Table of Contents
ToggleJava UnaryOperator Methods
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,常用於物件轉換或數字運算,傳入 1 個泛型物件參數,結果傳回同型別物件,可以使用 andThen 、 compose 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,UnaryOperator Java Methods 介紹常見的 apply 、 andThen 、 compose 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
| +- UnaryOperatorMethodsTest.java
單元測試
UnaryOperator Java Methods 提供 apply 、 andThen 、 compose 條件或組合成鏈式判斷等操作 UnaryOperator 。
apply
建立 UnaryOperator 物件,傳入 1 個參數,執行程式邏輯,傳回物件。
@Test
public void apply() {
UnaryOperator<String> upperCase = s -> s.toUpperCase();
String result = upperCase.apply("Bacon");
System.out.println(result);
assertEquals("BACON", result);
result = upperCase.apply("Ham");
System.out.println(result);
assertEquals("HAM", result);
UnaryOperator<Integer> addition = i -> i + 3;
Integer intResult = addition.apply(5);
System.out.println(result);
assertEquals(new Integer(8), intResult);
}
true
false
true
false
andThen
UnaryOperator Java Methods 建立 2 個 UnaryOperator 物件,傳入 1 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() {
UnaryOperator<Double> half = d -> d / 2;
UnaryOperator<Double> twice = d -> d * d;
double result = half.andThen(twice).apply(5d);
System.out.println(result);
assertEquals(6.25d, result, 2);
UnaryOperator<String> lowerCase = s -> s.toLowerCase();
UnaryOperator<String> concat = s -> s.concat("B");
String stringResult = lowerCase.andThen(concat).apply("Bacon");
System.out.println(stringResult);
assertEquals("baconB", stringResult);
}
6.25
baconB
andThenThrowException
UnaryOperator Java Methods 建立 UnaryOperator 物件,傳入參數 null ,會拋出例外 。
@SuppressWarnings({ "unchecked", "rawtypes" })
@Test(expected = NullPointerException.class)
public void andThenThrowException() {
UnaryOperator<Double> half = d -> d / 2;
half = (UnaryOperator) half.andThen(null);
}
java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.function.Function.andThen(Function.java:87)
at org.ruoxue.java_147.functional.unaryoperator.UnaryOperatorMethodsTest.andThenThrowException(UnaryOperatorMethodsTest.java:46)
compose
UnaryOperator Java Methods 建立 2 個 UnaryOperator 物件,傳入 1 個參數,使用 compose 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 compose() {
UnaryOperator<Double> half = d -> d / 2;
UnaryOperator<Double> twice = d -> d * d;
double result = half.compose(twice).apply(5d);
System.out.println(result);
assertEquals(12.5, result, 2);
}
12.5
composeThrowException
UnaryOperator Methods in Java 建立 UnaryOperator 物件,傳入參數 null ,會拋出例外 。
@Test(expected = NullPointerException.class)
public void composeThrowException() {
Function<Double, Double> half = d -> d / 2;
half = half.compose(null);
}
java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.function.Function.compose(Function.java:67)
at org.ruoxue.java_147.functional.unaryoperator.UnaryOperatorMethodsTest.composeThrowException(UnaryOperatorMethodsTest.java:62)
identity
UnaryOperator Methods in Java 建立 UnaryOperator 物件,傳入 1 個參數,傳回參數。
@Test
public void identity() {
UnaryOperator<String> identity = UnaryOperator.identity();
String result = identity.apply("Bacon");
System.out.println(result);
assertEquals("Bacon", result);
Object objResult = UnaryOperator.identity().apply("Ham");
System.out.println(objResult);
assertEquals("Ham", objResult);
UnaryOperator<Integer> intIdentity = i -> i;
int intResult = intIdentity.apply(7);
System.out.println(intResult);
assertEquals(7, intResult);
}
Bacon
Ham
7
traditional
UnaryOperator Methods in Java 使用傳統方式,實作 UnaryOperator 接口,傳回物件。
public static class ToUpperCase<E> implements UnaryOperator<String> {
@Override
