What is the difference between getDeclaredConstructors and getConstructors in the Java Class API?

What is the difference between getDeclaredConstructors and getConstructors in the Java Class API?

In Java, the getDeclaredConstructors and getConstructors methods are used to retrieve constructors from a class, but they differ in their accessibility and scope.

  1. getDeclaredConstructors:
    • The getDeclaredConstructors method is a part of the Java Reflection API, and it is used to retrieve all constructors of a class, including both public and non-public (private, protected, and package-private) constructors.
    • It returns an array of Constructor objects that represent all constructors declared within the class.
    • This method allows you to access constructors that are not normally accessible from outside the class, such as private constructors.

Here's an example of how to use getDeclaredConstructors:

import java.lang.reflect.Constructor; public class MyClass { private MyClass() { // Private constructor } public MyClass(int value) { // Public constructor } public static void main(String[] args) { Class<?> clazz = MyClass.class; Constructor<?>[] declaredConstructors = clazz.getDeclaredConstructors(); for (Constructor<?> constructor : declaredConstructors) { System.out.println("Constructor: " + constructor); } } }

In this example, getDeclaredConstructors retrieves both the private and public constructors of the MyClass class.

  1. getConstructors:
    • The getConstructors method is also part of the Reflection API, and it is used to retrieve only the public constructors of a class.
    • It returns an array of Constructor objects representing only the public constructors that are accessible from outside the class.
    • This method does not provide access to non-public constructors.

Here's an example of how to use getConstructors:

import java.lang.reflect.Constructor; public class MyClass { private MyClass() { // Private constructor } public MyClass(int value) { // Public constructor } public static void main(String[] args) { Class<?> clazz = MyClass.class; Constructor<?>[] constructors = clazz.getConstructors(); for (Constructor<?> constructor : constructors) { System.out.println("Constructor: " + constructor); } } }

In this example, getConstructors retrieves only the public constructor of the MyClass class.

To summarize, the main difference between getDeclaredConstructors and getConstructors is that getDeclaredConstructors retrieves all constructors of a class, including private and non-public ones, while getConstructors only retrieves the public constructors. The choice of which method to use depends on your specific use case and whether you need access to non-public constructors.

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