Table of Contents
ToggleJava UnaryOperator Interface
常用於物件轉換或數字運算,也可當作其他方法的傳入參數或是引用其他方法為實例, UnaryOperator Interface 介紹 Optional 中的 map 與 Stream 中的 map 、 flatMap 等方法,了解 UnaryOperator 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 UnaryOperator<T> extends Function<T, T> {
static <T> UnaryOperator<T> identity() {
return t -> t;
}
}
檔案目錄
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- functional
| +- unaryoperator
| +- UnaryOperatorInterfaceTest.java
單元測試
UnaryOperator Interface Java 提供 Optional 中的 map 與 Stream 中的 map 、 flatMap 等方法操作 UnaryOperator Interface 。
Food
UnaryOperator Interface Java 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();
}
}
Optional_map
UnaryOperator Interface Java 建立 UnaryOperator ,建立 Optional 容器,轉換容器內的值,傳回 Optional。
@Test
public void Optional_map() {
Optional<String> opt = Optional.ofNullable("Bacon");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
Optional<String> toUpperCaseOpt = opt.map(toUpperCase);
String result = toUpperCaseOpt.orElse("");
System.out.println(result);
assertEquals("BACON", result);
Optional<Food> foodOpt = Optional.ofNullable(new Food("Ham", 1, 1));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Optional<Food> booleanOpt = foodOpt.map(addition.andThen(multiply));
Food foodResult = booleanOpt.orElse(null);
System.out.println(foodResult);
assertNotNull(foodResult);
}
BACON
{"name":"Ham","quantity":8.0,"type":1}
Stream_map
UnaryOperator Interface Java 建立 UnaryOperator ,建立 Optional 容器,轉換容器內的值,傳回 Optional 。
@Test
public void Stream_map() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
Stream<String> stream = list.stream().map(toUpperCase);
long count = stream.peek(System.out::println).count();
assertEquals(expectedSize, count);
List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Stream<Food> foodStream = foodList.stream().map(addition.andThen(multiply));
count = foodStream.peek(System.out::println).count();
assertEquals(expectedSize, count);
}
Optional[Optional[BACON]]
Optional[BACON]
Stream_flatMap
UnaryOperator Interface Java 建立 UnaryOperator ,建立 Stream ,轉換流內的值,傳回 Stream 。
@Test
public void Stream_flatMap() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> toUpperCase = String::toUpperCase;
List<String> result = list.stream().map(toUpperCase).collect(Collectors.toList());
System.out.println(result);
assertEquals(expectedSize, result.size());
List<List<String>> nestedlist = Arrays.asList(Arrays.asList("Bacon"), Arrays.asList("Ham"),
Arrays.asList("Pork"));
List<String> nestedResult = nestedlist.stream().flatMap(Collection::stream).collect(Collectors.toList());
System.out.println(nestedResult);
assertEquals(expectedSize, nestedResult.size());
}
[BACON, HAM, PORK]
[Bacon, Ham, Pork]
Map_computeIfAbsent
UnaryOperator Interface in Java 建立 UnaryOperator ,建立一個 HashMap ,內有三個元素,計算不存在的 Key 新值, Java UnaryOperator Interface Example 提供了範例參考。
@Test
public void Map_computeIfAbsent() {
Map<String, String> map = new HashMap<String, String>();
map.put("Bacon", "Bacon");
map.put("Ham", "Ham");
map.put("Pork", "Pork");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
String result = map.computeIfAbsent("Bread", toUpperCase);
System.out.println(map);
assertEquals("BREAD", result);
Map<Food, Food> foodMap = new HashMap<Food, Food>();
foodMap.put(new Food("Bacon", 1, 1), new Food("Bacon", 1, 1));
foodMap.put(new Food("Ham", 2, 1), new Food("Ham", 1, 2));
foodMap.put(new Food("Pork", 3, 1), new Food("Pork", 1, 3));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Food foodResult = foodMap.computeIfAbsent(new Food("Bread", 1, 1), addition.andThen(multiply));
System.out.println(foodMap);
assertEquals(8d, foodResult.getQuantity(), 2);
}
{Ham=Ham, Bacon=Bacon, Pork=Pork, Bread=BREAD}
{{"name":"Bacon","quantity":1.0,"type":1}={"name":"Bacon","quantity":1.0,"type":1}, {"name":"Ham","quantity":2.0,"type":1}={"name":"Ham","quantity":1.0,"type":2}, {"name":"Bread","quantity":8.0,"type":1}={"name":"Bread","quantity":8.0,"type":1}, {"name":"Pork","quantity":3.0,"type":1}={"name":"Pork","quantity":1.0,"type":3}}
Collectors_toMap
UnaryOperator Interface in Java 建立 UnaryOperator ,建立一個 List ,內有三個元素,轉換成 Map , Java UnaryOperator Interface Example 提供了範例參考。
@Test
public void Collectors_toMap() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> key = s -> s.toUpperCase();
UnaryOperator<String> toLowerCase = s -> s.toLowerCase();
Map<String, String> map = list.stream().collect(Collectors.toMap(key, toLowerCase));
System.out.println(map);
assertEquals(expectedSize, map.size());
List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
UnaryOperator<Food> foodKey = o -> o;
UnaryOperator<Food> half = o -> {
o.setQuantity(o.getQuantity() / 2);
