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

Java

import java.lang.reflect.Constructor;
class Test{
    public Test(){
        System.out.println("Object created");
    }
}
public class GFG {
    public static void main(String[] args) throws Exception {
        Constructor<Test> constructor = Test.class.getConstructor();
        constructor.newInstance();
    }
}

Output

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

Java

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class GFG{
    public static void main(String... args)
        throws InstantiationException,
               IllegalAccessException,
               IllegalArgumentException,
               InvocationTargetException
    {
        Constructor[] constructor= Test.class.getConstructors();
        Test sampleObject= (Test)constructor[0].newInstance();
        System.out.println(sampleObject.value);
    }
}

class Test {
    String value;
    public Test()
    {
        System.out.println("New Instance is created");
        value = "New Instance";
    }
}

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

Java

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class GFG{
    public static void main(String... args)
        throws InstantiationException,
               IllegalAccessException,
               IllegalArgumentException,
               InvocationTargetException
    {
        Constructor[] constructor= Test.class.getConstructors();
        Test sampleObject = (Test)constructor[0].newInstance("New Field");
        System.out.println(sampleObject.getField());
    }
}
class Test{
        private String field;

    public Test(String field)
    {
        this.field = field;
    }
    public String getField()
    {
        return field;
    }
    public void setField(String field)
    {
        this.field = field;
    }
}

Output

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.

Constructor newInstance() method in Java with Examples

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