CODEWITHSUNDEEP
javaandroidreflection
Jamling Li
Jamling Li

Reputation: 57

Android getDeclaredFields() return a disorder result

I declared a class like this:

public class Student implements Serializable {

    private static final long serialVersionUID = 8010508999597447226L;

    public long id;
    public String name;
    public int age;
    public String phone;
    public String address;

    public static void main(String[] args) {
        Field[] fields = Student.class.getFields();
        System.out.println("getFields(): " + fields2String(fields));
        fields = Student.class.getDeclaredFields();
        System.out.println("getDeclaredFields(): " + fields2String(fields));
    }

    private static String fields2String(Field[] fields) {
        if (fields != null) {
            StringBuilder sb = new StringBuilder();
            for (Field f : fields) {
                sb.append(f.getName());
                sb.append(",");
            }
            return sb.toString();
        }
        return null;
    }
}

The main running result is: (the order is same to my Student.java, my expected order)

getFields(): id,name,age,phone,address,
getDeclaredFields(): serialVersionUID,id,name,age,phone,address,

But the same code running on Android (4.1.2 Dalvik JVM), the result fields order is:

07-28 09:54:14.271 5972-5972/com.ex I/System.out: getFields(): address,age,id,name,phone,
07-28 09:54:14.271 5972-5972/com.ex I/System.out: getDeclaredFields(): serialVersionUID,address,phone,name,age,id,

The order is strange, not class order or alphabet order I noted that the implementation of getDelclaredFields() in Android is changed (it's native method public native Field[] getDeclaredFields();). It may be impossible to change the behavior. But I still want to known that how to get the ordered fields result.

Upvotes: 0

Views: 1113

Answers (1)

Totò
Totò

Reputation: 1854

If you need them in a particular order you can use Arrays.sort(). In the example below you would get them sorted by name (note that I'm using a lambda as the comparator):

Arrays.sort(getClass().getDeclaredFields(), (a, b) -> a.getName().compareTo(b.getName()));

Upvotes: 1

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