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 2 個同型別物件參數，執行完後會回傳同型別物件，使用 andThen 組合成鏈式判斷， Functional Interface BinaryOperator 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 BinaryOperator<T> extends BiFunction<T,T,T> {
public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) {
Objects.requireNonNull(comparator);
return (a, b) -> comparator.compare(a, b) <= 0 ? a : b;
}
public static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) {
Objects.requireNonNull(comparator);
return (a, b) -> comparator.compare(a, b) >= 0 ? a : b;
}
}檔案目錄
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- functional
| +- binaryoperator
| +- BinaryOperatorFunctionalTest.java
單元測試
BinaryOperator Functional Interface 提供方法引用、參考等操作 Java BinaryOperator Functional Interface 。
Food
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
BinaryOperator Functional Interface 建立一個 BinaryOperator ，引用其他方法為實例，執行程式邏輯，傳回物件。
@Test
public void methodReference() {
BinaryOperator<String> concat = String::concat;
String stringResult = concat.apply("Bacon", "Ham");
System.out.println(stringResult);
assertNotNull(stringResult);
BinaryOperator<Integer> max = Integer::max;
int intResult = max.apply(1, 10);
System.out.println(intResult);
assertEquals(10, intResult);
BinaryOperator<Boolean> equals = Objects::equals;
boolean booleanResult = equals.apply(Boolean.TRUE, Boolean.FALSE);
System.out.println(booleanResult);
assertFalse(booleanResult);
}BaconHam
10
falsemethodParameter
Functional Interface BinaryOperator in Java 建立一個 BinaryOperator ，當作其他方法的傳入參數，執行程式邏輯，傳回物件。
public static double calc(double d1, double d2, BinaryOperator<Double> binaryOperator) {
return binaryOperator.apply(d1, d2);
}
public static Food foodCalc(Food o1, Food o2, BinaryOperator<Food> binaryOperator) {
return binaryOperator.apply(o1, o2);
}
@Test
public void methodParameter() {
double result = calc(1d, 10d, (d1, d2) -> d1 + d2);
System.out.println(result);
assertEquals(11d, result, 2);
Food foodResult = foodCalc(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), (o1, o2) -> {
Food food = new Food("Pork", 3, 1);
food.setQuantity(o1.quantity + o2.quantity);
return food;
});
System.out.println(foodResult);
assertEquals(3d, foodResult.getQuantity(), 2);
}BaconHam
10
false
11.0
{"name":"Pork","quantity":3.0,"type":1}BinaryOperatorFunctionalTest.java
Functional Interface BinaryOperator in Java 新增單元測試，驗證 Java BinaryOperator Functional Interface 是否符合預期。
package org.ruoxue.java_147.functional.binaryoperator;
import static org.junit.Assert.*;
import java.util.Objects;
import java.util.function.BinaryOperator;
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 BinaryOperatorFunctionalTest {
@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() {
BinaryOperator<String> concat = String::concat;
String stringResult = concat.apply("Bacon", "Ham");
System.out.println(stringResult);
assertNotNull(stringResult);
BinaryOperator<Integer> max = Integer::max;
int intResult = max.apply(1, 10);
System.out.println(intResult);
assertEquals(10, intResult);
BinaryOperator<Boolean> equals = Objects::equals;
boolean booleanResult = equals.apply(Boolean.TRUE, Boolean.FALSE);
System.out.println(booleanResult);
assertFalse(booleanResult);
}
public static double calc(double d1, double d2, BinaryOperator<Double> binaryOperator) {
return binaryOperator.apply(d1, d2);
}
public static Food foodCalc(Food o1, Food o2, BinaryOperator<Food> binaryOperator) {
return binaryOperator.apply(o1, o2);
}
@Test
public void methodParameter() {
double result = calc(1d, 10d, (d1, d2) -> d1 + d2);
System.out.println(result);
assertEquals(11d, result, 2);
Food foodResult = foodCalc(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), (o1, o2) -> {
Food food = new Food("Pork", 3, 1);
food.setQuantity(o1.quantity + o2.quantity);
return food;
});
System.out.println(foodResult);
assertEquals(3d, foodResult.getQuantity(), 2);
}
}心得分享
Java BinaryOperator 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 BinaryOperator in Java 提供了幾種 BinaryOperator 常見方法的操作範例。
