Constructor newInstance() method in Java with Examples

The newInstance() method of the java.lang.reflect.Constructor class is used to dynamically create objects at runtime by invoking a specific constructor through Java Reflection.

• Supports both no-argument and parameterized constructors
• Accepts constructor arguments dynamically
• Performs automatic unboxing for primitive parameters
• Returns a fully initialized object
• Commonly used in reflection-based frameworks for dynamic object creation

Object created

Explanation: The constructor is obtained using reflection and invoked using newInstance() to create a new object at runtime without using the new keyword.

Syntax:

constructor.newInstance(arguments);

Return Type:T - a new instance created by invoking the constructor

Example 1: Creating an Object Using a No-Argument Constructor

Output:

New Instance is created
New Instance

Explanation:

• Test.class.getConstructors(): retrieves all public constructors of the Test class.
• constructor[0].newInstance(): invokes the no-argument constructor reflectively, creating a new Test object and executing its constructor body, which initializes the value field and prints the message.

Example 2: Creating an Object Using a Parameterized Constructor

New Field

Explanation:

• The getConstructors() method retrieves all public constructors of the Test class at runtime.
• The first constructor is selected and invoked using newInstance("New Field"), passing a String argument dynamically.
• The parameterized constructor of Test initializes the field variable with the provided value.
• The getField() method is called on the created object to verify successful object creation and initialization.