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

我的问题是：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一个类。有没有办法在Java中做到这一点？我将拥有包名和类名，我需要能够创建一个具有该特定名称的对象。

I was looking as the question : Instantiate an 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

两个方式：

如果您的类没有-arg构造函数，您可以使用 Class.forName（）获取 Class 对象并使用 newInstance（）创建实例的方法（虽然要注意这种方法通常是被认为是邪恶的，因为它可以击败Java的已检查异常）。

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2

另一种更安全的方法如果类没有任何no-arg构造函数，它也可以查询你的类对象以获取它的构造函数对象并调用 newInstance（ ）此对象的方法：

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);

这两种方法都称为反射。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无法找到或无法加载你的类


• 你试图实例化的类没有正确的构造函数


• 构造函数本身抛出异常


• 您尝试调用的构造函数不公开


• 已安装安全管理器并阻止反射发生

• the JVM can't find or can't load your class
• the class you're trying to instantiate doesn't have the right sort of constructors
• the constructor itself threw an exception
• the constructor you're trying to invoke isn't public
• a security manager has been installed and is preventing reflection from occurring

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