从类对象实例化类 [英] instantiate class from class object

问题描述

在Java中，我可以使用类对象动态实例化该类型的类吗?

In java, can I use a class object to dynamically instantiate classes of that type?

即我想要这样的功能.

Object foo(Class type) {
    // return new object of type 'type'
}

推荐答案

在Java 9及更高版本中，如果存在声明的零参数(空")构造函数，则应使用

In Java 9 and afterward, if there's a declared zero-parameter ("nullary") constructor, you'd use Class.getDeclaredConstructor() to get it, then call newInstance() on it:

Object foo(Class type) throws InstantiationException, IllegalAccessException, InvocationTargetException {
    return type.getDeclaredConstructor().newInstance();
}

在Java 9之前，您应该使用

Prior to Java 9, you would have used Class.newInstance:

Object foo(Class type) throws InstantiationException, IllegalAccessException {
    return type.newInstance();
}

...但是从Java 9开始不推荐使用，因为它抛出了构造函数抛出的任何异常，甚至是检查过的异常，但是(当然)没有声明这些检查过的异常，从而有效地绕过了编译时检查过的异常处理. Constructor.newInstance将来自构造函数的异常包装在InvocationTargetException中.

...but it was deprecated as of Java 9 because it threw any exception thrown by the constructor, even checked exceptions, but didn't (of course) declare those checked exceptions, effectively bypassing compile-time checked exception handling. Constructor.newInstance wraps exceptions from the constructor in InvocationTargetException instead.

以上两种方法都假设有一个零参数构造函数.一种更可靠的方法是通过

Both of the above assume there's a zero-parameter constructor. A more robust route is to go through Class.getDeclaredConstructors or Class.getConstructors, which takes you into using the Reflection stuff in the java.lang.reflect package, to find a constructor with the parameter types matching the arguments you intend to give it.

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