Merge pull request #6712 from Doha2012/master

add generic constructor examples

core-java-lang-oop-2/src/main/java/com/baeldung/generics/Entry.java

@@ -0,0 +1,38 @@
+package com.baeldung.generics;
+
+import java.io.Serializable;
+
+public class Entry {
+    private String data;
+    private int rank;
+
+    // non-generic constructor
+    public Entry(String data, int rank) {
+        this.data = data;
+        this.rank = rank;
+    }
+
+    // generic constructor
+    public <E extends Rankable & Serializable> Entry(E element) {
+        this.data = element.toString();
+        this.rank = element.getRank();
+    }
+
+    // getters and setters
+    public String getData() {
+        return data;
+    }
+
+    public void setData(String data) {
+        this.data = data;
+    }
+
+    public int getRank() {
+        return rank;
+    }
+
+    public void setRank(int rank) {
+        this.rank = rank;
+    }
+
+}

core-java-lang-oop-2/src/main/java/com/baeldung/generics/GenericEntry.java

@@ -0,0 +1,53 @@
+package com.baeldung.generics;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+public class GenericEntry<T> {
+    private T data;
+    private int rank;
+
+    // non-generic constructor
+    public GenericEntry(int rank) {
+        this.rank = rank;
+    }
+
+    // generic constructor
+    public GenericEntry(T data, int rank) {
+        this.data = data;
+        this.rank = rank;
+    }
+
+    // generic constructor with different type
+    public <E extends Rankable & Serializable> GenericEntry(E element) {
+        this.data = (T) element;
+        this.rank = element.getRank();
+    }
+
+    // generic constructor with different type and wild card
+    public GenericEntry(Optional<? extends Rankable> optional) {
+        if (optional.isPresent()) {
+            this.data = (T) optional.get();
+            this.rank = optional.get()
+                .getRank();
+        }
+    }
+
+    // getters and setters
+    public T getData() {
+        return data;
+    }
+
+    public void setData(T data) {
+        this.data = data;
+    }
+
+    public int getRank() {
+        return rank;
+    }
+
+    public void setRank(int rank) {
+        this.rank = rank;
+    }
+
+}

core-java-lang-oop-2/src/main/java/com/baeldung/generics/MapEntry.java

@@ -0,0 +1,34 @@
+package com.baeldung.generics;
+
+public class MapEntry<K, V> {
+    private K key;
+    private V value;
+
+    public MapEntry() {
+        super();
+    }
+
+    // generic constructor with two parameters
+    public MapEntry(K key, V value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    // getters and setters
+    public K getKey() {
+        return key;
+    }
+
+    public void setKey(K key) {
+        this.key = key;
+    }
+
+    public V getValue() {
+        return value;
+    }
+
+    public void setValue(V value) {
+        this.value = value;
+    }
+
+}

core-java-lang-oop-2/src/main/java/com/baeldung/generics/Product.java

@@ -0,0 +1,50 @@
+package com.baeldung.generics;
+
+import java.io.Serializable;
+
+public class Product implements Rankable, Serializable {
+    private String name;
+    private double price;
+    private int sales;
+
+    public Product(String name, double price) {
+        this.name = name;
+        this.price = price;
+    }
+
+    @Override
+    public int getRank() {
+        return sales;
+    }
+
+    @Override
+    public String toString() {
+        return "Product [name=" + name + ", price=" + price + ", sales=" + sales + "]";
+    }
+
+    // getters and setters
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public double getPrice() {
+        return price;
+    }
+
+    public void setPrice(double price) {
+        this.price = price;
+    }
+
+    public int getSales() {
+        return sales;
+    }
+
+    public void setSales(int sales) {
+        this.sales = sales;
+    }
+
+}

core-java-lang-oop-2/src/main/java/com/baeldung/generics/Rankable.java

@@ -0,0 +1,5 @@
+package com.baeldung.generics;
+
+public interface Rankable {
+    public int getRank();
+}

core-java-lang-oop-2/src/test/java/com/baeldung/generics/GenericConstructorUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.generics;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+import org.junit.Test;
+
+public class GenericConstructorUnitTest {
+
+    @Test
+    public void givenNonGenericConstructor_whenCreateNonGenericEntry_thenOK() {
+        Entry entry = new Entry("sample", 1);
+
+        assertEquals("sample", entry.getData());
+        assertEquals(1, entry.getRank());
+    }
+
+    @Test
+    public void givenGenericConstructor_whenCreateNonGenericEntry_thenOK() {
+        Product product = new Product("milk", 2.5);
+        product.setSales(30);
+        Entry entry = new Entry(product);
+
+        assertEquals(product.toString(), entry.getData());
+        assertEquals(30, entry.getRank());
+    }
+
+    @Test
+    public void givenNonGenericConstructor_whenCreateGenericEntry_thenOK() {
+        GenericEntry<String> entry = new GenericEntry<String>(1);
+
+        assertNull(entry.getData());
+        assertEquals(1, entry.getRank());
+    }
+
+    @Test
+    public void givenGenericConstructor_whenCreateGenericEntry_thenOK() {
+        GenericEntry<String> entry = new GenericEntry<String>("sample", 1);
+
+        assertEquals("sample", entry.getData());
+        assertEquals(1, entry.getRank());
+    }
+
+    @Test
+    public void givenGenericConstructorWithDifferentType_whenCreateGenericEntry_thenOK() {
+        Product product = new Product("milk", 2.5);
+        product.setSales(30);
+        GenericEntry<Serializable> entry = new GenericEntry<Serializable>(product);
+
+        assertEquals(product, entry.getData());
+        assertEquals(30, entry.getRank());
+    }
+
+    @Test
+    public void givenGenericConstructorWithWildCard_whenCreateGenericEntry_thenOK() {
+        Product product = new Product("milk", 2.5);
+        product.setSales(30);
+        Optional<Product> optional = Optional.of(product);
+        GenericEntry<Serializable> entry = new GenericEntry<Serializable>(optional);
+
+        assertEquals(product, entry.getData());
+        assertEquals(30, entry.getRank());
+    }
+
+    @Test
+    public void givenGenericConstructor_whenCreateGenericEntryWithTwoTypes_thenOK() {
+        MapEntry<String, Integer> entry = new MapEntry<String, Integer>("sample", 1);
+
+        assertEquals("sample", entry.getKey());
+        assertEquals(1, entry.getValue()
+            .intValue());
+    }
+}