return o;
};
UnaryOperator<Food> twice = o -> {
o.setQuantity(o.getQuantity() * o.getQuantity());
return o;
};
Map<Food, Food> foodMap = foodList.stream().collect(Collectors.toMap(foodKey, half.andThen(twice)));
System.out.println(foodMap);
assertEquals(expectedSize, foodMap.size());
}
{BACON=bacon, HAM=ham, PORK=pork}
{{"name":"Bacon","quantity":0.25,"type":1}={"name":"Bacon","quantity":0.25,"type":1}, {"name":"Ham","quantity":1.0,"type":1}={"name":"Ham","quantity":1.0,"type":1}, {"name":"Pork","quantity":2.25,"type":1}={"name":"Pork","quantity":2.25,"type":1}}
UnaryOperatorInterfaceTest.java
UnaryOperator Interface in Java 新增單元測試,驗證 Java UnaryOperator Interface Example 是否符合預期。
package org.ruoxue.java_147.functional.unaryoperator;
import static org.junit.Assert.*;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.UnaryOperator;
import java.util.stream.Collectors;
import java.util.stream.Stream;
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 UnaryOperatorInterfaceTest {
@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 Optional_map() {
Optional<String> opt = Optional.ofNullable("Bacon");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
Optional<String> toUpperCaseOpt = opt.map(toUpperCase);
String result = toUpperCaseOpt.orElse("");
System.out.println(result);
assertEquals("BACON", result);
Optional<Food> foodOpt = Optional.ofNullable(new Food("Ham", 1, 1));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Optional<Food> booleanOpt = foodOpt.map(addition.andThen(multiply));
Food foodResult = booleanOpt.orElse(null);
System.out.println(foodResult);
assertNotNull(foodResult);
}
@Test
public void Stream_map() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
Stream<String> stream = list.stream().map(toUpperCase);
long count = stream.peek(System.out::println).count();
assertEquals(expectedSize, count);
List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Stream<Food> foodStream = foodList.stream().map(addition.andThen(multiply));
count = foodStream.peek(System.out::println).count();
assertEquals(expectedSize, count);
}
@Test
public void Stream_flatMap() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> toUpperCase = String::toUpperCase;
List<String> result = list.stream().map(toUpperCase).collect(Collectors.toList());
System.out.println(result);
assertEquals(expectedSize, result.size());
List<List<String>> nestedlist = Arrays.asList(Arrays.asList("Bacon"), Arrays.asList("Ham"),
Arrays.asList("Pork"));
List<String> nestedResult = nestedlist.stream().flatMap(Collection::stream).collect(Collectors.toList());
System.out.println(nestedResult);
assertEquals(expectedSize, nestedResult.size());
}
@Test
public void Map_computeIfAbsent() {
Map<String, String> map = new HashMap<String, String>();
map.put("Bacon", "Bacon");
map.put("Ham", "Ham");
map.put("Pork", "Pork");
UnaryOperator<String> toUpperCase = s -> s.toUpperCase();
String result = map.computeIfAbsent("Bread", toUpperCase);
System.out.println(map);
assertEquals("BREAD", result);
Map<Food, Food> foodMap = new HashMap<Food, Food>();
foodMap.put(new Food("Bacon", 1, 1), new Food("Bacon", 1, 1));
foodMap.put(new Food("Ham", 2, 1), new Food("Ham", 1, 2));
foodMap.put(new Food("Pork", 3, 1), new Food("Pork", 1, 3));
UnaryOperator<Food> addition = o -> {
o.setQuantity(o.getQuantity() + 3);
return o;
};
UnaryOperator<Food> multiply = o -> {
o.setQuantity(o.getQuantity() * 2);
return o;
};
Food foodResult = foodMap.computeIfAbsent(new Food("Bread", 1, 1), addition.andThen(multiply));
System.out.println(foodMap);
assertEquals(8d, foodResult.getQuantity(), 2);
}
@Test
public void Collectors_toMap() {
int expectedSize = 3;
List<String> list = Arrays.asList("Bacon", "Ham", "Pork");
UnaryOperator<String> key = s -> s.toUpperCase();
UnaryOperator<String> toLowerCase = s -> s.toLowerCase();
Map<String, String> map = list.stream().collect(Collectors.toMap(key, toLowerCase));
System.out.println(map);
assertEquals(expectedSize, map.size());
List<Food> foodList = Arrays.asList(new Food("Bacon", 1, 1), new Food("Ham", 2, 1), new Food("Pork", 3, 1));
UnaryOperator<Food> foodKey = o -> o;
UnaryOperator<Food> half = o -> {
o.setQuantity(o.getQuantity() / 2);
return o;
};
UnaryOperator<Food> twice = o -> {
o.setQuantity(o.getQuantity() * o.getQuantity());
return o;
};
Map<Food, Food> foodMap = foodList.stream().collect(Collectors.toMap(foodKey, half.andThen(twice)));
System.out.println(foodMap);
assertEquals(expectedSize, foodMap.size());
}
}
心得分享
Java UnaryOperator Interface Example 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, UnaryOperator Interface in Java 提供了幾種 UnaryOperator 常見方法的操作範例,熟悉這些方法的操作,能夠提高開發效率,節省維護上的成本。