Java - map a list of objects to a list with values of their property attributes

Question

I have the ViewValue class defined as follows:

class ViewValue {

private Long id;
private Integer value;
private String description;
private View view;
priv         


        

Answer 1

Use google collections. Example:

    Function transform = new Function() {
        @Override
        public Long apply(ViewValue from) {
            return from.getId();
        }
    };
    List list = Lists.newArrayList();
    List idsList = Lists.transform(list, transform);

UPDATE:

On Java 8 you don't need Guava. You can:

import com.example.ViewValue;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;

Function transform = ViewValue::getId;
List source = new ArrayList<>();
List result = source.stream().map(transform).collect(Collectors.toList());

Or just:

List source= new ArrayList<>();
List result = source.stream().map(ViewValue::getId).collect(Collectors.toList());

NEXT UPDATE (The last one after Javaslang to Vavr name change):

Currently it's worth to mention about the solution with Javaslang library(http://www.javaslang.io/) Vavr library (http://www.vavr.io/). Let's assume that we have our list with genuine objects:

List source = newArrayList(new ViewValue(1), new ViewValue(2), new ViewValue(2));

We could make transformation with List class from Javaslang library (on the long run the collect is not convenient):

List result = io.vavr.collection.List.ofAll(source).map(ViewValue::getId).toJavaList();

But you will see the power with only the Javaslang lists:

io.vavr.collection.List source = javaslang.collection.List.of(new ViewValue(1), new ViewValue(2), new ViewValue(3));
io.vavr.collection.List res = source.map(ViewValue::getId);

I encourage to take a look available collections and new types on that library (I like especially the Try type). You will find the documentation under the following address: http://www.javaslang.io/javaslang-docs/ http://www.vavr.io/vavr-docs/.

PS. Due to the Oracle and the "Java" word within the name they had to change the library name from javaslang to something else. They had decided to Vavr.