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 without having to iterate over the list, if it is at all possible?

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<YourEntity> 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<String> field1List = entities.stream().map(YourEntity::getField1).collect(Collectors.toList()); 

Or in this way

import java.util.stream.Collectors;  List<String> 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 

Answer 2

try this:

List<Entity> entities = getEntities(); List<Integer> listIntegerEntities = Lambda.extract(entities, Lambda.on(Entity.class).getFielf1()); 

the LambdaJ allows to access collections without explicit loops, so instead of have more lines of code to iterate the list yourself, you let LambdaJ do it.