
Method method = YourClass.class.getMethod("yourMethodName", ParameterOfThisMethod.class);
method.invoke(yourClass, parameter);
} catch (Exception e) {
e.printStackTrace();
}
答案 13 :(得分：5)
Method method = someVariable.class.getMethod(SomeClass);
String status = (String) method.invoke(method);
SomeClass是类，someVariable是变量。
答案 14 :(得分：3)
class Student{
int rollno;
String name;
void m1(int x,int y){
System.out.println("add is" +(x+y));
}
private void m3(String name){
this.name=name;
System.out.println("danger yappa:"+name);
}
void m4(){
System.out.println("This is m4");
}
}
import java.lang.reflect.Method;
public class StudentTest{
public static void main(String[] args){
try{
Class cls=Student.class;
Student s=(Student)cls.newInstance();
String x="kichha";
Method mm3=cls.getDeclaredMethod("m3",String.class);
mm3.setAccessible(true);
mm3.invoke(s,x);
Method mm1=cls.getDeclaredMethod("m1",int.class,int.class);
mm1.invoke(s,10,20);
}
catch(Exception e){
e.printStackTrace();
}
}
}
答案 15 :(得分：1)
这对我来说很好：
public class MethodInvokerClass {
public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, ClassNotFoundException, InvocationTargetException, InstantiationException {
Class c = Class.forName(MethodInvokerClass.class.getName());
Object o = c.newInstance();
Class[] paramTypes = new Class[1];
paramTypes[0]=String.class;
String methodName = "countWord";
Method m = c.getDeclaredMethod(methodName, paramTypes);
m.invoke(o, "testparam");
}
public void countWord(String input){
System.out.println("My input "+input);
}
}
输出：
My input testparam
我可以通过将其名称传递给另一个方法（如main）来调用该方法。
答案 16 :(得分：1)
使用import java.lang.reflect.*;
public static Object launchProcess(String className, String methodName, Class<?>[] argsTypes, Object[] methodArgs)
throws Exception {
Class<?> processClass = Class.forName(className); // convert string classname to class
Object process = processClass.newInstance(); // invoke empty constructor
Method aMethod = process.getClass().getMethod(methodName,argsTypes);
Object res = aMethod.invoke(process, methodArgs); // pass arg
return(res);
}
以下是您使用它的方式：
String className = "com.example.helloworld";
String methodName = "print";
Class<?>[] argsTypes = {String.class, String.class};
Object[] methArgs = { "hello", "world" };
launchProcess(className, methodName, argsTypes, methArgs);
答案 17 :(得分：1)
您应该使用反射 - 初始化类对象，然后使用此类中的方法，然后使用可选参数在对象上调用此方法。请记住将以下代码段包装在 try-catch 块
中希望它有所帮助！
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);
答案 18 :(得分：0)
以下是准备使用的方法：
要调用不带参数的方法：
public static void callMethodByName(Object object, String methodName) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
object.getClass().getDeclaredMethod(methodName).invoke(object);
}
使用参数调用方法：
public static void callMethodByName(Object object, String methodName, int i, String s) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
object.getClass().getDeclaredMethod(methodName, int.class, String.class).invoke(object, i, s);
}
使用以下方法：
package practice;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
public class MethodInvoke {
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, IOException {
String methodName1 = "methodA";
String methodName2 = "methodB";
MethodInvoke object = new MethodInvoke();
callMethodByName(object, methodName1);
callMethodByName(object, methodName2, 1, "Test");
}
public static void callMethodByName(Object object, String methodName) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
object.getClass().getDeclaredMethod(methodName).invoke(object);
}
public static void callMethodByName(Object object, String methodName, int i, String s) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
object.getClass().getDeclaredMethod(methodName, int.class, String.class).invoke(object, i, s);
}
void methodA() {
System.out.println("Method A");
}
void methodB(int i, String s) {
System.out.println("Method B: "+"\n\tParam1 - "+i+"\n\tParam 2 - "+s);
}
}
输出：
Method A Method B: Param1 - 1 Param 2 - Test
答案 19 :(得分：0)
使用jooR仅仅是：
on(obj).call(methodName /*params*/).get()
这是一个更详细的示例：
public class TestClass {
public int add(int a, int b) { return a + b; }
private int mul(int a, int b) { return a * b; }
static int sub(int a, int b) { return a - b; }
}
import static org.joor.Reflect.*;
public class JoorTest {
public static void main(String[] args) {
int add = on(new TestClass()).call("add", 1, 2).get(); // public
int mul = on(new TestClass()).call("mul", 3, 4).get(); // private
int sub = on(TestClass.class).call("sub", 6, 5).get(); // static
System.out.println(add + ", " + mul + ", " + sub);
}
}
此打印：
3，12，1
答案 20 :(得分：0)
对于那些从非静态方法调用同一类中的方法的人，请参阅以下代码：
class Person {
public void method1() {
try {
Method m2 = this.getClass().getDeclaredMethod("method2");
m1.invoke(this);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
public void method2() {
// Do something
}
}
答案 21 :(得分：-9)
public static object methodCaller(String methodName)
{
if(methodName.equals("getName"))
return className.getName();
}
然后当你需要调用方法时，只需输入类似的东西
//calling a toString method is unnessary here, but i use it to have my programs to both rigid and self-explanitory
System.out.println(methodCaller(methodName).toString());