BAEL-3091: The Prototype Pattern in Java (changed code based on valid comments from a reader)

immutables/src/main/java/com/baeldung/immutable/Address.java

@@ -0,0 +1,9 @@
+package com.baeldung.immutable;
+
+import org.immutables.value.Value;
+
+@Value.Immutable
+public interface Address {
+    String getStreetName();
+    Integer getNumber();
+}

immutables/src/main/java/com/baeldung/immutable/Person.java

@@ -0,0 +1,9 @@
+package com.baeldung.immutable;
+
+import org.immutables.value.Value;
+
+@Value.Immutable
+public abstract class Person {
+    abstract String getName();
+    abstract Integer getAge();
+}

immutables/src/main/java/com/baeldung/immutable/auxiliary/Person.java

@@ -0,0 +1,13 @@
+package com.baeldung.immutable.auxiliary;
+
+
+import org.immutables.value.Value;
+
+@Value.Immutable
+public abstract class Person {
+    abstract String getName();
+    abstract Integer getAge();
+
+    @Value.Auxiliary
+    abstract String getAuxiliaryField();
+}

immutables/src/main/java/com/baeldung/immutable/default_/Person.java

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+package com.baeldung.immutable.default_;
+
+import org.immutables.value.Value;
+
+@Value.Immutable(prehash = true)
+public abstract class Person {
+
+    abstract String getName();
+
+    @Value.Default
+    Integer getAge() {
+        return 42;
+    }
+}

immutables/src/main/java/com/baeldung/immutable/parameter/Person.java

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+package com.baeldung.immutable.parameter;
+
+
+import org.immutables.value.Value;
+
+@Value.Immutable
+public abstract class Person {
+
+    @Value.Parameter
+    abstract String getName();
+
+    @Value.Parameter
+    abstract Integer getAge();
+}

immutables/src/main/java/com/baeldung/immutable/prehash/Person.java

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+package com.baeldung.immutable.prehash;
+
+import org.immutables.value.Value;
+
+@Value.Immutable(prehash = true)
+public abstract class Person {
+    abstract String getName();
+    abstract Integer getAge();
+}

immutables/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

immutables/src/test/java/com/baeldung/immutable/ImmutablePersonUnitTest.java

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+package com.baeldung.immutable;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mutabilitydetector.unittesting.MutabilityAssert.assertImmutable;
+
+public class ImmutablePersonUnitTest {
+
+    @Test
+    public void whenModifying_shouldCreateNewInstance() throws Exception {
+        final ImmutablePerson john = ImmutablePerson.builder()
+          .age(42)
+          .name("John")
+          .build();
+
+        final ImmutablePerson john43 = john.withAge(43);
+
+        assertThat(john)
+          .isNotSameAs(john43);
+
+        assertThat(john.getAge())
+          .isEqualTo(42);
+
+        assertImmutable(ImmutablePerson.class);
+    }
+}

immutables/src/test/java/com/baeldung/immutable/auxiliary/ImmutablePersonAuxiliaryUnitTest.java

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+package com.baeldung.immutable.auxiliary;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ImmutablePersonAuxiliaryUnitTest {
+
+    @Test
+    public void whenComparing_shouldIgnore() throws Exception {
+        final ImmutablePerson john1 = ImmutablePerson.builder()
+          .name("John")
+          .age(42)
+          .auxiliaryField("Value1")
+          .build();
+
+        final ImmutablePerson john2 = ImmutablePerson.builder()
+          .name("John")
+          .age(42)
+          .auxiliaryField("Value2")
+          .build();
+
+
+        assertThat(john1.equals(john2))
+          .isTrue();
+
+        assertThat(john1.toString())
+          .isEqualTo(john2.toString());
+
+        assertThat(john1.hashCode())
+          .isEqualTo(john2.hashCode());
+    }
+}

immutables/src/test/java/com/baeldung/immutable/default_/ImmutablePersonDefaultUnitTest.java

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+package com.baeldung.immutable.default_;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ImmutablePersonDefaultUnitTest {
+
+    @Test
+    public void whenInstantiating_shouldUseDefaultValue() throws Exception {
+
+        final ImmutablePerson john = ImmutablePerson.builder().name("John").build();
+
+        assertThat(john.getAge()).isEqualTo(42);
+
+    }
+}