Table of Contents

Java Consumer Method Reference

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，例如引用 StringBuilder 、 List 、 Map 、 Queue 等， Consumer Method Reference Java 介紹常見的 append 、 add 、 remove 、 offer 等方法，了解 Consumer 的不同操作和應用，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
       |                       +- ConsumerWithExamplesTest.java

單元測試

Consumer Java Method Reference 提供方法引用、參考等操作 Consumer accept Java 。

StringBuilder_append

建立一個 Consumer ，使用 StringBuilder append ，新增字串。

	@Test
	public void StringBuilder_append() {
		StringBuilder value = new StringBuilder();
		Consumer<String> append = value::append;
		append.accept("Bacon, ");
		append.accept("Ham, ");
		append.accept("Pork");
		System.out.println(value);
	}

Bacon, Ham, Pork

List_add

Consumer Java Method Reference 建立一個 Consumer ，使用 List add ，增加三個元素。

	@Test
	public void List_add() {
		int expectedSize = 3;
		List<String> list = new ArrayList<String>();
		Consumer<String> add = list::add;
		add.accept("Bacon");
		add.accept("Ham");
		add.accept("Pork");
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

List_remove

[Bacon, Ham, Pork]

Consumer Java Method Reference 建立一個 Consumer ，使用 List remove ，內有三個元素，刪除指定元素。

	@Test
	public void List_remove() {
		int expectedSize = 2;
		List<String> list = new ArrayList<String>(Arrays.asList("Bacon", "Ham", "Pork"));
		Consumer<String> remove = list::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

[Ham, Pork]

Map_remove

Consumer Java Method Reference 建立一個 Consumer ，使用 Map remove ，內有三個元素，刪除指定元素。

	@Test
	public void Map_remove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Bacon", 1);
		map.put("Ham", 2);
		map.put("Pork", 3);
		Consumer<String> remove = map::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

{Ham=2, Pork=3}

Queue_offer

Java Consumer accept 建立一個 Consumer ，使用 Queue offer ，增加三個元素。

	@Test
	public void Queue_offer() {
		int expectedSize = 3;
		Queue<String> queue = new ConcurrentLinkedQueue<String>();
		Consumer<String> offer = queue::offer;
		offer.accept("Bacon");
		offer.accept("Ham");

		Consumer<String> queueOfferConsumer = queue::offer;
		queueOfferConsumer.accept("Pork");
		System.out.println(queue);
		assertEquals(expectedSize, queue.size());
	}

[Bacon, Ham, Pork]

Queue_remove

Java Consumer accept 建立一個 Consumer ，使用 Queue remove ，內有三個元素，刪除指定元素。

	@Test
	public void Queue_remove() {
		int expectedSize = 2;
		Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
		Consumer<String> remove = queue::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(queue);
		assertEquals(expectedSize, queue.size());
	}

[Ham, Pork]

ConsumerReferenceTest.java

Java Consumer accept 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.functional.consumer;

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.function.Consumer;

import org.junit.Test;

public class ConsumerReferenceTest {

	@Test
	public void StringBuilder_append() {
		StringBuilder value = new StringBuilder();
		Consumer<String> append = value::append;
		append.accept("Bacon, ");
		append.accept("Ham, ");
		append.accept("Pork");
		System.out.println(value);
	}

	@Test
	public void List_add() {
		int expectedSize = 3;
		List<String> list = new ArrayList<String>();
		Consumer<String> add = list::add;
		add.accept("Bacon");
		add.accept("Ham");
		add.accept("Pork");
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

	@Test
	public void List_remove() {
		int expectedSize = 2;
		List<String> list = new ArrayList<String>(Arrays.asList("Bacon", "Ham", "Pork"));
		Consumer<String> remove = list::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

	@Test
	public void Map_remove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Bacon", 1);
		map.put("Ham", 2);
		map.put("Pork", 3);
		Consumer<String> remove = map::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

	@Test
	public void Queue_offer() {
		int expectedSize = 3;
		Queue<String> queue = new ConcurrentLinkedQueue<String>();
		Consumer<String> offer = queue::offer;
		offer.accept("Bacon");
		offer.accept("Ham");

		Consumer<String> queueOfferConsumer = queue::offer;
		queueOfferConsumer.accept("Pork");
		System.out.println(queue);
		assertEquals(expectedSize, queue.size());
	}

	@Test
	public void Queue_remove() {
		int expectedSize = 2;
		Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
		Consumer<String> remove = queue::remove;
		remove.accept("Bacon");
		remove.accept("Bread");
		System.out.println(queue);
		assertEquals(expectedSize, queue.size());
	}
}