Getting Class Type From a String in Java
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Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:
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The Kubernetes ecosystem is huge and quite complex, so it’s easy to forget about costs when trying out all of the exciting tools.
To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.
Connect your cluster and start monitoring your K8s costs right away:
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1. Overview
The Class class plays a significant role in Java reflection, as it’s the entry point of all reflection operations.
In this quick tutorial, we’ll explore how to get the Class object from a class name in a string.
2. Introduction to the Problem
First of all, let’s create a simple class as an example:
package com.baeldung.getclassfromstr; public class MyNiceClass < public String greeting()< return "Hi there, I wish you all the best!"; >>As the code above shows, the MyNiceClass class is created in the package com.baeldung.getclassfromstr. Also, the class has only one method, greeting(), which returns a String.
Our goal is to get the Class object of the MyNiceClass class from its name. Further, we’d like to create a MyNiceClass‘s instance from the Class object to verify whether the Class object is the one we’re after.
For simplicity, we’ll use unit test assertions to verify if our solution works as expected.
Next, let’s see it in action.
3. Using the forName() Method to Get the Class Object
The Class class provides the forName() method to get the Class object from a class name as a string. Next, let’s see how to call the method to get the Class object of MyNiceClass:
Class cls = Class.forName("com.baeldung.getclassfromstr.MyNiceClass"); assertNotNull(cls);Next, let’s create a MyNiceClass instance from the Class object cls. If our Java version is older than 9, we can get an instance using the cls.newInstance() method. However, this method has been deprecated since Java 9. For the newer Java version, we can use cls.getDeclaredConstructor().newInstance() to obtain a new instance from the Class object:
MyNiceClass myNiceObject = (MyNiceClass) cls.getDeclaredConstructor().newInstance(); assertNotNull(myNiceObject); assertEquals("Hi there, I wish you all the best!", myNiceObject.greeting());The test passes when we give it a run. Therefore, we’ve got the desired Class object from the class name.
It’s worth mentioning that, to get the Class object, we must pass a qualified class name instead of a simple name to the forName() method. For example, we should pass the string “com.baeldung.getclassfromstr.MyNiceClass” to the forName() method. Otherwise, the forName() method throws ClassNotFoundException:
assertThrows(ClassNotFoundException.class, () -> Class.forName("MyNiceClass"));4. A Few Words About the Exception Handling
We’ve seen how to get MyNiceClass‘s Class object from its class name. For simplicity, we’ve omitted the exception handling in the test. Now, let’s look at which exceptions we should handle when we use the Class.forName() and the cls.getDeclaredConstructor().newInstance() methods.
First, Class.forName() throws ClassNotFoundException. We mentioned it when we passed MyNiceClass‘s simple name to it. ClassNotFoundException is a checked exception. Therefore, we must handle it when invoking the Class.forName() method.
Next, let’s look at cls.getDeclaredConstructor() and newInstance(). The getDeclaredConstructor() method throws NoSuchMethodException. Also, newInstance() throws InstantiationException, IllegalAccessException, IllegalArgumentException, and InvocationTargetException. All these five exceptions are checked exceptions. So, we need to handle them if we use these two methods.
It’s worth mentioning that all exceptions we’ve talked about in this section are subtypes of ReflectiveOperationException. That’s to say, if we don’t want to handle those exceptions individually, we can handle ReflectiveOperationException, for example:
void someNiceMethod() throws ReflectiveOperationException < Class cls = Class.forName("com.baeldung.getclassfromstr.MyNiceClass"); MyNiceClass myNiceObject = (MyNiceClass) cls.getDeclaredConstructor().newInstance(); // . >Or, we can use the try-catch block:
try < Class cls = Class.forName("com.baeldung.getclassfromstr.MyNiceClass"); MyNiceClass myNiceObject = (MyNiceClass) cls.getDeclaredConstructor().newInstance(); // . >catch (ReflectiveOperationException exception) < // handle the exception >5. Conclusion
In this short article, we’ve learned to use the Class.forName() method to obtain the Class object from a given class name string. We should note that we should pass the qualified name to the Class.forName() method.
As always, all code examples used in this article can be found over on GitHub.
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes: