Java中的参数类型

Question

我正在查看JasperReports的文档，但不理解以下方法的返回类型：

public java.lang.Class<?> getValueClass()

Answer 1

The method returns a Class object. The ? indicates that it can be any type of class. You can read more about wildcards here . These Class objects are often utilized when you're dealing with reflection .

Answer 2

Class<?> refers to any instance of Class. As compared to Class<? extends Collection> Class<? extends Collection> which would narrow the criteria down to a limited group of classes (those that extend Collection ).

This is particularly important when calling methods like newInstance . If you have Class<?> a and call a.newInstance() you'll get an Object . if you have Class<? extends Collection> Class<? extends Collection> and call b.newInstance() you'll get an instance of Collection .

Answer 3

It just returns an instance of a class. ? parameter which represents a generic wild card object ie it is a class of any type.