[JAVA-621] core-java-lang-oop-generics module
* Creation * Moved code from https://www.baeldung.com/raw-types-java * Moved code from https://www.baeldung.com/java-generic-constructors * Moved code from https://www.baeldung.com/java-type-erasure * Moved article references to the new README.md
This commit is contained in:
dupirefr
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This module contains articles about Object-oriented programming (OOP) in Java
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### Relevant Articles:
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- [Generic Constructors in Java](https://www.baeldung.com/java-generic-constructors)
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- [Anonymous Classes in Java](https://www.baeldung.com/java-anonymous-classes)
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- [Raw Types in Java](https://www.baeldung.com/raw-types-java)
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- [Marker Interfaces in Java](https://www.baeldung.com/java-marker-interfaces)
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- [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
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- [Static and Default Methods in Interfaces in Java](https://www.baeldung.com/java-static-default-methods)
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package com.baeldung.generics;
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import java.io.Serializable;
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public class Entry {
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private String data;
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private int rank;
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// non-generic constructor
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public Entry(String data, int rank) {
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this.data = data;
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this.rank = rank;
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}
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// generic constructor
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public <E extends Rankable & Serializable> Entry(E element) {
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this.data = element.toString();
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this.rank = element.getRank();
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}
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// getters and setters
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public String getData() {
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return data;
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}
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public void setData(String data) {
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this.data = data;
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}
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public int getRank() {
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return rank;
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}
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public void setRank(int rank) {
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this.rank = rank;
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}
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}
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@@ -1,53 +0,0 @@
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package com.baeldung.generics;
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import java.io.Serializable;
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import java.util.Optional;
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public class GenericEntry<T> {
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private T data;
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private int rank;
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// non-generic constructor
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public GenericEntry(int rank) {
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this.rank = rank;
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}
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// generic constructor
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public GenericEntry(T data, int rank) {
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this.data = data;
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this.rank = rank;
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}
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// generic constructor with different type
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public <E extends Rankable & Serializable> GenericEntry(E element) {
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this.data = (T) element;
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this.rank = element.getRank();
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}
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// generic constructor with different type and wild card
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public GenericEntry(Optional<? extends Rankable> optional) {
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if (optional.isPresent()) {
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this.data = (T) optional.get();
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this.rank = optional.get()
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.getRank();
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}
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}
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// getters and setters
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public T getData() {
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return data;
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}
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public void setData(T data) {
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this.data = data;
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}
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public int getRank() {
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return rank;
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}
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public void setRank(int rank) {
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this.rank = rank;
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}
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}
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package com.baeldung.generics;
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public class MapEntry<K, V> {
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private K key;
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private V value;
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public MapEntry() {
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super();
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}
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// generic constructor with two parameters
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public MapEntry(K key, V value) {
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this.key = key;
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this.value = value;
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}
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// getters and setters
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public K getKey() {
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return key;
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}
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public void setKey(K key) {
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this.key = key;
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}
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public V getValue() {
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return value;
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}
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public void setValue(V value) {
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this.value = value;
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}
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}
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@@ -1,50 +0,0 @@
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package com.baeldung.generics;
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import java.io.Serializable;
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public class Product implements Rankable, Serializable {
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private String name;
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private double price;
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private int sales;
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public Product(String name, double price) {
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this.name = name;
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this.price = price;
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}
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@Override
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public int getRank() {
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return sales;
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}
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@Override
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public String toString() {
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return "Product [name=" + name + ", price=" + price + ", sales=" + sales + "]";
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}
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// getters and setters
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public double getPrice() {
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return price;
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}
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public void setPrice(double price) {
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this.price = price;
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}
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public int getSales() {
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return sales;
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}
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public void setSales(int sales) {
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this.sales = sales;
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}
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}
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@@ -1,5 +0,0 @@
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package com.baeldung.generics;
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public interface Rankable {
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public int getRank();
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}
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@@ -1,25 +0,0 @@
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package com.baeldung.rawtype;
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import java.util.ArrayList;
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import java.util.List;
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public class RawTypeDemo {
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public static void main(String[] args) {
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RawTypeDemo rawTypeDemo = new RawTypeDemo();
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rawTypeDemo.methodA();
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}
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public void methodA() {
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// parameterized type
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List<String> listStr = new ArrayList<>();
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listStr.add("Hello Folks!");
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methodB(listStr);
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String s = listStr.get(1); // ClassCastException at run time
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}
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public void methodB(List rawList) { // Inexpressive raw type
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rawList.add(1); // Unsafe operation
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}
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}
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@@ -1,76 +0,0 @@
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package com.baeldung.generics;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertNull;
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import java.io.Serializable;
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import java.util.Optional;
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import org.junit.Test;
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public class GenericConstructorUnitTest {
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@Test
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public void givenNonGenericConstructor_whenCreateNonGenericEntry_thenOK() {
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Entry entry = new Entry("sample", 1);
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assertEquals("sample", entry.getData());
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assertEquals(1, entry.getRank());
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}
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@Test
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public void givenGenericConstructor_whenCreateNonGenericEntry_thenOK() {
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Product product = new Product("milk", 2.5);
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product.setSales(30);
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Entry entry = new Entry(product);
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assertEquals(product.toString(), entry.getData());
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assertEquals(30, entry.getRank());
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}
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@Test
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public void givenNonGenericConstructor_whenCreateGenericEntry_thenOK() {
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GenericEntry<String> entry = new GenericEntry<String>(1);
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assertNull(entry.getData());
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assertEquals(1, entry.getRank());
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}
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@Test
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public void givenGenericConstructor_whenCreateGenericEntry_thenOK() {
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GenericEntry<String> entry = new GenericEntry<String>("sample", 1);
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assertEquals("sample", entry.getData());
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assertEquals(1, entry.getRank());
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}
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@Test
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public void givenGenericConstructorWithDifferentType_whenCreateGenericEntry_thenOK() {
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Product product = new Product("milk", 2.5);
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product.setSales(30);
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GenericEntry<Serializable> entry = new GenericEntry<Serializable>(product);
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assertEquals(product, entry.getData());
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assertEquals(30, entry.getRank());
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}
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@Test
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public void givenGenericConstructorWithWildCard_whenCreateGenericEntry_thenOK() {
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Product product = new Product("milk", 2.5);
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product.setSales(30);
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Optional<Product> optional = Optional.of(product);
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GenericEntry<Serializable> entry = new GenericEntry<Serializable>(optional);
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assertEquals(product, entry.getData());
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assertEquals(30, entry.getRank());
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}
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@Test
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public void givenGenericConstructor_whenCreateGenericEntryWithTwoTypes_thenOK() {
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MapEntry<String, Integer> entry = new MapEntry<String, Integer>("sample", 1);
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assertEquals("sample", entry.getKey());
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assertEquals(1, entry.getValue()
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.intValue());
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}
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}
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