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add Optional examples · java8/Java8InAction@150e8bd · GitHub

/ Java8InAction Public

Commit 150e8bd

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mariofusco
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add Optional examples
1 parent 442ef0e commit 150e8bd

6 files changed

Lines changed: 105 additions & 2 deletions

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‎pom.xml‎

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@@ -16,8 +16,7 @@
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.8.1</version>
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<scope>test</scope>
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<version>4.11</version>
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</dependency>
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</dependencies>
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‎src/main/java/lambdasinaction/chap9/Car.java‎

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package lambdasinaction.chap9;
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import java.util.*;
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public class Car {
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private Optional<Insurance> insurance;
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public Optional<Insurance> getInsurance() {
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return insurance;
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}
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}

‎src/main/java/lambdasinaction/chap9/Insurance.java‎

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package lambdasinaction.chap9;
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public class Insurance {
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private String name;
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public String getName() {
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return name;
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}
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}

‎src/main/java/lambdasinaction/chap9/OptionalMain.java‎

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package lambdasinaction.chap9;
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import java.util.*;
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public class OptionalMain {
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public String getCarInsuranceName(Optional<Person> person) {
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return person.flatMap(Person::getCar)
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.flatMap(Car::getInsurance)
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.map(Insurance::getName)
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.orElse("Unknown");
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}
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}

‎src/main/java/lambdasinaction/chap9/Person.java‎

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package lambdasinaction.chap9;
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import java.util.*;
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public class Person {
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private Optional<Car> car;
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public Optional<Car> getCar() {
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return car;
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}
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}

‎src/main/java/lambdasinaction/chap9/ReadPositiveIntParam.java‎

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package lambdasinaction.chap9;
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import org.junit.*;
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import java.util.*;
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import static java.util.Optional.*;
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import static org.junit.Assert.assertEquals;
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public class ReadPositiveIntParam {
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@Test
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public void testMap() {
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Properties props = new Properties();
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props.setProperty("a", "5");
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props.setProperty("b", "true");
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props.setProperty("c", "-3");
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assertEquals(5, readDurationImperative(props, "a"));
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assertEquals(0, readDurationImperative(props, "b"));
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assertEquals(0, readDurationImperative(props, "c"));
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assertEquals(0, readDurationImperative(props, "d"));
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assertEquals(5, readDurationWithOptional(props, "a"));
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assertEquals(0, readDurationWithOptional(props, "b"));
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assertEquals(0, readDurationWithOptional(props, "c"));
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assertEquals(0, readDurationWithOptional(props, "d"));
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}
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public static int readDurationImperative(Properties props, String name) {
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String value = props.getProperty(name);
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if (value != null) {
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try {
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int i = Integer.parseInt(value);
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if (i > 0) {
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return i;
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}
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} catch (NumberFormatException nfe) { }
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}
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return 0;
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}
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public static int readDurationWithOptional(Properties props, String name) {
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return ofNullable(props.getProperty(name))
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.flatMap(ReadPositiveIntParam::s2i)
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.filter(i -> i > 0).orElse(0);
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}
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public static Optional<Integer> s2i(String s) {
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try {
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return of(Integer.parseInt(s));
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} catch (NumberFormatException e) {
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return empty();
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}
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}
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}

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