How to Create an Instance from a String in Java?

How do you instantiate an object from a String in Java?

// Example of converting a String representation of a class name to an instance
String className = "java.util.ArrayList";
Class<?> clazz = Class.forName(className);
List<?> instance = (List<?>) clazz.getDeclaredConstructor().newInstance();

In Java, you can create an object instance from the name of the class represented as a String using reflection. Reflection allows Java code to inspect classes, interfaces, fields, and methods at runtime, regardless of their visibility.

// Approach to create an instance using reflection
String className = "java.util.ArrayList";
try {
    Class<?> clazz = Class.forName(className);
    List<?> instance = (List<?>) clazz.getDeclaredConstructor().newInstance();
    System.out.println("Instance created: " + instance.getClass().getName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
    e.printStackTrace();
}

Causes

• Understanding of Java Reflection API
• Need for dynamic class instantiation at runtime
• Usage of class names stored as Strings

Solutions

• Import the required classes: `Class`, `List`, and any necessary exceptions.
• Use `Class.forName(className)` to get the Class object from the String.
• Create an instance using `newInstance()` or `getDeclaredConstructor().newInstance()`.

Mistake: Forgetting to handle exceptions properly when using reflection.

Solution: Always use try-catch blocks to handle potential exceptions.

Mistake: Assuming class names are in the same package without providing the full name.

Solution: Always include the full package name while referencing a class.