引用其他方法為實例，使用 Lambda 語法，傳入 2 個泛型物件參數，執行完後會回傳 boolean 值，例如引用 Objects 、 String 、 List 、 Map 、 Queue 等， BiPredicate Method Reference Java 介紹常見的 equals 、 add 、 offer 、 contains 、 remove 等方法，了解 BiPredicate 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 BiPredicate<T> {
boolean test(T t, U u);
}
檔案目錄
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- functional
| +- bipredicate
| +- BiPredicateReferenceTest.java 單元測試
BiPredicate Java Method Reference 提供方法引用、參考等操作 BiPredicate test Java 。
Objects_equals
建立一個 BiPredicate ，使用 Objects equals ，檢查 2 個物件是否相等。
@Test
public void Objects_equals() {
BiPredicate<String, String> equals = Objects::equals;
boolean result = equals.test("Bacon", "Bacon");
System.out.println(result);
assertTrue(result);
result = equals.test("Bacon", null);
System.out.println(result);
assertFalse(result);
}true
falseString_contains
建立一個 BiPredicate ，使用 String contains ，檢查包含指定的字元。
@Test
public void String_contains() {
String value = "Bacon";
BiPredicate<String, String> contains = String::contains;
boolean result = contains.test(value, "o");
System.out.println(result);
assertTrue(result);
value = "Ham";
result = contains.test(value, "o");
System.out.println(result);
assertFalse(result);
}true
falseList_add
BiPredicate Java Method Reference 建立一個 BiPredicate ，使用 List add ，增加三個元素。
@Test
public void List_add() {
List<String> list = new ArrayList<String>();
BiPredicate<List<String>, String> add = List::add;
boolean result = add.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = add.test(list, "Ham");
System.out.println(result);
assertTrue(result);
result = add.test(list, "Pork");
System.out.println(result);
assertTrue(result);
System.out.println(list);
}true
true
true
[Bacon, Ham, Pork]List_remove
BiPredicate Java Method Reference 建立一個 BiPredicate ，使用 List remove ，內有三個元素，刪除指定元素。
@Test
public void List_remove() {
List<String> list = new ArrayList<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<List<String>, String> remove = List::remove;
boolean result = remove.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = remove.test(list, "Bread");
System.out.println(result);
assertFalse(result);
System.out.println(list);
}true
false
[Ham, Pork]List_contains
BiPredicate Java Method Reference 建立一個 BiPredicate ，使用 List contains ，內有三個元素，檢查包含指定的元素。
@Test
public void List_contains() {
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
BiPredicate<List<String>, String> contains = List::contains;
boolean result = contains.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = contains.test(list, "Bread");
System.out.println(result);
assertFalse(result);
}true
falseMap_containsKey
BiPredicate Java Method Reference 建立一個 BiPredicate ，使用 Map containsKey ，內有三個元素，檢查包含指定的 Key 。
@Test
public void Map_containsKey() {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Bacon", 1);
map.put("Ham", 2);
map.put("Pork", 3);
BiPredicate<Map<String, Integer>, String> containsKey = Map::containsKey;
boolean result = containsKey.test(map, "Bacon");
System.out.println(result);
assertTrue(result);
result = containsKey.test(map, "Bread");
System.out.println(result);
assertFalse(result);
}true
falseMap_containsValue
Java BiPredicate test 建立一個 BiPredicate ，使用 Map containsValue ，內有三個元素，檢查包含指定的 Value 。
@Test
public void Map_containsValue() {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Bacon", 1);
map.put("Ham", 2);
map.put("Pork", 3);
BiPredicate<Map<String, Integer>, Integer> containsValue = Map::containsValue;
boolean result = containsValue.test(map, 1);
System.out.println(result);
assertTrue(result);
result = containsValue.test(map, 9);
System.out.println(result);
assertFalse(result);
}true
falseQueue_offer
Java BiPredicate test 建立一個 BiPredicate ，使用 Queue offer ，增加三個元素。
@Test
public void Queue_offer() {
Queue<String> queue = new ConcurrentLinkedQueue<String>();
BiPredicate<Queue<String>, String> offer = Queue::offer;
boolean result = offer.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = offer.test(queue, "Ham");
System.out.println(result);
assertTrue(result);
Predicate<String> queueOfferPredicate = queue::offer;
result = queueOfferPredicate.test("Pork");
System.out.println(result);
assertTrue(result);
System.out.println(queue);
}true
true
true
[Bacon, Ham, Pork]Queue_remove
Java BiPredicate test 建立一個 BiPredicate ，使用 Queue remove ，內有三個元素，刪除指定元素。
@Test
public void Queue_remove() {
Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<Queue<String>, String> remove = Queue::remove;
boolean result = remove.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = remove.test(queue, "Bread");
System.out.println(result);
