Why Is Reflection So Much Slower Than new? Java Object Creation Benchmarks

1. Basic Concepts

In Java, objects are usually created with the new operator, but they can also be instantiated via reflection.

The article asks when to use each method and compares their performance.

// new way
ReflectDemo reflectDemo = new ReflectDemo();

// reflection ways
Class<ReflectDemo> reflectDemoClass = ReflectDemo.class;
Class<?> aClass = Class.forName("com.whale.springtransaction.transactiondemo.reflectdemo.ReflectDemo");
Class<? extends Class> aClass = reflectDemoClass.getClass();

2. Performance Comparison

public class ReflectDemo {
    public static void main(String[] args) throws IllegalAccessException, InstantiationException {
        proxyObject();
        newObject();
    }

    // new object
    public static void newObject() {
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < 100000000; i++) {
            ReflectDemo reflectDemo = new ReflectDemo();
        }
        long endTime = System.currentTimeMillis();
        System.out.println("new耗时为:" + (endTime - startTime));
    }

    // reflection object
    public static void proxyObject() throws IllegalAccessException, InstantiationException {
        long startTime = System.currentTimeMillis();
        Class<ReflectDemo> reflectDemoClass = ReflectDemo.class;
        for (int i = 0; i < 100000000; i++) {
            ReflectDemo reflectDemo = reflectDemoClass.newInstance();
        }
        long endTime = System.currentTimeMillis();
        System.out.println("反射耗时为:" + (endTime - startTime));
    }
}

The test shows that creating 100 000 000 objects with new is many times faster than using reflection.

Reasons include:

Method#invoke performs argument boxing/unboxing.

Reflection requires accessibility checks.

Reflective calls cannot be inlined.

JIT cannot optimize reflective calls.

3. When to Use Reflection vs new

Reflection use cases:
1. Spring uses reflection to instantiate beans and put them into the IoC container.
2. Loading JDBC drivers with Class.forName().
3. Reverse engineering, e.g., decompilation.
4. Using reflection to store a String in an ArrayList<int>.

// Differences between new and reflection
1. Objects created with new cannot access private members; reflection can bypass access checks with setAccessible().
2. new requires the class name at compile time; reflection can instantiate without knowing the type at compile time.