How would I preform a selective deep copy in Java?

by

Summary

Performing a selective deep copy in Java can be challenging, especially when dealing with classes from external libraries that cannot be modified directly. The goal is to copy specific fields from one class to another without copying all fields. This can be achieved using reflection or other libraries that provide deep copying functionality with field filtering capabilities.

Root Cause

The root cause of the challenge is the inability to modify the external library class directly, combined with the need to selectively copy fields. This requires a approach that can inspect and manipulate the class fields at runtime.

Why This Happens in Real Systems

This issue occurs in real systems due to several reasons, including:

  • Reuse of third-party libraries: Classes from external libraries often cannot be modified.
  • Complex object graphs: Deep copying can be necessary to avoid unintended side effects.
  • Performance considerations: Copying only necessary fields can improve performance.

Real-World Impact

The impact of not being able to perform a selective deep copy can be significant, including:

  • Increased memory usage: Copying unnecessary fields can lead to memory waste.
  • Unintended side effects: Modifying the original object can have unforeseen consequences.
  • Performance degradation: Copying large objects can be slow.

Example or Code

import java.lang.reflect.Field;

public classSelectiveDeepCopy {
    public static void copyFields(Object source, Object target, String... fieldNames) throws IllegalAccessException {
        for (String fieldName : fieldNames) {
            Field sourceField = getField(source.getClass(), fieldName);
            Field targetField = getField(target.getClass(), fieldName);
            if (sourceField != null && targetField != null) {
                targetField.set(target, sourceField.get(source));
            }
        }
    }

    private static Field getField(Class clazz, String fieldName) {
        try {
            return clazz.getDeclaredField(fieldName);
        } catch (NoSuchFieldException e) {
            return null;
        }
    }
}

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Using reflection: To inspect and manipulate class fields at runtime.
  • Implementing custom deep copy logic: To selectively copy fields based on specific requirements.
  • Utilizing libraries: Such as Dozer or ModelMapper that provide deep copying functionality with field filtering capabilities.

Why Juniors Miss It

Juniors may miss this solution due to:

  • Lack of experience: With reflection and deep copying.
  • Insufficient knowledge: Of libraries that provide deep copying functionality.
  • Overlooking field filtering: Capabilities when using deep copying libraries.