我想使用class . newinstance(),但我实例化的类没有null构造函数。因此,我需要能够传入构造函数参数。有办法做到这一点吗?


当前回答

按照以下步骤调用参数化构造函数。

通过在Class[]中传递类型获取带参数类型的构造函数 用于类的getDeclaredConstructor方法 通过在Object[]中传递值创建构造函数实例 构造函数的newInstance方法

示例代码:

import java.lang.reflect.*;

class NewInstanceWithReflection{
    public NewInstanceWithReflection(){
        System.out.println("Default constructor");
    }
    public NewInstanceWithReflection( String a){
        System.out.println("Constructor :String => "+a);
    }
    public static void main(String args[]) throws Exception {

        NewInstanceWithReflection object = (NewInstanceWithReflection)Class.forName("NewInstanceWithReflection").newInstance();
        Constructor constructor = NewInstanceWithReflection.class.getDeclaredConstructor( new Class[] {String.class});
        NewInstanceWithReflection object1 = (NewInstanceWithReflection)constructor.newInstance(new Object[]{"StackOverFlow"});

    }
}

输出:

java NewInstanceWithReflection
Default constructor
Constructor :String => StackOverFlow

其他回答

可以使用getConstructor(…)获取其他构造函数。

myObject.getClass().getDeclaredConstructors(types list).newInstance(args list);

编辑:根据评论似乎指向类和方法名是不够的一些用户。要了解更多信息,请参阅获取构造函数并调用它的文档。

MyClass.class.getDeclaredConstructor(String.class).newInstance("HERESMYARG");

or

obj.getClass().getDeclaredConstructor(String.class).newInstance("HERESMYARG");

你可以使用Class的getDeclaredConstructor方法。它需要一个类数组。下面是一个经过测试的工作示例:

public static JFrame createJFrame(Class c, String name, Component parentComponent)
{
    try
    {
        JFrame frame = (JFrame)c.getDeclaredConstructor(new Class[] {String.class}).newInstance("name");
        if (parentComponent != null)
        {
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }
        else
        {
            frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        }
        frame.setLocationRelativeTo(parentComponent);
        frame.pack();
        frame.setVisible(true);
    }
    catch (InstantiationException instantiationException)
    {
        ExceptionHandler.handleException(instantiationException, parentComponent, Language.messages.get(Language.InstantiationExceptionKey), c.getName());
    }
    catch(NoSuchMethodException noSuchMethodException)
    {
        //ExceptionHandler.handleException(noSuchMethodException, parentComponent, Language.NoSuchMethodExceptionKey, "NamedConstructor");
        ExceptionHandler.handleException(noSuchMethodException, parentComponent, Language.messages.get(Language.NoSuchMethodExceptionKey), "(Constructor or a JFrame method)");
    }
    catch (IllegalAccessException illegalAccessException)
    {
        ExceptionHandler.handleException(illegalAccessException, parentComponent, Language.messages.get(Language.IllegalAccessExceptionKey));
    }
    catch (InvocationTargetException invocationTargetException)
    {
        ExceptionHandler.handleException(invocationTargetException, parentComponent, Language.messages.get(Language.InvocationTargetExceptionKey));
    }
    finally
    {
        return null;
    }
}

假设您有以下构造函数

class MyClass {
    public MyClass(Long l, String s, int i) {

    }
}

你需要像这样表明你打算使用这个构造函数:

Class classToLoad = MyClass.class;

Class[] cArg = new Class[3]; //Our constructor has 3 arguments
cArg[0] = Long.class; //First argument is of *object* type Long
cArg[1] = String.class; //Second argument is of *object* type String
cArg[2] = int.class; //Third argument is of *primitive* type int

Long l = new Long(88);
String s = "text";
int i = 5;

classToLoad.getDeclaredConstructor(cArg).newInstance(l, s, i);