Four ways to obtain Class objects through reflection

Java reflection mechanism

Reflection: Through reflection, we can get all the properties and methods of any class, and we can also call these methods and properties.

Advantages and disadvantages of reflection

Benefits: Makes the code more flexible and provides convenience for out-of-the-box functionality for various frameworks
Disadvantages: It gives us the ability to analyze operation classes at runtime, which also increases security issues.
For example, the security check of generic parameters can be ignored (the security check of generic parameters occurs at compile time).
In addition, the performance of reflection is also slightly worse, but it has little effect on the framework.

If we get this information dynamically, we need to rely on the Class object.Class class object tells the running program of a class's methods, variables and other information.

Four ways to get a Class object

• via Class.forName()Get the full path of the incoming class

• Get by instance.getClass() of the object instancestrong>

• Get the full path of the class through the class loader ClassLoader.loadClass()

• Get through a specific instance object

Give a chestnut

 /*** 4 ways to obtain Class objects through reflection*/@Testpublic void reflectGetMethod_Test() {try {String classPath = "com.hl.magic.items.day20.reflection.ReflectiveDemo";Class forName = Class.forName(classPath);LOGGER.debug("[1]Get the path of the current class according to the full path of the class: {}", forName.getName());String name = ReflectiveDemo.class.getName();LOGGER.debug("[2]-Get the path of the current class according to the class object: {}", name);ReflectiveDemo reflectiveDemo = new ReflectiveDemo();Class aClass = reflectiveDemo.getClass();LOGGER.debug("[3]Get the path of the current class according to the object instance: {}", aClass.getName());Class aClass1 = ClassLoader.getSystemClassLoader().loadClass(classPath);LOGGER.debug("[4]Get the path of the current class according to the class loader: {}", aClass1.getName());// Get the corresponding property according to the class pathReflectiveDemo reflectiveDemo1 = (ReflectiveDemo) forName.newInstance();String userName = reflectiveDemo1.getUserName();LOGGER.debug("Get the properties of the reflection object: [{}]", userName);} catch ( ClassNotFoundException | InstantiationException | IllegalAccessException e) {e.printStackTrace();}}

Output:

[main] DEBUG com.hl.magic.items.day20.reflection.ReflectiveDemo - [1] Get the path of the current class based on the full class path: com.hl.magic.items.day20.reflection.ReflectiveDemo[main] DEBUG com.hl.magic.items.day20.reflection.ReflectiveDemo - [2]-Get the path of the current class according to the class object: com.hl.magic.items.day20.reflection.ReflectiveDemo[main] DEBUG com.hl.magic.items.day20.reflection.ReflectiveDemo - [3] Get the path of the current class according to the object instance: com.hl.magic.items.day20.reflection.ReflectiveDemo[main] DEBUG com.hl.magic.items.day20.reflection.ReflectiveDemo - [4] Get the path of the current class according to the class loader: com.hl.magic.items.day20.reflection.ReflectiveDemo[main] DEBUG com.hl.magic.items.day20.reflection.ReflectiveDemo - Get the properties of the reflection object: [Xiao Ming]

Getting a Class object through the class loader will not be initialized, which means that static code blocks and static objects will not be executed without a series of steps including initialization.