有没有办法在Java中按名称实例化一个类? [英] Is there a way to instantiate a class by name in Java?

问题描述

我在看问题:从字符串名称实例化一个类 描述了如何在拥有名称时实例化类.有没有办法在Java中做到这一点?我将获得包名和类名，并且我需要能够创建具有该特定名称的对象.

I was looking as the question : Instantiate a class from its string name which describes how to instantiate a class when having its name. Is there a way to do it in Java? I will have the package name and class name and I need to be able to create an object having that particular name.

推荐答案

两种方式:

如果您的类具有无参数构造函数，您可以使用 Class.forName() 获取 Class 对象并使用 newInstance()code> 方法来创建一个实例(但请注意，此方法通常被认为是邪恶的，因为它可以打败 Java 的检查异常).

If your class has a no-arg constructor, you can get a Class object using Class.forName() and use the newInstance() method to create an instance (though beware that this method is often considered evil because it can defeat Java's checked exceptions).

例如:

Class<?> clazz = Class.forName("java.util.Date");
Object date = clazz.newInstance();

方法二

如果类没有任何无参数构造函数，另一种更安全的方法也适用，即查询您的类对象以获取其 Constructor 对象并调用 newInstance() 此对象上的方法:

Method 2

An alternative safer approach which also works if the class doesn't have any no-arg constructors is to query your class object to get its Constructor object and call a newInstance() method on this object:

Class<?> clazz = Class.forName("com.foo.MyClass");
Constructor<?> constructor = clazz.getConstructor(String.class, Integer.class);
Object instance = constructor.newInstance("stringparam", 42);

这两种方法都被称为reflection.您通常必须捕获​​可能发生的各种异常，包括:

Both methods are known as reflection. You will typically have to catch the various exceptions which can occur, including things like:

• JVM 找不到或无法加载您的类
• 您尝试实例化的类没有正确类型的构造函数
• 构造函数本身抛出异常
• 您尝试调用的构造函数不是公开的
• 已安装安全管理器并防止发生反射

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