Table of Contents

Consumer Functional Interface in Java

可當作其他方法的傳入參數或是引用其他方法為實例，使用 Lambda 語法，傳入 1 個泛型物件參數，無傳回值，使用 andThen 組合成鏈式判斷， Functional Interface Consumer 介紹常見的方法引用、方法參數等操作和方法，本篇增加了範例，並透過單元測試來驗證產出結果。

@FunctionalInterface
public interface Consumer<T> {
    void accept(T t);
}

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- functional
       |                   +- consumer
       |                       +- ConsumerFunctionalTest.java

單元測試

Consumer Functional Interface 提供方法引用、參考等操作 Java Consumer Functional Interface 。

Food

Consumer Functional Interface 建立 Food 類別，覆寫 equals 、 hashCode ，定義屬性和方法，用來建立一個物件。

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Food {
		private String name;
		private double quantity;
		private int type;

		public Food(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Food)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Food other = (Food) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

methodReference

Consumer Functional Interface 建立一個 Consumer ，引用其他方法為實例，循環訪問印出元素。

	@Test
	public void methodReference() {
		List<String> list = Arrays.asList("Bacon", "", "Ham", "Pork", "");
		Consumer<String> println = System.out::println;
		list.stream().forEach(println);

		List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), null, new Food("Ham", 2, 1),
				new Food("Pork", 3, 1), null);
		Consumer<Food> nonNull = o -> System.out.println(Objects.nonNull(o));
		Consumer<Food> contains = o -> {
			Optional<Food> opt = Optional.ofNullable(o);
			opt.ifPresent(e -> System.out.println(e.name.contains("o")));
		};
		foodList.stream().forEach(nonNull.andThen(contains));
	}

Bacon

Ham
Pork

true
true
false
true
false
true
true
false

methodParameter

Functional Interface Consumer in Java 建立一個 Consumer ，當作其他方法的傳入參數，循環訪問印出元素。

	public static void forEach(List<String> list, Consumer<String> consumer) {
		list.stream().forEach(consumer);
	}

	public static void foodForEach(List<Food> list, Consumer<Food> consumer) {
		list.stream().forEach(consumer);
	}

	@Test
	public void methodParameter() {
		List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
		Consumer<String> lengthGreaterThan = s -> System.out.println(s.length() > 3);
		forEach(list, lengthGreaterThan);

		List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
		Consumer<Food> lengthLessThan = o -> System.out.println(o.name.length() < 6);
		Consumer<Food> contains = o -> System.out.println(o.name.contains("o"));
		foodForEach(foodList, lengthLessThan.andThen(contains));
	}

Bacon

Ham
Pork

true
true
false
true
false
true
true
false

ConsumerFunctionalTest.java

Functional Interface Consumer in Java 新增單元測試，驗證 Java Consumer Functional Interface 是否符合預期。

package org.ruoxue.java_147.functional.consumer;

import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;

import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.junit.Test;

import lombok.Builder;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

public class ConsumerFunctionalTest {

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Food {
		private String name;
		private double quantity;
		private int type;

		public Food(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Food)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Food other = (Food) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

	@Test
	public void methodReference() {
		List<String> list = Arrays.asList("Bacon", "", "Ham", "Pork", "");
		Consumer<String> println = System.out::println;
		list.stream().forEach(println);

		List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), null, new Food("Ham", 2, 1),
				new Food("Pork", 3, 1), null);
		Consumer<Food> nonNull = o -> System.out.println(Objects.nonNull(o));
		Consumer<Food> contains = o -> {
			Optional<Food> opt = Optional.ofNullable(o);
			opt.ifPresent(e -> System.out.println(e.name.contains("o")));
		};
		foodList.stream().forEach(nonNull.andThen(contains));
	}

	public static void forEach(List<String> list, Consumer<String> consumer) {
		list.stream().forEach(consumer);
	}

	public static void foodForEach(List<Food> list, Consumer<Food> consumer) {
		list.stream().forEach(consumer);
	}

	@Test
	public void methodParameter() {
		List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
		Consumer<String> lengthGreaterThan = s -> System.out.println(s.length() > 3);
		forEach(list, lengthGreaterThan);

		List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
		Consumer<Food> lengthLessThan = o -> System.out.println(o.name.length() < 6);
		Consumer<Food> contains = o -> System.out.println(o.name.contains("o"));
		foodForEach(foodList, lengthLessThan.andThen(contains));
	}
}

心得分享

Java Consumer Functional Interface 除了傳統實作接口的方法，使用 Lambda 表達式實作功能，能讓程式碼更加簡潔與直接，大幅提高可讀性， Functional Interface Consumer in Java 提供了幾種 Consumer 常見方法的操作範例。