Java - comparision fields using reflection

Question

I need compare all fields of two objects and return number of differences.

Pseudocode looks like below:

public int differentFields(Foo foo1, Foo foo2) {
    int differentFields = 0;
   for all fields of foo1 and foo2:
       if foo1.field[i] != foo2.field[i]
           differentFields++;

   return differentFields;
}

Fields have the same names because I want to compare objects of the same class.

I cannot do that using standard equals because Foo has a lot of fields and I would have to write too much if statements.

How can I do that using reflection?

Answer 1

As mentioned in the comments, it is a bad idea to use reflection to get all class members. This should solve your requirement:

public <T> int countDiff(T t1, T t2) throws Exception {
    int diffCount = 0;
    Class<? extends Object> tClass = t1.getClass();
    for (Field field : tClass.getDeclaredFields()) {
        field.setAccessible(true);
        Object value1 = field.get(t1);
        Object value2 = field.get(t2);
        if (!isEqual(value1, value2)) {
            diffCount++;
        }
    }
    return diffCount;
}

private boolean isEqual(Object v1, Object v2) {
    return (v1 == null && v2 == null) || (v1 != null && v1.equals(v2));
}

A quiet better solution would be to loop over the getter (but it is still a bad idea:

public <T> int countDiff(T t1, T t2) throws Exception {
    int diffCount = 0;
    Class<? extends Object> tClass = t1.getClass();
    for (Method method : tClass.getMethods()) {
        if (!isGetter(method)) {
            continue;
        }
        Object value1 = method.invoke(t1);
        Object value2 = method.invoke(t2);
        if (!isEqual(value1, value2)) {
            diffCount++;
        }
    }
    return diffCount;
}

private boolean isGetter(Method m) {
    boolean name = m.getName().startsWith("get") || m.getName().startsWith("is");
    return name && m.getParameterTypes().length == 0 && m.getReturnType() != Void.TYPE;
}

private boolean isEqual(Object v1, Object v2) {
    return (v1 == null && v2 == null) || (v1 != null && v1.equals(v2));
}

EDIT Thanks @tobias_k: also is methods for boolean added