Description

how to get methods of a class in java ?

### How to Get Methods of a Class in Java

In Java, it is often necessary to programmatically retrieve the methods of a class for various purposes, such as introspection, debugging, or automation. Java provides a robust framework for doing so through Reflection. This article will guide you on how to get all methods of a class, including both public and non-public (private, protected, default) methods.

#### Understanding Reflection in Java
Java Reflection is a powerful feature that allows for introspection and manipulation of classes, methods, and fields at runtime. This means you can inspect and manipulate the structure and behavior of your programs dynamically. Reflection is accessible via the `java.lang.reflect` package.

#### Using `getMethods()`
The `java.lang.Class.getMethods()` method is used to retrieve all public methods (including inherited ones) from a class. This method returns an array of `Method` objects.

**Example**:
“`java
import java.lang.reflect.Method;

public class DumpMethods {
public void foo() {}
public void bar() {}
void baz() {}

public static void main(String[] args) {
try {
Method[] methods = DumpMethods.class.getMethods();
for (Method method : methods) {
System.out.println(method.getName());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
“`
When you run this code, it will print all public methods, including those inherited from `Object` class. If you replace `DumpMethods.class.getMethods()` with `java.util.List.class.getMethods()`, it will list all public methods of `List`.

#### Accessing Non-Public Methods
To get methods that are non-public (private, protected, default), you need to use `getDeclaredMethods()`. This method returns an array of `Method` objects reflecting all the methods declared by the class or interface, including public, private, protected, and default methods, but not inherited ones.

**Example**:
“`java
import java.lang.reflect.Method;

public class DumpMethods {
public void foo() {}
public void bar() {}
void baz() {} // Default access level

public static void main(String[] args) {
try {
Method[] methods = DumpMethods.class.getDeclaredMethods();
for (Method method : methods) {
System.out.println(method.getName());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
“`

This will list all methods declared by the `DumpMethods` class, including `foo`, `bar`, and `baz`.

#### Using `GetObject().getClass()`
The `getClass()` method of `Object` class can be used to get the runtime class of an object. This allows you to then use `getMethods()` or `getDeclaredMethods()` to inspect the methods of that object’s class.

**Example**:
“`java
import java.lang.reflect.Method;

public class DumpMethods {
public void foo() {}
public void bar() {}

public static void main(String[] args) {
DumpMethods obj = new DumpMethods();
try {
Method[] methods = obj.getClass().getDeclaredMethods();
for (Method method : methods) {
System.out.println(method.getName());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
“`

#### Additional Methods
– **getClasses()**: Retrieves all public member classes and interfaces that are declared by the class or interface represented by this `Class` object.
– **getMethod( String name, Class… parameterTypes )**: Retrieves a `public` method with the specified name and parameter types by introspection.
– **getDeclaredMethod( String name, Class… parameterTypes )**: Retrieves a method with the specified name and parameter types by introspection, including inherited methods.

#### Conclusion
Java provides several ways to get methods from a class using Reflection. By choosing the right method (`getMethods`, `getDeclaredMethods`, `getMethod`, or `getDeclaredMethod`), you can delve into a class’s structure and manipulate or invoke methods as needed. This can be particularly useful in scenarios where classes are being dynamically loaded or when you need to create flexible and extendible applications.

For further learning and examples, you can refer to the following resources:
– [Stack Overflow – How to get all methods of a class](https://stackoverflow.com/questions/5266532/can-i-get-all-methods-of-a-class)
– [GeeksforGeeks – getMethods()](https://www.geeksforgeeks.org/class-getmethods-method-in-java-with-examples/)
– [GeeksforGeeks – getMethod()](https://www.geeksforgeeks.org/class-getmethod-method-in-java-with-examples/)
– [Javatpoint – getClass()](https://www.javatpoint.com/java-object-getclass-method)
– [Tutorialspoint – List methods of a class using Java Reflection](https://www.tutorialspoint.com/list-methods-of-a-class-using-java-reflection)
– [YouTube Video Tutorial](https://www.google.com/sorry/index?continue=https%3A%2F%2Fwww.youtube.com%2Fresults%3Fsearch_query%3Dhow%2520to%2520get%2520methods%2520of%2520a%2520class%2520in%2520java) (note: directly follow the provided link)

By harnessing the power of Java’s Reflection, you can dive deeper into class structures, providing you with the flexibility and control to tackle complex programming tasks more efficiently.

If you’ve worked with Java Reflection before or have specific scenarios in mind, feel free to share them in the comments!