Table of Contents
ToggleBiFunction in Java with Examples
只有一個抽象方法的接口,定義了 apply 方法,可以在一個元素上測試或應用一些操作,常用於物件轉換或數字運算,取代傳統實作接口的方法,讓程式碼更加簡潔和易讀, BiFunction in Java 本篇增加了範例,並透過單元測試來驗證產出結果。
@FunctionalInterface
public interface BiFunction<T, U, R> {
R apply(T t, U u);
}
檔案目錄
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- bifunctional
| +- bifunction
| +- BiFunctionWithExamplesTest.java
單元測試
BiFunction Java 提供 apply 、 andThen 條件或組合成鏈式判斷等操作 BiFunction 。
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();
}
}
apply
建立 BiFunction 物件,傳入 2 個參數,執行程式邏輯,傳回物件。
@Test
public void apply() {
BiFunction<Food, String, Boolean> startsWith = (o, s) -> o.name.startsWith(s);
Food food = new Food("Bacon", 1, 1);
boolean result = startsWith.apply(food, "B");
System.out.println(result);
assertTrue(result);
food = new Food("Ham", 3, 1);
result = startsWith.apply(food, "B");
System.out.println(result);
assertFalse(result);
BiFunction<Food, Integer, Boolean> greaterThan = (o, i) -> o.name.length() > i;
result = greaterThan.apply(new Food("Bacon", 1, 1), 3);
System.out.println(result);
assertTrue(result);
result = greaterThan.apply(new Food("Ham", 3, 1), 3);
System.out.println(result);
assertFalse(result);
}
true
false
true
false
andThen
BiFunction Java Methods 建立 1 個 BiFunction 物件,傳入 2 個參數,使用 andThen 組合執行程式邏輯,傳回物件,其中若有例外拋出,將會中斷執行。
@Test
public void andThen() {
BiFunction<Food, String, String> concat = (o, s) -> o.name.concat(s);
Function<String, Integer> multiply = s -> s.length() * 2;
Food food = new Food("Bacon", 1, 1);
int result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(12, result);
BiFunction<Food, Integer, Integer> length = (o, i) -> o.name.length() + i;
Function<Integer, Integer> twice = i -> i * i;
int intResult = length.andThen(twice).apply(new Food("Ham", 3, 1), 1);
System.out.println(intResult);
assertEquals(16, intResult);
}
12
16
andThenThrowException
BiFunction Java Methods 建立 BiFunction 物件,傳入參數 null ,會拋出例外 。
@Test(expected = NullPointerException.class)
public void andThenThrowException() {
BiFunction<Food, String, String> concat = (o, s) -> o.name.concat(s);
concat = concat.andThen(null);
}
java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.function.BiFunction.andThen(BiFunction.java:69)
at org.ruoxue.java_147.functional.bifunction.BiFunctionWithExamplesTest.andThenThrowException(BiFunctionWithExamplesTest.java:91)
traditional
BiFunction Methods in Java 使用傳統方式,實作 BiFunction 接口,傳回物件。
public static class Concat<E> implements BiFunction<Food, String, String> {
@Override
public String apply(Food t, String u) {
return t.name.concat(u);
}
}
@Test
public void traditional() {
BiFunction<Food, String, String> concat = new Concat<>();
Function<String, Integer> multiply = s -> s.length() * 2;
Food food = new Food("Bacon", 1, 1);
int result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(12, result);
food = new Food("Ham", 2, 1);
result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(8, result);
}
12
8
BiFunctionWithExamplesTest.java
BiFunction in Java 新增單元測試,驗證 Java BiFunction Example 是否符合預期。
package org.ruoxue.java_147.functional.bifunction;
import static org.junit.Assert.*;
import java.util.function.BiFunction;
import java.util.function.Function;
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 BiFunctionWithExamplesTest {
@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 apply() {
BiFunction<Food, String, Boolean> startsWith = (o, s) -> o.name.startsWith(s);
Food food = new Food("Bacon", 1, 1);
boolean result = startsWith.apply(food, "B");
System.out.println(result);
assertTrue(result);
food = new Food("Ham", 3, 1);
result = startsWith.apply(food, "B");
System.out.println(result);
assertFalse(result);
BiFunction<Food, Integer, Boolean> greaterThan = (o, i) -> o.name.length() > i;
result = greaterThan.apply(new Food("Bacon", 1, 1), 3);
System.out.println(result);
assertTrue(result);
result = greaterThan.apply(new Food("Ham", 3, 1), 3);
System.out.println(result);
assertFalse(result);
}
@Test
public void andThen() {
BiFunction<Food, String, String> concat = (o, s) -> o.name.concat(s);
Function<String, Integer> multiply = s -> s.length() * 2;
Food food = new Food("Bacon", 1, 1);
int result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(12, result);
BiFunction<Food, Integer, Integer> length = (o, i) -> o.name.length() + i;
Function<Integer, Integer> twice = i -> i * i;
int intResult = length.andThen(twice).apply(new Food("Ham", 3, 1), 1);
System.out.println(intResult);
assertEquals(16, intResult);
}
@Test(expected = NullPointerException.class)
public void andThenThrowException() {
BiFunction<Food, String, String> concat = (o, s) -> o.name.concat(s);
concat = concat.andThen(null);
}
public static class Concat<E> implements BiFunction<Food, String, String> {
@Override
public String apply(Food t, String u) {
return t.name.concat(u);
}
}
@Test
public void traditional() {
BiFunction<Food, String, String> concat = new Concat<>();
Function<String, Integer> multiply = s -> s.length() * 2;
Food food = new Food("Bacon", 1, 1);
int result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(12, result);
food = new Food("Ham", 2, 1);
result = concat.andThen(multiply).apply(food, "B");
System.out.println(result);
assertEquals(8, result);
}
}
心得分享
Java BiFunction Example 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, Java BiFunction 提供了幾種 BiFunction 常見方法的操作範例,例如: apply 、 andThen 等方法。