功能接口，使用 Lambda 語法，可當作其他方法的傳入參數或是引用其他方法為實例，常用於循環訪問，傳入 2 個泛型物件參數，無傳回值，可以使用 andThen 組合成鏈式判斷，提高了程式碼的可管理性，有助於分別進行單元測試，BiConsumer Java Methods 介紹常見的 accept 、 andThen 等方法，了解 BiConsumer 的不同操作和方法，本篇增加了範例，並透過單元測試來驗證產出結果。
@FunctionalInterface
public interface BiConsumer<T, U> {
void accept(T t, U u);
}檔案目錄
單元測試
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- functional
| +- biconsumer
| +- BiConsumerMethodsTest.java BiConsumer Java Methods 提供 accept 、 andThen 條件或組合成鏈式判斷等操作 BiConsumer 。
accept
建立 BiConsumer 物件，傳入 2 個參數，執行程式邏輯。
@Test
public void accept() {
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
startsWith.accept("Bacon", "B");
startsWith.accept("Ham", "B");
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
lengthGreaterThan.accept("Bacon", 3);
lengthGreaterThan.accept("Ham", 3);
}true
false
true
falseandThen
BiConsumer Java Methods 建立 2 個 BiConsumer 物件，各傳入 2 個參數，使用 andThen 組合執行程式邏輯，並傳回 BiConsumer 繼續往下執行，其中若有例外拋出，將會中斷執行。
@Test
public void andThen() {
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
BiConsumer<String, String> endsWith = (s, s2) -> System.out.println(s.endsWith(s2));
startsWith.andThen(endsWith).accept("BaconB", "B");
startsWith.andThen(endsWith).accept("Ham", "B");
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
lengthGreaterThan.andThen(lengthMod).accept("BaconB", 5);
lengthGreaterThan.andThen(lengthMod).accept("Ham", 6);
}true
true
false
false
true
true
false
falsechaining
BiConsumer Methods in Java 建立多個 BiConsumer 物件，各傳入 2 個參數，使用 andThen 組合執行程式邏輯。
@Test
public void chaining() {
BiConsumer<String, String> contains = (s, s2) -> System.out.println(s.contains(s2));
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
BiConsumer<String, String> endsWith = (s, s2) -> System.out.println(s.endsWith(s2));
contains.andThen(startsWith).andThen(endsWith).accept("Bacon", "B");
contains.andThen(startsWith).andThen(endsWith).accept("Ham", "B");
BiConsumer<String, Integer> parseInt = (s, i) -> {
if (i < Integer.parseInt(s))
System.out.println(true);
System.out.println(false);
};
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
parseInt.andThen(lengthGreaterThan).andThen(lengthMod).accept("777", 2);
parseInt.andThen(lengthGreaterThan).andThen(lengthMod).accept("7", 2);
}true
true
false
false
false
false
true
false
true
true
true
false
false
true
traditional
BiConsumer Methods in Java 使用傳統方式，實作 BiConsumer 接口，執行程式邏輯。
@Test
public void traditional() {
BiConsumer<String, Integer> lengthGreaterThan = new LengthGreaterThan<String>();
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
lengthGreaterThan.andThen(lengthMod).accept("Bacon", 4);
lengthGreaterThan.andThen(lengthMod).accept("Ham", 3);
}true
true
false
falseBiConsumerMethodsTest.java
BiConsumer Methods in Java 新增單元測試，驗證 BiConsumer Functions in Java 是否符合預期。
package org.ruoxue.java_147.functional.biconsumer;
import java.util.function.BiConsumer;
import org.junit.Test;
public class BiConsumerMethodsTest {
@Test
public void accept() {
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
startsWith.accept("Bacon", "B");
startsWith.accept("Ham", "B");
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
lengthGreaterThan.accept("Bacon", 3);
lengthGreaterThan.accept("Ham", 3);
}
@Test
public void andThen() {
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
BiConsumer<String, String> endsWith = (s, s2) -> System.out.println(s.endsWith(s2));
startsWith.andThen(endsWith).accept("BaconB", "B");
startsWith.andThen(endsWith).accept("Ham", "B");
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
lengthGreaterThan.andThen(lengthMod).accept("BaconB", 5);
lengthGreaterThan.andThen(lengthMod).accept("Ham", 6);
}
@Test
public void chaining() {
BiConsumer<String, String> contains = (s, s2) -> System.out.println(s.contains(s2));
BiConsumer<String, String> startsWith = (s, s2) -> System.out.println(s.startsWith(s2));
BiConsumer<String, String> endsWith = (s, s2) -> System.out.println(s.endsWith(s2));
contains.andThen(startsWith).andThen(endsWith).accept("Bacon", "B");
contains.andThen(startsWith).andThen(endsWith).accept("Ham", "B");
BiConsumer<String, Integer> parseInt = (s, i) -> {
if (i < Integer.parseInt(s))
System.out.println(true);
System.out.println(false);
};
BiConsumer<String, Integer> lengthGreaterThan = (s, i) -> System.out.println(s.length() > i);
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
parseInt.andThen(lengthGreaterThan).andThen(lengthMod).accept("777", 2);
parseInt.andThen(lengthGreaterThan).andThen(lengthMod).accept("7", 2);
}
public static class LengthGreaterThan<E> implements BiConsumer<String, Integer> {
@Override
public void accept(String t, Integer u) {
System.out.println(t.length() > u);
}
}
@Test
public void traditional() {
BiConsumer<String, Integer> lengthGreaterThan = new LengthGreaterThan<String>();
BiConsumer<String, Integer> lengthMod = (s, i) -> System.out.println(s.length() % i == 1);
lengthGreaterThan.andThen(lengthMod).accept("Bacon", 4);
lengthGreaterThan.andThen(lengthMod).accept("Ham", 3);
}
}心得分享
BiConsumer Functions in Java 屬於 java.util.function ，常用於循環訪問，例如：迴圈內印出集合中的每個元素， 使用 Lambda 表達式能讓程式碼更加簡潔與直接，取代傳統實作接口的方法，減少了很多程式碼，大幅提高可讀性， BiConsumer Methods in Java 提供更清晰、更易讀且更靈活的方式來組合多個 BiConsumer 條件，來表示非常複雜的邏輯條件，如： accept 、 andThen 等，提供了幾種 BiConsumer 常見範例。
