Common calling methods in Java reflection

In Java programming, reflection is a method that can inspect, obtain and operate classes, interfaces, methods, Mechanism for fields and other information. Using reflection, we can dynamically call methods, create instances, obtain class information, etc. at runtime, providing greater flexibility and scalability for program design. This article will use specific code examples to demonstrate common calling methods in Java reflection to help readers gain an in-depth understanding of the application of reflection.

Get the Class object

Before using reflection, you first need to obtain the Class object of the corresponding class. You can get the Class object based on the fully qualified name of the class through the Class.forName() method, you can also get the Class object through the object's getClass() method, or you can use the class name directly. .class to obtain.

// 通过Class.forName()获取Class对象
Class<?> clazz1 = Class.forName("com.example.MyClass");

// 通过对象的getClass()方法获取Class对象
MyClass obj = new MyClass();
Class<?> clazz2 = obj.getClass();

// 直接使用类名.class获取Class对象
Class<?> clazz3 = MyClass.class;

Instancing objects

Through reflection, an object of a class can be dynamically created. After obtaining the Class object, you can use the newInstance() method to create an instance.

Class<?> clazz = Class.forName("com.example.MyClass");
MyClass obj = (MyClass) clazz.newInstance();

Calling methods

Using reflection, you can dynamically call methods in a class. Suppose there is a class MyClass, which contains a method public void doSomething(String param), which we can call through reflection.

// 获取Method对象
Class<?> clazz = Class.forName("com.example.MyClass");
Method method = clazz.getMethod("doSomething", String.class);

// 创建对象
MyClass obj = (MyClass) clazz.newInstance();

// 调用方法
method.invoke(obj, "Hello, Reflection!");

Getting and setting field values

Through reflection, you can get and set the values ​​of fields in a class. Suppose there is a class MyClass, which contains a field private String name. We can get and set the value of this field through reflection.

// 获取Field对象
Class<?> clazz = Class.forName("com.example.MyClass");
Field field = clazz.getDeclaredField("name");

// 创建对象
MyClass obj = (MyClass) clazz.newInstance();

// 设置字段的值
field.setAccessible(true);
field.set(obj, "Reflection");

// 获取字段的值
String name = (String) field.get(obj);

Application of Generic Types

When using reflection, sometimes it involves the processing of generic types. For example, if a method returns List<String>, we need to obtain the actual type of the return value through reflection.

Method method = SomeClass.class.getMethod("getList");
Type returnType = method.getGenericReturnType();
if (returnType instanceof ParameterizedType) {
    ParameterizedType type = (ParameterizedType) returnType;
    Type[] typeArguments = type.getActualTypeArguments();
    for (Type typeArgument : typeArguments) {
        Class<?> typeArgClass = (Class<?>) typeArgument;
        System.out.println("List的实际类型是：" + typeArgClass.getName());
    }
}

Summary

Through the above examples, we have demonstrated common calling methods in Java reflection, including obtaining Class objects, instantiating objects, calling methods, getting and setting field values, and handling generics . Reflection provides an effective way to obtain and manipulate class information at runtime, but due to the flexibility and dynamics of reflection, it may increase the complexity and performance overhead of the code, so you need to consider carefully when using reflection. I hope this article can help readers better understand and apply Java reflection.

Through the above examples, readers can have a deeper understanding of the application of reflection, and at the same time, they can also conduct more practice and exploration according to specific situations. Reflection, as an important feature in Java programming, can bring greater flexibility and scalability to program design, and has extensive application value in actual projects.

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