How to get a list of specific fields values from objects stored in a list?

Question

Say I have an list of objects with two fields field1 and field2, both of String type.

How do I get a list of all field1 values wit

Answer 1

Fortunately, you can do this using Java 8 - Streams

Assume you have an entity named YourEntity

public class YourEntity {

    private String field1;
    private String field2;

    public YourEntity(String field1, String field2) {
        this.field1 = field1;
        this.field2 = field2;
    }

    public void setField1(String field1) {
        this.field1 = field1;
    }

    public void setField2(String field2) {
        this.field2 = field2;
    }

    public String getField1() {
        return field1;
    }

    public String getField2() {
        return field2;
    }
}

Declare you list of YourEntity using:

List entities = Arrays.asList(new YourEntity("text1", "text2"), new YourEntity("text3", "text4"));

You can extract the list of field1 in one shot in this way:

import java.util.stream.Collectors;

List field1List = entities.stream().map(YourEntity::getField1).collect(Collectors.toList());

Or in this way

import java.util.stream.Collectors;

List field1List = entities.stream().map(urEntity -> urEntity.getField1()).collect(Collectors.toList());

You can print all the items also using java 8 :)

field1List.forEach(System.out::println);

Output

text1
text3