Guava Collections2.transform() example

FunctionAsMember.java

private static Function<Entity, Integer> INVOKE_GET_ID =
	new Function<Entity, Integer>() {
		@Override
		public Integer apply(final Entity entity) {
			return entity.getId();
		}
	};

...

Collection<Integer> ids =
	Collections2.transform(entities, INVOKE_GET_ID);

TransformExample.java

import java.util.Arrays;
import java.util.Collection;
import com.google.common.base.Function;
import com.google.common.collect.Collections2;

class Entity {
	private final Integer id;
	
	public Entity(final Integer id) {
		this.id = id;
	}
	
	public Integer getId() {
		return id;
	}
	
}

public class GuavaTransform {
	
	public static void main(final String [] args) {
		
		Collection<Entity> entities = Arrays.asList(
			new Entity(1),
			new Entity(2),
			new Entity(3)
		);
		
		Collection<Integer> ids = Collections2.transform(
			entities,
			new Function<Entity, Integer>() {
				@Override
				public Integer apply(final Entity entity) {
					return entity.getId();
				}
			}
		);
		
		System.out.println(ids);
	}
	
}