public String apply(String t) {
return t.toUpperCase();
}
}
@Test
public void traditional() {
UnaryOperator<String> toUpperCase = new ToUpperCase<String>();
UnaryOperator<String> toLowerCase = s -> s.toLowerCase();
String result = toUpperCase.andThen(toLowerCase).apply("Bacon");
System.out.println(result);
assertEquals("bacon", result);
result = toUpperCase.andThen(toLowerCase).apply("Ham");
System.out.println(result);
assertEquals("ham", result);
}
bacon
ham
UnaryOperatorMethodsTest.java
UnaryOperator Methods in Java 新增單元測試,驗證 UnaryOperator Functions in Java 是否符合預期。
package org.ruoxue.java_147.functional.unaryoperator;
import static org.junit.Assert.*;
import java.util.function.UnaryOperator;
import org.junit.Test;
public class UnaryOperatorMethodsTest {
@Test
public void apply() {
UnaryOperator<String> upperCase = s -> s.toUpperCase();
String result = upperCase.apply("Bacon");
System.out.println(result);
assertEquals("BACON", result);
result = upperCase.apply("Ham");
System.out.println(result);
assertEquals("HAM", result);
UnaryOperator<Integer> addition = i -> i + 3;
Integer intResult = addition.apply(5);
System.out.println(intResult);
assertEquals(new Integer(8), intResult);
}
@Test
public void andThen() {
UnaryOperator<Double> half = d -> d / 2;
UnaryOperator<Double> twice = d -> d * d;
double result = half.andThen(twice).apply(5d);
System.out.println(result);
assertEquals(6.25d, result, 2);
UnaryOperator<String> lowerCase = s -> s.toLowerCase();
UnaryOperator<String> concat = s -> s.concat("B");
String stringResult = lowerCase.andThen(concat).apply("Bacon");
System.out.println(stringResult);
assertEquals("baconB", stringResult);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
@Test(expected = NullPointerException.class)
public void andThenThrowException() {
UnaryOperator<Double> half = d -> d / 2;
half = (UnaryOperator) half.andThen(null);
}
@Test
public void compose() {
UnaryOperator<Double> half = d -> d / 2;
UnaryOperator<Double> twice = d -> d * d;
double result = half.compose(twice).apply(5d);
System.out.println(result);
assertEquals(12.5, result, 2);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
@Test(expected = NullPointerException.class)
public void composeThrowException() {
UnaryOperator<Double> half = d -> d / 2;
half = (UnaryOperator) half.compose(null);
}
@Test
public void identity() {
UnaryOperator<String> identity = UnaryOperator.identity();
String result = identity.apply("Bacon");
System.out.println(result);
assertEquals("Bacon", result);
Object objResult = UnaryOperator.identity().apply("Ham");
System.out.println(objResult);
assertEquals("Ham", objResult);
UnaryOperator<Integer> intIdentity = i -> i;
int intResult = intIdentity.apply(7);
System.out.println(intResult);
assertEquals(7, intResult);
}
public static class ToUpperCase<E> implements UnaryOperator<String> {
@Override
public String apply(String t) {
return t.toUpperCase();
}
}
@Test
public void traditional() {
UnaryOperator<String> toUpperCase = new ToUpperCase<String>();
UnaryOperator<String> toLowerCase = s -> s.toLowerCase();
String result = toUpperCase.andThen(toLowerCase).apply("Bacon");
System.out.println(result);
assertEquals("bacon", result);
result = toUpperCase.andThen(toLowerCase).apply("Ham");
System.out.println(result);
assertEquals("ham", result);
}
}
心得分享
UnaryOperator Functions in Java 屬於 java.util.function ,常用於物件轉換或數字運算,例如:取得字串長度、數字加減乘除運算, 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 Methods in Java 提供更清晰、更易讀且更靈活的方式來組合多個 UnaryOperator 條件,來表示非常複雜的邏輯條件,如: apply 、 andThen 、 compose 等,提供了幾種 UnaryOperator 常見範例。