assertFalse(result);
System.out.println(queue);
}true
false
[Ham, Pork]Queue_contains
Java BiPredicate test 建立一個 BiPredicate ，使用 Queue contains ，內有三個元素，檢查包含指定的元素。
@Test
public void Queue_contains() {
Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<Queue<String>, String> contains = Queue::contains;
boolean result = contains.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = contains.test(queue, "Bread");
System.out.println(result);
assertFalse(result);
}true
falseBiPredicateReferenceTest.java
Java BiPredicate test 新增單元測試，驗證是否符合預期。
package org.ruoxue.java_147.functional.bipredicate;
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.Objects;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.function.BiPredicate;
import java.util.function.Predicate;
import org.junit.Test;
public class BiPredicateReferenceTest {
@Test
public void Objects_equals() {
BiPredicate<String, String> equals = Objects::equals;
boolean result = equals.test("Bacon", "Bacon");
System.out.println(result);
assertTrue(result);
result = equals.test("Bacon", null);
System.out.println(result);
assertFalse(result);
}
@Test
public void String_contains() {
String value = "Bacon";
BiPredicate<String, String> contains = String::contains;
boolean result = contains.test(value, "o");
System.out.println(result);
assertTrue(result);
value = "Ham";
result = contains.test(value, "o");
System.out.println(result);
assertFalse(result);
}
@Test
public void List_add() {
List<String> list = new ArrayList<String>();
BiPredicate<List<String>, String> add = List::add;
boolean result = add.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = add.test(list, "Ham");
System.out.println(result);
assertTrue(result);
result = add.test(list, "Pork");
System.out.println(result);
assertTrue(result);
System.out.println(list);
}
@Test
public void List_remove() {
List<String> list = new ArrayList<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<List<String>, String> remove = List::remove;
boolean result = remove.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = remove.test(list, "Bread");
System.out.println(result);
assertFalse(result);
System.out.println(list);
}
@Test
public void List_contains() {
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
BiPredicate<List<String>, String> contains = List::contains;
boolean result = contains.test(list, "Bacon");
System.out.println(result);
assertTrue(result);
result = contains.test(list, "Bread");
System.out.println(result);
assertFalse(result);
}
@Test
public void Map_containsKey() {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Bacon", 1);
map.put("Ham", 2);
map.put("Pork", 3);
BiPredicate<Map<String, Integer>, String> containsKey = Map::containsKey;
boolean result = containsKey.test(map, "Bacon");
System.out.println(result);
assertTrue(result);
result = containsKey.test(map, "Bread");
System.out.println(result);
assertFalse(result);
}
@Test
public void Map_containsValue() {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Bacon", 1);
map.put("Ham", 2);
map.put("Pork", 3);
BiPredicate<Map<String, Integer>, Integer> containsValue = Map::containsValue;
boolean result = containsValue.test(map, 1);
System.out.println(result);
assertTrue(result);
result = containsValue.test(map, 9);
System.out.println(result);
assertFalse(result);
}
@Test
public void Queue_offer() {
Queue<String> queue = new ConcurrentLinkedQueue<String>();
BiPredicate<Queue<String>, String> offer = Queue::offer;
boolean result = offer.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = offer.test(queue, "Ham");
System.out.println(result);
assertTrue(result);
Predicate<String> queueOfferPredicate = queue::offer;
result = queueOfferPredicate.test("Pork");
System.out.println(result);
assertTrue(result);
System.out.println(queue);
}
@Test
public void Queue_remove() {
Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<Queue<String>, String> remove = Queue::remove;
boolean result = remove.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = remove.test(queue, "Bread");
System.out.println(result);
assertFalse(result);
System.out.println(queue);
}
@Test
public void Queue_contains() {
Queue<String> queue = new ConcurrentLinkedQueue<String>(Arrays.asList("Bacon", "Ham", "Pork"));
BiPredicate<Queue<String>, String> contains = Queue::contains;
boolean result = contains.test(queue, "Bacon");
System.out.println(result);
assertTrue(result);
result = contains.test(queue, "Bread");
System.out.println(result);
assertFalse(result);
}
}心得分享
BiPredicate test Java 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， Java BiPredicate test 提供了幾種 BiPredicate 常見方法的操作範例。
