将方法名称作为字符串给出时，如何调用Java方法？-Java 学习之路

606

如果我有两个变量：

Object obj;
String methodName = "getName";

在不知道 obj 类的情况下，如何调用 methodName 标识的方法呢？

被调用的方法没有参数，并且 String 返回值 . 它是Java bean的getter .

18 回答

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 .

回复于 2024-04-26T15:20:28+08:00

对于那些想要在Java 7中使用直接代码示例的人：

Dog class:

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 class:

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
    }
}

Output: Mishka is 3 year(s) old.

您可以通过以下方式调用带有参数的构造函数：

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, ...);

Suggested reading: Creating New Class Instances

回复于 2024-04-26T15:20:28+08:00

52

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（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，那就更喜欢java.beans来反思 . beans 包裹反射允许相对安全和传统的访问 .

回复于 2024-04-26T15:20:28+08:00

-9

Method method = someVariable.class.getMethod(SomeClass);
String status = (String) method.invoke(method);

SomeClass 是类， someVariable 是变量 .

回复于 2024-04-26T15:20:28+08:00

//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");

回复于 2024-04-26T15:20:28+08:00

Object obj;

Method method = obj.getClass().getMethod("methodName", null);

method.invoke(obj, null);

回复于 2024-04-26T15:20:28+08:00

9
从反射中使用method invocation：
```
Class<?> c = Class.forName("class name");
Method method = c.getDeclaredMethod("method name", parameterTypes);
method.invoke(objectToInvokeOn, params);
```
哪里：
- "class name" 是该类的名称
- objectToInvokeOn 是Object类型，是要调用方法的对象
- "method name" 是您要调用的方法的名称
- parameterTypes 的类型为 Class[] ，并声明方法所采用的参数
- params 的类型为 Object[] ，并声明要传递给方法的参数
回复于 2024-04-26T15:20:28+08:00

请参考以下代码可能对您有所帮助 .

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....

回复于 2024-04-26T15:20:28+08:00

169

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();
}

回复于 2024-04-26T15:20:28+08:00

从臀部编码，它将是这样的：

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（如果有多个可用的重载，如果方法没有参数，则只给出 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，请忽略 .invoke 中的参数 . 但是，是的 . 阅读Java Reflection

回复于 2024-04-26T15:20:28+08:00

这听起来像是Java Reflection包可以实现的 .

http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html

特别是 Invoking Methods by Name:

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);
     }
  }
}

回复于 2024-04-26T15:20:28+08:00

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String：

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]

回复于 2024-04-26T15:20:28+08:00

872
您应该使用反射 - 初始化类对象，然后使用此类中的方法，然后在具有可选参数的对象上调用此方法 . 请记住将以下代码段包装在try-catch块中

希望能帮助到你！
```
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);
```
回复于 2024-04-26T15:20:28+08:00

Student.java

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");
    }
}

StudentTest.java

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();
        }
     }
}

回复于 2024-04-26T15:20:28+08:00

对我来说，一个非常简单和简单的方法是简单地创建一个方法调用方法，如下所示：

public static object methodCaller(String methodName)
{
    if(methodName.equals("getName"))
        return className.getName();
}

那么当你需要调用方法时，只需要输入这样的东西

//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());

回复于 2024-04-26T15:20:28+08:00

为了完成我同事的答案，您可能需要密切关注：

静态或实例调用（在一种情况下，您不需要该类的实例，在另一种情况下，您可能需要依赖 existing default constructor ，可能存在也可能不存在）
公共或非公共方法调用（对于后者， you need to call setAccessible on the method within an doPrivileged block ，其他findbugs won't be happy）
如果要抛弃大量的java系统异常（因此下面的代码中的CCException），
封装成一个更易于管理的应用程序异常

这是一个旧的java1.4代码，它考虑了这些点：

/**
 * Allow for instance call, avoiding certain class circular dependencies. 

 * 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;
}

回复于 2024-04-26T15:20:28+08:00

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);
}

以下是你如何使用它：

String className = "com.example.helloworld";
String methodName = "print";
Class<?>[] argsTypes = {String.class,  String.class};
Object[] methArgs = { "hello", "world" };   
launchProcess(className, methodName, argsTypes, methArgs);

回复于 2024-04-26T15:20:28+08:00

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：

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);
    }



}

回复于 2024-04-26T15:20:28+08:00

将方法名称作为字符串给出时，如何调用Java方法？

18 回答

Student.java

StudentTest.java

相关问题