Java method to assign object field values with Reflection

Question

I was wondering whether it would be possible to have something like the following in Java:

public class MyClass {
    private String name;
    private Integer age;
    private Date dateOfBirth;
    // constructors, getters, setters

    public void setField(String aFieldName, Object aValue) {
        Field aField = getClass().getDeclaredField(aFieldName);
        // use: aField.set(...) with proper type handling
    }
 }

I am really stuck in the setField method and any idea would be very helpful.

Thanks!

EDIT: The reason for this is that I would like to have a method in another class like the following

public static MyClass setAll(List<String> fieldNames, List<Object> fieldValues) {
    MyClass anObject = new MyClass();
    // iterate fieldNames and fieldValues and set for each fieldName 
    // the corresponding field value
    return anObject;
}

C. K. Young · Accepted Answer · 2011-09-22 06:46:01Z

7

Sure:

aField.set(this, aValue);

To do type checking first:

if (!aField.getType().isInstance(aValue))
    throw new IllegalArgumentException();

but since calling set with a value of the wrong type will generate an IllegalArgumentException anyway, that sort of check isn't very useful.

edited Sep 22, 2011 at 6:46

answered Sep 22, 2011 at 6:34

C. K. Young

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2 Comments

gpol Over a year ago

Yes I tried this but the thing is I would like to add some kind of type checking and appropriate casting in the method. Any ideas?

C. K. Young Over a year ago

You can do type checking if you want (but if all you do with a failed check is to throw, then that's pointless, since the reflection mechanism will throw for you). No casting will be appropriate.

Pål Brattberg · Accepted Answer · 2011-09-22 06:34:43Z

4

Though I'm at a loss as to why you would want to do it like that (since you already have getters and setters), try this:

Field aField = getClass().getDeclaredField(aFieldName);
aField.set(this, aValue);

For more info, see this.

answered Sep 22, 2011 at 6:34

Pål Brattberg

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2 Comments

gpol Over a year ago

Silly of me. I edited my question in order to explain why I want it.

Pål Brattberg Over a year ago

OK, is the answer good enough then? If you want to, you also have more specialized versions of set, such as setLong, setFloat, setBoolean etc. See the Javadoc referenced.

KV Prajapati · Accepted Answer · 2011-09-22 07:09:50Z

3

I'd like to suggest a map instead of List<T>.

 for(Map.Entry<String,Object> entry:map.entrySet())
  {
    Field aField = anObject.getClass().getDeclaredField(entry.getKey());
    if(entry.getValue().getClass().equals(aField.getType()))
         aField.set(anObject,entry.getValue());
  }
return anObject;

answered Sep 22, 2011 at 7:09

KV Prajapati

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